- Mpi-22 - mailman3.cels.anl.gov

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 09 Dec '08

09 Dec '08

Ok, now that I've gotten my user's point of view off my chest, back to my view as an MPI implementer. I've tried to respond to all Alexander's objections. If I missed one, I apologize. > 1) The memory remapping scenario IO brought up a couple of days ago Unless someone's done something fun with operating system and architecture design I'm not aware of, remapping has one problem that always must be considered... Send buffers are not required to be (and frequently aren't) page aligned or a multiple of page size. Therefore, completely removing the send buffer from the user's process has the problem of also taking legal addresses with it (which would violate the standard). IBM's solution is elegant in that it allows remapping without removing from the sender's process space. Sandia has a solution called SMARTMAP that is both not patented and allows single copy transfers in shared memory environments. Point number 2 was a procedural argument. I believe others are in a better position than I to comment on this. My understanding, however, is that a technical objection can cause the vote to fail, but is not grounds on preventing a vote (particularly a second vote). If it were, we'd never get anything done. > 3) Imagine send buffers have to pinned in the memory. To avoid doing this too > often, these registrations will normally be cached. If more than one send can > be used for a buffer or, for that matter, overlapping portions of the same > buffer, say by different threads, access to the lookup-and-pin will have to be > made atomic. This will further complicate implementation and introduce a > potentially costly mutual exclusion primitive into the critical path. The caching problem already exists. Consider a case where a large send is completed, then multiple small sends occur within that base and bound after the first is completed. This situation is perfectly legal, happens in codes in the wild, and must be dealt with by MPI implementations. If that's not enough, consider a case where the buffer is part of an active Window (which is legal, as long as the buffers in use for communication don't overlap). All these cases certainly should be handled by an MPI today. > 4) I wonder what a const modifier will do for a buffer identifies by > MPI_BOTTOM and/or a derived data type, possibly with holes in it. How will > this square up with the C language sequence association rules? This sounds like an issue for the const proposal, which is different from the send buffer access proposal. I'm not sure I have enough data to form an opinion on the const proposal, but I'm fairly sure we can discuss the send buffer access proposal without considering this issue. > 5) Note also if both #45 and #46 will be introduced, there will be no way to > retract this, even with the help of the MPI_INIT_ASSERTED, should we later > decide to introduce assertion like MPI_NO_SEND_BUFFER_READ_ACCESS. The const > modifier from #46 will make that syntactically useless. If both are passed, that might be true. It could be argued the const proposal depends on the access proposal. However, it can not be rationally argued that the access proposal in any way depends upon the const proposal. The send buffer access proposal can certainly be passed and an assert added later (at whatever point the init_assert proposal is integrated into the standard) that allows MPI implementations to modify the send buffer. You raise a good point about the const proposal. But it has absolutely no bearing on the send buffer access proposal. > 6) Finally, what will happen in the Fortran interface? With the > copy-in/copy-out possibly happening on the MPI subroutine boundary for array > sections? If more than one send is allowed, the application can pretty easily > exhaust any virtual memory with a couple of long enough vectors. How does that change from today? Today users send multiple buffers at the same time, and seem to cope with memory exhaustion issues just fine. So soon they might be able to remove the data copy they've had to make at the user level to work around the MPI access restriction, so there's actually less virtual memory in use. Seems like a win to me. > 7) In-place compression and/or encryption of the messages. Compression in > particular can work wonders on monotonous messages, and cost less time in > total than the transmission of so many giga-zeroes, for example. Again, having > send buffer access allowed and const modifier attached will kill this huge > optimization opportunity. Too bad. While I hope you're joking about the giga-zeros, you do raise a valid concern, in that there are a number of optimizations regarding compression, encryption, and endian-swapping that may be eliminated by this proposal. On the flip side, as I argued in a previous e-mail, the user gains quite a bit in usability. We have to balance these two factors. Since users know where my office is, I tend to lean towards making their lives easier, particularly when it doesn't cause extra work for me. But I already sent an e-mail on that point... Our experience with Open MPI was that the potential for performance in other parts of the MPI (collectives, etc.) far outweighed any send-side tricks we could think of (and you haven't brought up any we didn't think of). So if we wanted to do compression or encryption, it would be done with send-side bounce buffers. Since a software pipeline would practically be required to get good performance, the bounce buffer would not have to scale with the size of the communication buffer but instead with the properties of the network pipeline. Of course, my opinion would be that it would be much simpler and much higher performance to support compression or encryption as part of the NIC as the data is streamed to the network. Otherwise, you're burning memory bandwidth doing the extra copy (even in the modify the send buffer case), and memory bandwidth is a precious resource for HPC applications. One other point to consider. If I was a user, I'd expect that my one-sided traffic also be compressed, encrypted, or endian-swapped. The standard already requires multiple accesses be legal for one-sided communication. So you're going to have a situation where some communication can use a send-modify implementation and some can not. I'm not familiar with how Intel's MPI is architected, but Open MPI is architected such that decisions such as compression, encryption, and endian-swapping would be made at a low enough level that the code path is the same whether the message is a point-to-point send or a one-sided put. Since that's some of the most complicated code in Open MPI, I can't foresee adding a second code path just to get a (dubious) performance benefit. Brian -- Brian W. Barrett Dept. 1422: Scalable Computer Architectures Sandia National Laboratories

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 09 Dec '08

09 Dec '08

For reasons I'm not sure I completely understand, the discussion on this proposal has become focused on micro-optimizations for MPI implementations, rather than the original desire to fix one of the many usability complaints users have with the MPI standard. I personally believe that the send buffer restriction places an onerous burden on the developer of modern MPI applications. While it's straight-forward to ensure a buffer is not used multiple times for simple ghost cell transfers in basic physics codes, it can be more challenging in more advanced applications. We already know of one application in the wild that reuses send buffers (the Parallel BGL). I'm certain that if we polled application writers, we'd find even more which violate the restriction. Even as an MPI implementer who knows what he's doing (in theory, anyway), I find this restriction can be a difficult problem to work around. Further, this is a difficult issue to detect. Yes, a correctness-checking library can track buffers in use. But consider that buffer reuse is likely to be quite transient, and correctness-checking libraries frequently have an extraordinary performance penalty. Normal development cycle testing likely won't cause the issue to appear, since no current mainstream MPI implementation enforces the rule and I'm doubtful that situation will change. Finally, from a user's perspective, it must look rather capricious of the standards committee that a send buffer can't be reused but a one-sided buffer can. I certainly couldn't justify to a user why the standard has such a contradiction. Do we as a committee have the right to be capricious on this issue? Certainly. Should we then wonder why there are so many people running around preaching the evils of MPI? Certainly not. So in my opinion the question really should be framed not as "Is there any optimization that such a change prohibits?", but "Does the usability of the standard outweigh the loss of *potential* optimizations?". I have to think that eliminating a common source of confusion for users is worth losing the ability to increase the performance of sending so many giga-zeros of data. Brian -- Brian W. Barrett Dept. 1422: Scalable Computer Architectures Sandia National Laboratories

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 09 Dec '08

09 Dec '08

Richard Treumann wrote: > > On a single OS under AIX, IBM MPI does map the portion of send side > memory that holds the send buffer into the receivers address space. We > do this for both contiguous and non-contiguous buffers. The mapping > lasts just long enough for the receive side CPU to do a memory copy > from send buffer to receive buffer. (see patent *7,392,256*) > > This optimization does not have any effect on the addressability of > the send buffer by the sending task. In our case, at least, this > optimization does not argue against the proposal. > This reference to the patent would be a clear indication for other implementers (such as me) to implement it using Alexander's approach (in order to avoid any problem with IBM's patent lawyers). And the change of the actual standard might limit implementers to implement Alexander's approach and might decrease the performance of their MPI implementation. (OK; 2 might's, not really a strong argument since it is not already implemented in this way; but the mapping approach seems to be quite reasonable). Or does IBM have also a patent for Alexander's approach ? Or does Intel have already a patent on this approach ? ;-) Hubert Hubert Ritzdorf NEC Europe *

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 09 Dec '08

09 Dec '08

HI everybody, Another possible complication: 7) In-place compression and/or encryption of the messages. Compression in particular can work wonders on monotonous messages, and cost less time in total than the transmission of so many giga-zeroes, for example. Again, having send buffer access allowed and const modifier attached will kill this huge optimization opportunity. Too bad. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Monday, December 08, 2008 11:58 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Dick, Thank you. Keeping the send buffer mapped upon the sender address space is surely legal. I wonder what will be happening to the sender that has, say, thousands of the outstanding MPI_Isends, all of which mapped their contents to the receiver memory. This will consume kernel memory space and possibly hardware resources. Will this be good for scalability? On a microkernel with so little memory to play with? I'd rather map the send buffer out. As for the send or receive side byte swapping, or, for that matter, any kind of reversible transformation - the receiver will certainly do this once. Note however that proposal #46 talks about collectives as well. If there are several receivers in a Bcast type operation, they will all be doing the transformation instead of the sender doing this once there and back again. The total expense will be higher for the receiver side transformation if more than two receivers are involved. Another couple of scenarios to consider: 3) Imagine send buffers have to pinned in the memory. To avoid doing this too often, these registrations will normally be cached. If more than one send can be used for a buffer or, for that matter, overlapping portions of the same buffer, say by different threads, access to the lookup-and-pin will have to be made atomic. This will further complicate implementation and introduce a potentially costly mutual exclusion primitive into the critical path. 4) I wonder what a const modifier will do for a buffer identifies by MPI_BOTTOM and/or a derived data type, possibly with holes in it. How will this square up with the C language sequence association rules? 5) Note also if both #45 and #46 will be introduced, there will be no way to retract this, even with the help of the MPI_INIT_ASSERTED, should we later decide to introduce assertion like MPI_NO_SEND_BUFFER_READ_ACCESS. The const modifier from #46 will make that syntactically useless. 6) Finally, what will happen in the Fortran interface? With the copy-in/copy-out possibly happening on the MPI subroutine boundary for array sections? If more than one send is allowed, the application can pretty easily exhaust any virtual memory with a couple of long enough vectors. I'm looking forward to your and everybody's opinion on those scenarios. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Monday, December 08, 2008 10:56 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) On a single OS under AIX, IBM MPI does map the portion of send side memory that holds the send buffer into the receivers address space. We do this for both contiguous and non-contiguous buffers. The mapping lasts just long enough for the receive side CPU to do a memory copy from send buffer to receive buffer. (see patent 7,392,256) This optimization does not have any effect on the addressability of the send buffer by the sending task. In our case, at least, this optimization does not argue against the proposal. Also, Robert and I had a chat about the byte swap trick and it seems it should be both semantically cleaner and require fewer CPU cycles to do it in the receive buffer. In the receive buffer there is no question that the application must wait for the communication to complete and the swap only needs to be done once (the message flows in with bytes in sender order and the MPI_Recv does one pass of byte swaps if required. In the send buffer trick, the swaps to receiver order must be done and then a second pass is needed to undo it) Dick Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 12/08/2008 04:11:45 PM: > [image removed] > > Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Erez Haba > > to: > > MPI 2.2 > > 12/08/2008 04:13 PM > > Sent by: > > mpi-22-bounces_at_[hidden] > > Please respond to "MPI 2.2" > > Dear Alexander, > > As far as I recall memory remapping from the main processor to a > network device was discussed before (If I recall correctly, in the > April meeting). I think that it's close enough to your scenario of > remapping to a different process for the purpose of this discussion. > > Is your case real? Do you know of systems that do that with MPI? Or > is it a hypothetical case? > > > For the review process, we do need people to review the text; we > added this requirement in the last meeting. Regardless, it does not > prevent any other person from giving feedback on the proposal. I'm > sure that Jeff or Bill can give you're a more formal definition of > the review process. > > The wiki page state that: > https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow > To advance to the first reading, a proposal must be reviewed by the > lead chapter author and three other reviewers. That review should > check the change against the standard text to ensure that the change > in context is correct; in addition, the change should be evaluated > for completeness. For changes that involve multiple chapters (but > are logically related and hence belong in a single ticket), the > respective chapter authors must review the changes in their > chapters. These reviews must be entered as comments on the ticket. > MPI 2.2 Chapter Authors > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Saturday, December 06, 2008 11:44 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I agree to respectfully disagree on this with you, for > the following two reasons: > > 1) The memory remapping scenario IO brought up a couple of days ago > was not discussed before the first voting as far as I can recall. If > you have proof to the contrary, I would most kindly ask you to > present it. If this cannot be done, I would say that a new issue has > been added to the discussion, and we may need to review its substance. > > 2) Next, I would like to see the definition of the ticket review > process that states the reviewers are supposed to only check the > proposed text for correspondence with the existing standard. My > opinion is that reviewers are there to bring both textual and > substantial concerns up when they see the need for this. So far I've > been acting on this conviction. > > I'm looking forward to the further discussion on the floor. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 7:45 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Thanks Alexander, > > I respectfully decline your proposal to suspend the review of these tickets. > I don't see any specific reference wrt text in your comments; and > you don't bring any new issue that has not been discussed before the 1st > voting. Thus I don't see any reason to suspend their review. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 4:19 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I reviewed the text and found that further polishing of > its textual aspects should be suspended until the substance is > clarified. I put a comment to this effect into the ticket, as well > as into the dependent ticket #46. In my opinion, both tickets are > not yet ready to go into the standard and should go into another > round of contemplation of their possible repercussions. > > In both cases presumed application friendliness is traded for less > freedom of implementation. Application developers who disregard the > standard now will most likely continue to do this in the future, > possibly in some other way. Restricting the freedom of > implementation to make their life easier does not seem to be an > attractive proposition to me. > > If any of the issues identified so far, or comparable issues we > cannot fathom at the moment, surface up in one of the future HPC > platforms and hinder MPI adoption or transition to MPI-2.2 there, we > will have done disservice both to the MPI standard and to the > community. I hope this will bear on the minds of those who're going > to vote on these two items at the meeting. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 12:28 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Dear Alexander, > > It is okay and encouraged for people to comment and argue on the > proposals. You can add your comments to the ticket arguing your > important points. The forum then consider that various points and > vote on the proposal. > > However for the voting process we need people to review the text and > confirm that it does not conflict with the standard and it is > reasonable (from language pov) to be included in the standard. > > If we are willing to review the text and state that it valid for the > standard, that would be great. If you have any comments on the text > please send them to me. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:26 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I'm afraid I would need to have it explained in more > detail why review may not include arguments on the substance. If > something in the proposal makes one think that the proposed matter > may be detrimental to the MPI standard and its implementations, I > consider it one's duty to point this out. > > Following up on your reply: the segfault situation you described > will make an MPI compliant program break. Thus, the implementation > will have to keep the send buffer mapped into the sending process > address space. This is a limitation on the MPI implementation that > should be taken into account during the voting. > > Another possibility that has been pointed out earlier was that the > proposed change disallows byte swap and other send buffer > conversions to be done in place. At least one historical MPI > implementation was doing this to a great avail. Who knows what is > going to happen in the future? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 11:18 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > I think that the idea is for the reviewers to check the text for any > mistakes and compatibility with the existing text, rather than check > for the validity of the proposal. The later as I recall is left for > the MPI forum assembly. > > As for your question, I'm sure that you can answer it yourself. J If > the memory is still also mapped to the original process (as with > shared memory) that everything is fine. If the memory is removed > from the original process, than the app will get an access-violation fault. > (if this system works on a page boundary, to take this action it > needs to make sure that there are no other allocation on the same page) > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:05 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Hi, > > I'd like to review this proposal. Let's consider the following scenario: > > - In the MPI_Isend, MPI maps the send buffer into the address space > of the receiving process. > - In the matching MPI_Recv, the receiving process makes a copy of > the mapped send buffer into the receive buffer. > - Once the copy is complete, the send buffer is mapped back into the > sender address space during the wait/test call. > > What will happen one tries to access the send buffer in between? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 10:48 PM > To: MPI 2.2 > Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) > This proposal has passed 1st voting and needs reviewers. We need 3 volunteers > to sign-off on this proposal, plus the 3 chapter authors to sign-off > on the text. > > The Chapter Authors for > > Chapter 3: Point-to-Point Communication > Chapter 5: Collective Communication > Chapter 11: One-Sided Communication > > Please add a comment to the ticket saying that you reviewed the > proposal, or please send me your comments. > > Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 > > Thanks, > .Erez > > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > _______________________________________________ > mpi-22 mailing list > mpi-22_at_[hidden] > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22 --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. *

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 08 Dec '08

08 Dec '08

Dear Erez, Thank you. I hope to have replied to your first question in my reply to Dick. It also contains a couple of other concerns I have identified so far in connection to ##45 and 46. The review process definition - and Bill's clarification - are very helpful. I apparently missed this aspect because I did not attend the last meeting. It would be great to have those procedural decision communicated clearly to the Forum in some way after the meeting for the benefit of the absentees. Basing on this definition, I agree that it will be correct to decouple the textual review from the substance discussion of ##45 and 46 that I started - without diminishing the import of either, of course. I'm looking forward to the member's reaction to those concerns that I raised. I become more and more convinced that the proposed changes are going to harm more than they help. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Monday, December 08, 2008 10:12 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Alexander, As far as I recall memory remapping from the main processor to a network device was discussed before (If I recall correctly, in the April meeting). I think that it's close enough to your scenario of remapping to a different process for the purpose of this discussion. Is your case real? Do you know of systems that do that with MPI? Or is it a hypothetical case? For the review process, we do need people to review the text; we added this requirement in the last meeting. Regardless, it does not prevent any other person from giving feedback on the proposal. I'm sure that Jeff or Bill can give you're a more formal definition of the review process. The wiki page state that: https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow * To advance to the first reading, a proposal must be reviewed by the lead chapter author and three other reviewers. That review should check the change against the standard text to ensure that the change in context is correct; in addition, the change should be evaluated for completeness. For changes that involve multiple chapters (but are logically related and hence belong in a single ticket), the respective chapter authors must review the changes in their chapters. These reviews must be entered as comments on the ticket. MPI 2.2 Chapter Authors<https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/MPI2.2ChapterAuthors> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Saturday, December 06, 2008 11:44 AM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I agree to respectfully disagree on this with you, for the following two reasons: 1) The memory remapping scenario IO brought up a couple of days ago was not discussed before the first voting as far as I can recall. If you have proof to the contrary, I would most kindly ask you to present it. If this cannot be done, I would say that a new issue has been added to the discussion, and we may need to review its substance. 2) Next, I would like to see the definition of the ticket review process that states the reviewers are supposed to only check the proposed text for correspondence with the existing standard. My opinion is that reviewers are there to bring both textual and substantial concerns up when they see the need for this. So far I've been acting on this conviction. I'm looking forward to the further discussion on the floor. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Saturday, December 06, 2008 7:45 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Thanks Alexander, I respectfully decline your proposal to suspend the review of these tickets. I don't see any specific reference wrt text in your comments; and you don't bring any new issue that has not been discussed before the 1st voting. Thus I don't see any reason to suspend their review. Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 4:19 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I reviewed the text and found that further polishing of its textual aspects should be suspended until the substance is clarified. I put a comment to this effect into the ticket, as well as into the dependent ticket #46. In my opinion, both tickets are not yet ready to go into the standard and should go into another round of contemplation of their possible repercussions. In both cases presumed application friendliness is traded for less freedom of implementation. Application developers who disregard the standard now will most likely continue to do this in the future, possibly in some other way. Restricting the freedom of implementation to make their life easier does not seem to be an attractive proposition to me. If any of the issues identified so far, or comparable issues we cannot fathom at the moment, surface up in one of the future HPC platforms and hinder MPI adoption or transition to MPI-2.2 there, we will have done disservice both to the MPI standard and to the community. I hope this will bear on the minds of those who're going to vote on these two items at the meeting. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Saturday, December 06, 2008 12:28 AM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Alexander, It is okay and encouraged for people to comment and argue on the proposals. You can add your comments to the ticket arguing your important points. The forum then consider that various points and vote on the proposal. However for the voting process we need people to review the text and confirm that it does not conflict with the standard and it is reasonable (from language pov) to be included in the standard. If we are willing to review the text and state that it valid for the standard, that would be great. If you have any comments on the text please send them to me. Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 2:26 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I'm afraid I would need to have it explained in more detail why review may not include arguments on the substance. If something in the proposal makes one think that the proposed matter may be detrimental to the MPI standard and its implementations, I consider it one's duty to point this out. Following up on your reply: the segfault situation you described will make an MPI compliant program break. Thus, the implementation will have to keep the send buffer mapped into the sending process address space. This is a limitation on the MPI implementation that should be taken into account during the voting. Another possibility that has been pointed out earlier was that the proposed change disallows byte swap and other send buffer conversions to be done in place. At least one historical MPI implementation was doing this to a great avail. Who knows what is going to happen in the future? Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Friday, December 05, 2008 11:18 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) I think that the idea is for the reviewers to check the text for any mistakes and compatibility with the existing text, rather than check for the validity of the proposal. The later as I recall is left for the MPI forum assembly. As for your question, I'm sure that you can answer it yourself. :) If the memory is still also mapped to the original process (as with shared memory) that everything is fine. If the memory is removed from the original process, than the app will get an access-violation fault. (if this system works on a page boundary, to take this action it needs to make sure that there are no other allocation on the same page) Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 2:05 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Hi, I'd like to review this proposal. Let's consider the following scenario: - In the MPI_Isend, MPI maps the send buffer into the address space of the receiving process. - In the matching MPI_Recv, the receiving process makes a copy of the mapped send buffer into the receive buffer. - Once the copy is complete, the send buffer is mapped back into the sender address space during the wait/test call. What will happen one tries to access the send buffer in between? Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Friday, December 05, 2008 10:48 PM To: MPI 2.2 Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) This proposal has passed 1st voting and needs reviewers. We need 3 volunteers to sign-off on this proposal, plus the 3 chapter authors to sign-off on the text. The Chapter Authors for Chapter 3: Point-to-Point Communication Chapter 5: Collective Communication Chapter 11: One-Sided Communication Please add a comment to the ticket saying that you reviewed the proposal, or please send me your comments. Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 Thanks, .Erez --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. *

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 08 Dec '08

08 Dec '08

Dear Dick, Thank you. Keeping the send buffer mapped upon the sender address space is surely legal. I wonder what will be happening to the sender that has, say, thousands of the outstanding MPI_Isends, all of which mapped their contents to the receiver memory. This will consume kernel memory space and possibly hardware resources. Will this be good for scalability? On a microkernel with so little memory to play with? I'd rather map the send buffer out. As for the send or receive side byte swapping, or, for that matter, any kind of reversible transformation - the receiver will certainly do this once. Note however that proposal #46 talks about collectives as well. If there are several receivers in a Bcast type operation, they will all be doing the transformation instead of the sender doing this once there and back again. The total expense will be higher for the receiver side transformation if more than two receivers are involved. Another couple of scenarios to consider: 3) Imagine send buffers have to pinned in the memory. To avoid doing this too often, these registrations will normally be cached. If more than one send can be used for a buffer or, for that matter, overlapping portions of the same buffer, say by different threads, access to the lookup-and-pin will have to be made atomic. This will further complicate implementation and introduce a potentially costly mutual exclusion primitive into the critical path. 4) I wonder what a const modifier will do for a buffer identifies by MPI_BOTTOM and/or a derived data type, possibly with holes in it. How will this square up with the C language sequence association rules? 5) Note also if both #45 and #46 will be introduced, there will be no way to retract this, even with the help of the MPI_INIT_ASSERTED, should we later decide to introduce assertion like MPI_NO_SEND_BUFFER_READ_ACCESS. The const modifier from #46 will make that syntactically useless. 6) Finally, what will happen in the Fortran interface? With the copy-in/copy-out possibly happening on the MPI subroutine boundary for array sections? If more than one send is allowed, the application can pretty easily exhaust any virtual memory with a couple of long enough vectors. I'm looking forward to your and everybody's opinion on those scenarios. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Monday, December 08, 2008 10:56 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) On a single OS under AIX, IBM MPI does map the portion of send side memory that holds the send buffer into the receivers address space. We do this for both contiguous and non-contiguous buffers. The mapping lasts just long enough for the receive side CPU to do a memory copy from send buffer to receive buffer. (see patent 7,392,256) This optimization does not have any effect on the addressability of the send buffer by the sending task. In our case, at least, this optimization does not argue against the proposal. Also, Robert and I had a chat about the byte swap trick and it seems it should be both semantically cleaner and require fewer CPU cycles to do it in the receive buffer. In the receive buffer there is no question that the application must wait for the communication to complete and the swap only needs to be done once (the message flows in with bytes in sender order and the MPI_Recv does one pass of byte swaps if required. In the send buffer trick, the swaps to receiver order must be done and then a second pass is needed to undo it) Dick Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 12/08/2008 04:11:45 PM: > [image removed] > > Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Erez Haba > > to: > > MPI 2.2 > > 12/08/2008 04:13 PM > > Sent by: > > mpi-22-bounces_at_[hidden] > > Please respond to "MPI 2.2" > > Dear Alexander, > > As far as I recall memory remapping from the main processor to a > network device was discussed before (If I recall correctly, in the > April meeting). I think that it's close enough to your scenario of > remapping to a different process for the purpose of this discussion. > > Is your case real? Do you know of systems that do that with MPI? Or > is it a hypothetical case? > > > For the review process, we do need people to review the text; we > added this requirement in the last meeting. Regardless, it does not > prevent any other person from giving feedback on the proposal. I'm > sure that Jeff or Bill can give you're a more formal definition of > the review process. > > The wiki page state that: > https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow > To advance to the first reading, a proposal must be reviewed by the > lead chapter author and three other reviewers. That review should > check the change against the standard text to ensure that the change > in context is correct; in addition, the change should be evaluated > for completeness. For changes that involve multiple chapters (but > are logically related and hence belong in a single ticket), the > respective chapter authors must review the changes in their > chapters. These reviews must be entered as comments on the ticket. > MPI 2.2 Chapter Authors > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Saturday, December 06, 2008 11:44 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I agree to respectfully disagree on this with you, for > the following two reasons: > > 1) The memory remapping scenario IO brought up a couple of days ago > was not discussed before the first voting as far as I can recall. If > you have proof to the contrary, I would most kindly ask you to > present it. If this cannot be done, I would say that a new issue has > been added to the discussion, and we may need to review its substance. > > 2) Next, I would like to see the definition of the ticket review > process that states the reviewers are supposed to only check the > proposed text for correspondence with the existing standard. My > opinion is that reviewers are there to bring both textual and > substantial concerns up when they see the need for this. So far I've > been acting on this conviction. > > I'm looking forward to the further discussion on the floor. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 7:45 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Thanks Alexander, > > I respectfully decline your proposal to suspend the review of these tickets. > I don't see any specific reference wrt text in your comments; and > you don't bring any new issue that has not been discussed before the 1st > voting. Thus I don't see any reason to suspend their review. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 4:19 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I reviewed the text and found that further polishing of > its textual aspects should be suspended until the substance is > clarified. I put a comment to this effect into the ticket, as well > as into the dependent ticket #46. In my opinion, both tickets are > not yet ready to go into the standard and should go into another > round of contemplation of their possible repercussions. > > In both cases presumed application friendliness is traded for less > freedom of implementation. Application developers who disregard the > standard now will most likely continue to do this in the future, > possibly in some other way. Restricting the freedom of > implementation to make their life easier does not seem to be an > attractive proposition to me. > > If any of the issues identified so far, or comparable issues we > cannot fathom at the moment, surface up in one of the future HPC > platforms and hinder MPI adoption or transition to MPI-2.2 there, we > will have done disservice both to the MPI standard and to the > community. I hope this will bear on the minds of those who're going > to vote on these two items at the meeting. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 12:28 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Dear Alexander, > > It is okay and encouraged for people to comment and argue on the > proposals. You can add your comments to the ticket arguing your > important points. The forum then consider that various points and > vote on the proposal. > > However for the voting process we need people to review the text and > confirm that it does not conflict with the standard and it is > reasonable (from language pov) to be included in the standard. > > If we are willing to review the text and state that it valid for the > standard, that would be great. If you have any comments on the text > please send them to me. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:26 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I'm afraid I would need to have it explained in more > detail why review may not include arguments on the substance. If > something in the proposal makes one think that the proposed matter > may be detrimental to the MPI standard and its implementations, I > consider it one's duty to point this out. > > Following up on your reply: the segfault situation you described > will make an MPI compliant program break. Thus, the implementation > will have to keep the send buffer mapped into the sending process > address space. This is a limitation on the MPI implementation that > should be taken into account during the voting. > > Another possibility that has been pointed out earlier was that the > proposed change disallows byte swap and other send buffer > conversions to be done in place. At least one historical MPI > implementation was doing this to a great avail. Who knows what is > going to happen in the future? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 11:18 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > I think that the idea is for the reviewers to check the text for any > mistakes and compatibility with the existing text, rather than check > for the validity of the proposal. The later as I recall is left for > the MPI forum assembly. > > As for your question, I'm sure that you can answer it yourself. J If > the memory is still also mapped to the original process (as with > shared memory) that everything is fine. If the memory is removed > from the original process, than the app will get an access-violation fault. > (if this system works on a page boundary, to take this action it > needs to make sure that there are no other allocation on the same page) > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:05 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Hi, > > I'd like to review this proposal. Let's consider the following scenario: > > - In the MPI_Isend, MPI maps the send buffer into the address space > of the receiving process. > - In the matching MPI_Recv, the receiving process makes a copy of > the mapped send buffer into the receive buffer. > - Once the copy is complete, the send buffer is mapped back into the > sender address space during the wait/test call. > > What will happen one tries to access the send buffer in between? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 10:48 PM > To: MPI 2.2 > Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) > This proposal has passed 1st voting and needs reviewers. We need 3 volunteers > to sign-off on this proposal, plus the 3 chapter authors to sign-off > on the text. > > The Chapter Authors for > > Chapter 3: Point-to-Point Communication > Chapter 5: Collective Communication > Chapter 11: One-Sided Communication > > Please add a comment to the ticket saying that you reviewed the > proposal, or please send me your comments. > > Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 > > Thanks, > .Erez > > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > _______________________________________________ > mpi-22 mailing list > mpi-22_at_[hidden] > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22 --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. *

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 08 Dec '08

08 Dec '08

Thanks Dick, Yes, it makes sense that the send buffer would still be addressable by the sender process as the buffer might share the pages with other memory allocations. (I assume that the mapping is done in page granularity). Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Monday, December 08, 2008 1:56 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) On a single OS under AIX, IBM MPI does map the portion of send side memory that holds the send buffer into the receivers address space. We do this for both contiguous and non-contiguous buffers. The mapping lasts just long enough for the receive side CPU to do a memory copy from send buffer to receive buffer. (see patent 7,392,256) This optimization does not have any effect on the addressability of the send buffer by the sending task. In our case, at least, this optimization does not argue against the proposal. Also, Robert and I had a chat about the byte swap trick and it seems it should be both semantically cleaner and require fewer CPU cycles to do it in the receive buffer. In the receive buffer there is no question that the application must wait for the communication to complete and the swap only needs to be done once (the message flows in with bytes in sender order and the MPI_Recv does one pass of byte swaps if required. In the send buffer trick, the swaps to receiver order must be done and then a second pass is needed to undo it) Dick Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 12/08/2008 04:11:45 PM: > [image removed] > > Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Erez Haba > > to: > > MPI 2.2 > > 12/08/2008 04:13 PM > > Sent by: > > mpi-22-bounces_at_[hidden] > > Please respond to "MPI 2.2" > > Dear Alexander, > > As far as I recall memory remapping from the main processor to a > network device was discussed before (If I recall correctly, in the > April meeting). I think that itâs close enough to your scenario of > remapping to a different process for the purpose of this discussion. > > Is your case real? Do you know of systems that do that with MPI? Or > is it a hypothetical case? > > > For the review process, we do need people to review the text; we > added this requirement in the last meeting. Regardless, it does not > prevent any other person from giving feedback on the proposal. Iâm > sure that Jeff or Bill can give youâre a more formal definition of > the review process. > > The wiki page state that: > https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow > To advance to the first reading, a proposal must be reviewed by the > lead chapter author and three other reviewers. That review should > check the change against the standard text to ensure that the change > in context is correct; in addition, the change should be evaluated > for completeness. For changes that involve multiple chapters (but > are logically related and hence belong in a single ticket), the > respective chapter authors must review the changes in their > chapters. These reviews must be entered as comments on the ticket. > MPI 2.2 Chapter Authors > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Saturday, December 06, 2008 11:44 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I agree to respectfully disagree on this with you, for > the following two reasons: > > 1) The memory remapping scenario IO brought up a couple of days ago > was not discussed before the first voting as far as I can recall. If > you have proof to the contrary, I would most kindly ask you to > present it. If this cannot be done, I would say that a new issue has > been added to the discussion, and we may need to review its substance. > > 2) Next, I would like to see the definition of the ticket review > process that states the reviewers are supposed to only check the > proposed text for correspondence with the existing standard. My > opinion is that reviewers are there to bring both textual and > substantial concerns up when they see the need for this. So far I've > been acting on this conviction. > > I'm looking forward to the further discussion on the floor. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 7:45 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Thanks Alexander, > > I respectfully decline your proposal to suspend the review of these tickets. > I donât see any specific reference wrt text in your comments; and > you donât bring any new issue that has not been discussed before the 1st > voting. Thus I donât see any reason to suspend their review. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 4:19 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I reviewed the text and found that further polishing of > its textual aspects should be suspended until the substance is > clarified. I put a comment to this effect into the ticket, as well > as into the dependent ticket #46. In my opinion, both tickets are > not yet ready to go into the standard and should go into another > round of contemplation of their possible repercussions. > > In both cases presumed application friendliness is traded for less > freedom of implementation. Application developers who disregard the > standard now will most likely continue to do this in the future, > possibly in some other way. Restricting the freedom of > implementation to make their life easier does not seem to be an > attractive proposition to me. > > If any of the issues identified so far, or comparable issues we > cannot fathom at the moment, surface up in one of the future HPC > platforms and hinder MPI adoption or transition to MPI-2.2 there, we > will have done disservice both to the MPI standard and to the > community. I hope this will bear on the minds of those who're going > to vote on these two items at the meeting. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 12:28 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Dear Alexander, > > It is okay and encouraged for people to comment and argue on the > proposals. You can add your comments to the ticket arguing your > important points. The forum then consider that various points and > vote on the proposal. > > However for the voting process we need people to review the text and > confirm that it does not conflict with the standard and it is > reasonable (from language pov) to be included in the standard. > > If we are willing to review the text and state that it valid for the > standard, that would be great. If you have any comments on the text > please send them to me. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:26 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I'm afraid I would need to have it explained in more > detail why review may not include arguments on the substance. If > something in the proposal makes one think that the proposed matter > may be detrimental to the MPI standard and its implementations, I > consider it one's duty to point this out. > > Following up on your reply: the segfault situation you described > will make an MPI compliant program break. Thus, the implementation > will have to keep the send buffer mapped into the sending process > address space. This is a limitation on the MPI implementation that > should be taken into account during the voting. > > Another possibility that has been pointed out earlier was that the > proposed change disallows byte swap and other send buffer > conversions to be done in place. At least one historical MPI > implementation was doing this to a great avail. Who knows what is > going to happen in the future? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 11:18 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > I think that the idea is for the reviewers to check the text for any > mistakes and compatibility with the existing text, rather than check > for the validity of the proposal. The later as I recall is left for > the MPI forum assembly. > > As for your question, Iâm sure that you can answer it yourself. J If > the memory is still also mapped to the original process (as with > shared memory) that everything is fine. If the memory is removed > from the original process, than the app will get an access-violation fault. > (if this system works on a page boundary, to take this action it > needs to make sure that there are no other allocation on the same page) > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:05 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Hi, > > I'd like to review this proposal. Let's consider the following scenario: > > - In the MPI_Isend, MPI maps the send buffer into the address space > of the receiving process. > - In the matching MPI_Recv, the receiving process makes a copy of > the mapped send buffer into the receive buffer. > - Once the copy is complete, the send buffer is mapped back into the > sender address space during the wait/test call. > > What will happen one tries to access the send buffer in between? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 10:48 PM > To: MPI 2.2 > Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) > This proposal has passed 1st voting and needs reviewers. We need 3 volunteers > to sign-off on this proposal, plus the 3 chapter authors to sign-off > on the text. > > The Chapter Authors for > > Chapter 3: Point-to-Point Communication > Chapter 5: Collective Communication > Chapter 11: One-Sided Communication > > Please add a comment to the ticket saying that you reviewed the > proposal, or please send me your comments. > > Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 > > Thanks, > .Erez > > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052 > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > _______________________________________________ > mpi-22 mailing list > mpi-22_at_[hidden] > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22 *

1 0

Voting and review process reminders
by unknown＠example.com 08 Dec '08

08 Dec '08

Here is a reminder of the process for voting and reviews: Votes are taken to approve a change or addition. Votes are taken twice at separate meetings; one reason for the two votes is to allow time for reflection and for additional issues to be raised. It is acceptable to vote yes on one of the two votes and no on the other. Reviews of the proposed text are used to ensure that the text is consistent with the rest of the document. Such reviews do not review the proposal on its own technical grounds (that should be done by the Forum members prior to each vote). Rather, they look for editing errors or inconsistencies with respect to the existing document. As an example of an editing error, when reviewing one proposal that included the LaTeX source (which is to be encourage), there was a use of \mpi/ where \MPI/ was intended. As an example of an inconsistency, in reviewing ticket 55, I noticed that the proposed change was inconsistent with text already in the document. While it is hoped that such inconsistencies would be detected by the Forum members prior to the votes, the review process provides an additional check. Bill William Gropp Deputy Director for Research Institute for Advanced Computing Applications and Technologies Paul and Cynthia Saylor Professor of Computer Science University of Illinois Urbana-Champaign

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 08 Dec '08

08 Dec '08

On a single OS under AIX, IBM MPI does map the portion of send side memory that holds the send buffer into the receivers address space. We do this for both contiguous and non-contiguous buffers. The mapping lasts just long enough for the receive side CPU to do a memory copy from send buffer to receive buffer. (see patent 7,392,256), This optimization does not have any effect on the addressability of the send buffer by the sending task. In our case, at least, this optimization does not argue against the proposal. Also, Robert and I had a chat about the byte swap trick and it seems it should be both semantically cleaner and require fewer CPU cycles to do it in the receive buffer. In the receive buffer there is no question that the application must wait for the communication to complete and the swap only needs to be done once (the message flows in with bytes in sender order and the MPI_Recv does one pass of byte swaps if required. In the send buffer trick, the swaps to receiver order must be done and then a second pass is needed to undo it) Dick Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 12/08/2008 04:11:45 PM: > [image removed] > > Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Erez Haba > > to: > > MPI 2.2 > > 12/08/2008 04:13 PM > > Sent by: > > mpi-22-bounces_at_[hidden] > > Please respond to "MPI 2.2" > > Dear Alexander, > > As far as I recall memory remapping from the main processor to a > network device was discussed before (If I recall correctly, in the > April meeting). I think that itâs close enough to your scenario of > remapping to a different process for the purpose of this discussion. > > Is your case real? Do you know of systems that do that with MPI? Or > is it a hypothetical case? > > > For the review process, we do need people to review the text; we > added this requirement in the last meeting. Regardless, it does not > prevent any other person from giving feedback on the proposal. Iâm > sure that Jeff or Bill can give youâre a more formal definition of > the review process. > > The wiki page state that: > https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow > To advance to the first reading, a proposal must be reviewed by the > lead chapter author and three other reviewers. That review should > check the change against the standard text to ensure that the change > in context is correct; in addition, the change should be evaluated > for completeness. For changes that involve multiple chapters (but > are logically related and hence belong in a single ticket), the > respective chapter authors must review the changes in their > chapters. These reviews must be entered as comments on the ticket. > MPI 2.2 Chapter Authors > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Saturday, December 06, 2008 11:44 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I agree to respectfully disagree on this with you, for > the following two reasons: > > 1) The memory remapping scenario IO brought up a couple of days ago > was not discussed before the first voting as far as I can recall. If > you have proof to the contrary, I would most kindly ask you to > present it. If this cannot be done, I would say that a new issue has > been added to the discussion, and we may need to review its substance. > > 2) Next, I would like to see the definition of the ticket review > process that states the reviewers are supposed to only check the > proposed text for correspondence with the existing standard. My > opinion is that reviewers are there to bring both textual and > substantial concerns up when they see the need for this. So far I've > been acting on this conviction. > > I'm looking forward to the further discussion on the floor. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 7:45 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Thanks Alexander, > > I respectfully decline your proposal to suspend the review of these tickets. > I donât see any specific reference wrt text in your comments; and > you donât bring any new issue that has not been discussed before the 1st > voting. Thus I donât see any reason to suspend their review. > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 4:19 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I reviewed the text and found that further polishing of > its textual aspects should be suspended until the substance is > clarified. I put a comment to this effect into the ticket, as well > as into the dependent ticket #46. In my opinion, both tickets are > not yet ready to go into the standard and should go into another > round of contemplation of their possible repercussions. > > In both cases presumed application friendliness is traded for less > freedom of implementation. Application developers who disregard the > standard now will most likely continue to do this in the future, > possibly in some other way. Restricting the freedom of > implementation to make their life easier does not seem to be an > attractive proposition to me. > > If any of the issues identified so far, or comparable issues we > cannot fathom at the moment, surface up in one of the future HPC > platforms and hinder MPI adoption or transition to MPI-2.2 there, we > will have done disservice both to the MPI standard and to the > community. I hope this will bear on the minds of those who're going > to vote on these two items at the meeting. > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Saturday, December 06, 2008 12:28 AM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > Dear Alexander, > > It is okay and encouraged for people to comment and argue on the > proposals. You can add your comments to the ticket arguing your > important points. The forum then consider that various points and > vote on the proposal. > > However for the voting process we need people to review the text and > confirm that it does not conflict with the standard and it is > reasonable (from language pov) to be included in the standard. > > If we are willing to review the text and state that it valid for the > standard, that would be great. If you have any comments on the text > please send them to me.) > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:26 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Dear Erez, > > Thank you. I'm afraid I would need to have it explained in more > detail why review may not include arguments on the substance. If > something in the proposal makes one think that the proposed matter > may be detrimental to the MPI standard and its implementations, I > consider it one's duty to point this out. > > Following up on your reply: the segfault situation you described > will make an MPI compliant program break. Thus, the implementation > will have to keep the send buffer mapped into the sending process > address space. This is a limitation on the MPI implementation that > should be taken into account during the voting. > > Another possibility that has been pointed out earlier was that the > proposed change disallows byte swap and other send buffer > conversions to be done in place. At least one historical MPI > implementation was doing this to a great avail. Who knows what is > going to happen in the future? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 11:18 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > I think that the idea is for the reviewers to check the text for any > mistakes and compatibility with the existing text, rather than check > for the validity of the proposal. The later as I recall is left for > the MPI forum assembly. > > As for your question, Iâm sure that you can answer it yourself. J If > the memory is still also mapped to the original process (as with > shared memory) that everything is fine. If the memory is removed > from the original process, than the app will get an access-violation fault. > (if this system works on a page boundary, to take this action it > needs to make sure that there are no other allocation on the same page) > > Thanks, > .Erez > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Supalov, Alexander > Sent: Friday, December 05, 2008 2:05 PM > To: MPI 2.2 > Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) > > Hi, > > I'd like to review this proposal. Let's consider the following scenario:. > > - In the MPI_Isend, MPI maps the send buffer into the address space > of the receiving process. > - In the matching MPI_Recv, the receiving process makes a copy of > the mapped send buffer into the receive buffer. > - Once the copy is complete, the send buffer is mapped back into the > sender address space during the wait/test call. > > What will happen one tries to access the send buffer in between? > > Best regards. > > Alexander > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Erez Haba > Sent: Friday, December 05, 2008 10:48 PM > To: MPI 2.2 > Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) > This proposal has passed 1st voting and needs reviewers. We need 3 volunteers > to sign-off on this proposal, plus the 3 chapter authors to sign-off > on the text. > > The Chapter Authors for > > Chapter 3: Point-to-Point Communication > Chapter 5: Collective Communication > Chapter 11: One-Sided Communication > > Please add a comment to the ticket saying that you reviewed the > proposal, or please send me your comments., > > Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 > > Thanks, > .Erez > > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052. > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052. > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052. > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > --------------------------------------------------------------------- > Intel GmbH > Dornacher Strasse 1 > 85622 Feldkirchen/Muenchen Germany > Sitz der Gesellschaft: Feldkirchen bei Muenchen > Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer > Registergericht: Muenchen HRB 47456 Ust.-IdNr. > VAT Registration No.: DE129385895 > Citibank Frankfurt (BLZ 502 109 00) 600119052. > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > _______________________________________________ > mpi-22 mailing list > mpi-22_at_[hidden] > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22 *

1 0

Re: [Mpi-22] please review - Send Buffer Access (ticket #45)
by unknown＠example.com 08 Dec '08

08 Dec '08

Dear Alexander, As far as I recall memory remapping from the main processor to a network device was discussed before (If I recall correctly, in the April meeting). I think that it's close enough to your scenario of remapping to a different process for the purpose of this discussion. Is your case real? Do you know of systems that do that with MPI? Or is it a hypothetical case? For the review process, we do need people to review the text; we added this requirement in the last meeting. Regardless, it does not prevent any other person from giving feedback on the proposal. I'm sure that Jeff or Bill can give you're a more formal definition of the review process. The wiki page state that: https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/TicketWorkflow * To advance to the first reading, a proposal must be reviewed by the lead chapter author and three other reviewers. That review should check the change against the standard text to ensure that the change in context is correct; in addition, the change should be evaluated for completeness. For changes that involve multiple chapters (but are logically related and hence belong in a single ticket), the respective chapter authors must review the changes in their chapters. These reviews must be entered as comments on the ticket. MPI 2.2 Chapter Authors<https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/MPI2.2ChapterAuthors> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Saturday, December 06, 2008 11:44 AM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I agree to respectfully disagree on this with you, for the following two reasons: 1) The memory remapping scenario IO brought up a couple of days ago was not discussed before the first voting as far as I can recall. If you have proof to the contrary, I would most kindly ask you to present it. If this cannot be done, I would say that a new issue has been added to the discussion, and we may need to review its substance. 2) Next, I would like to see the definition of the ticket review process that states the reviewers are supposed to only check the proposed text for correspondence with the existing standard. My opinion is that reviewers are there to bring both textual and substantial concerns up when they see the need for this. So far I've been acting on this conviction. I'm looking forward to the further discussion on the floor. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Saturday, December 06, 2008 7:45 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Thanks Alexander, I respectfully decline your proposal to suspend the review of these tickets. I don't see any specific reference wrt text in your comments; and you don't bring any new issue that has not been discussed before the 1st voting. Thus I don't see any reason to suspend their review. Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 4:19 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I reviewed the text and found that further polishing of its textual aspects should be suspended until the substance is clarified. I put a comment to this effect into the ticket, as well as into the dependent ticket #46. In my opinion, both tickets are not yet ready to go into the standard and should go into another round of contemplation of their possible repercussions. In both cases presumed application friendliness is traded for less freedom of implementation. Application developers who disregard the standard now will most likely continue to do this in the future, possibly in some other way. Restricting the freedom of implementation to make their life easier does not seem to be an attractive proposition to me. If any of the issues identified so far, or comparable issues we cannot fathom at the moment, surface up in one of the future HPC platforms and hinder MPI adoption or transition to MPI-2.2 there, we will have done disservice both to the MPI standard and to the community. I hope this will bear on the minds of those who're going to vote on these two items at the meeting. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Saturday, December 06, 2008 12:28 AM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Alexander, It is okay and encouraged for people to comment and argue on the proposals. You can add your comments to the ticket arguing your important points. The forum then consider that various points and vote on the proposal. However for the voting process we need people to review the text and confirm that it does not conflict with the standard and it is reasonable (from language pov) to be included in the standard. If we are willing to review the text and state that it valid for the standard, that would be great. If you have any comments on the text please send them to me. Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 2:26 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Dear Erez, Thank you. I'm afraid I would need to have it explained in more detail why review may not include arguments on the substance. If something in the proposal makes one think that the proposed matter may be detrimental to the MPI standard and its implementations, I consider it one's duty to point this out. Following up on your reply: the segfault situation you described will make an MPI compliant program break. Thus, the implementation will have to keep the send buffer mapped into the sending process address space. This is a limitation on the MPI implementation that should be taken into account during the voting. Another possibility that has been pointed out earlier was that the proposed change disallows byte swap and other send buffer conversions to be done in place. At least one historical MPI implementation was doing this to a great avail. Who knows what is going to happen in the future? Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Friday, December 05, 2008 11:18 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) I think that the idea is for the reviewers to check the text for any mistakes and compatibility with the existing text, rather than check for the validity of the proposal. The later as I recall is left for the MPI forum assembly. As for your question, I'm sure that you can answer it yourself. :) If the memory is still also mapped to the original process (as with shared memory) that everything is fine. If the memory is removed from the original process, than the app will get an access-violation fault. (if this system works on a page boundary, to take this action it needs to make sure that there are no other allocation on the same page) Thanks, .Erez From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander Sent: Friday, December 05, 2008 2:05 PM To: MPI 2.2 Subject: Re: [Mpi-22] please review - Send Buffer Access (ticket #45) Hi, I'd like to review this proposal. Let's consider the following scenario: - In the MPI_Isend, MPI maps the send buffer into the address space of the receiving process. - In the matching MPI_Recv, the receiving process makes a copy of the mapped send buffer into the receive buffer. - Once the copy is complete, the send buffer is mapped back into the sender address space during the wait/test call. What will happen one tries to access the send buffer in between? Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba Sent: Friday, December 05, 2008 10:48 PM To: MPI 2.2 Subject: [Mpi-22] please review - Send Buffer Access (ticket #45) This proposal has passed 1st voting and needs reviewers. We need 3 volunteers to sign-off on this proposal, plus the 3 chapter authors to sign-off on the text. The Chapter Authors for Chapter 3: Point-to-Point Communication Chapter 5: Collective Communication Chapter 11: One-Sided Communication Please add a comment to the ticket saying that you reviewed the proposal, or please send me your comments. Send Buffer Access: https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/45 Thanks, .Erez --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. *

1 0