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

Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 09 May '08

09 May '08

I think Alexander hit on the answer to this: how is the user to know what is going to offer an implementation some advantage? What may look like it could offer a lot of benefit from a users perspective (ready send) could be considered low priority by the implementer. Especially in the constrained environments example, every implementer for a constrained environment could have a different perception of what they can make fast and small. So, an application that runs fine on a Cell SPE could blow up the code memory footprint on a Clearspeed. This is ultimately bad for the user. That is to say nothing of the dynamic memory footprint, which I am sure an implementer could trim with appropriate guarantees. I'm not sure official subsetting is the right answer or what the right approach for getting that functionality would be, but I am pretty sure that MPI on a Cell SPE is going to be a subset - whether it is official or not :-) Keith ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Friday, May 09, 2008 3:48 PM To: MPI 2.2 Subject: Re: [Mpi-22] Memory footprint concern Hi Keith Say the MPI implementor for the Cell SPE version of MPI did a good job of organizing his functionality (perhaps by making subsetting decisions that work for the structure of his implementation). Say there is an MPI application that only makes calls to the 6 essential MPI routines plus MPI_Allreduce and MPI_Bcast. When that application is statically bound to the MPI implementation by a smart linker that follows dependancy chains and only brings in needed subroutines don't you get the desired result? What more do you get in this case from having the MPI standard dictate the subsets and asking the user to declare what subsets he will need? If you leave it to the implementor to devise the subsets and change them as some ways of slicing and dicing libmpi prove more useful than others it may be better than having the standard lock down the dividing lines based on today's best guess. It does occur to me that the linker cannot tell if the MPI_Bcast call will need the code that supports MPI_Bcast on intercommunicators even though that is rarely used. That means if the application has an MPI_Bcast call, both (probably needed) intracomm- and (probably not needed) intercomm support enter the footprint. Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 05/09/2008 02:34:33 PM: > Imagine, for example, MPI running on a Cell SPE. Yes, it sounds > crazy, but people are working on it. If you look at the state in > MPI-2 today, and assume it will grow proportionally with complexity, > MPI-3 could be really nasty in that context. So, while I agree that > an arbitrarily large number of permutations is a terrible idea for > everyone involved (implementers wouldn't leverage all of the > options, ISVs wouldn't test them, people who write third party > libraries would have a huge headache dealing with the arbitrary > combination of features chosen by the application), it seems like it > would be prudent to try to figure out how to provide some mechanisms > in this direction. I don't know if this overlaps with your idea > about assertions or not, but they do seem to be related. > > Keith > *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 09 May '08

09 May '08

Hi Keith Say the MPI implementor for the Cell SPE version of MPI did a good job of organizing his functionality (perhaps by making subsetting decisions that work for the structure of his implementation). Say there is an MPI application that only makes calls to the 6 essential MPI routines plus MPI_Allreduce and MPI_Bcast. When that application is statically bound to the MPI implementation by a smart linker that follows dependancy chains and only brings in needed subroutines don't you get the desired result? What more do you get in this case from having the MPI standard dictate the subsets and asking the user to declare what subsets he will need? If you leave it to the implementor to devise the subsets and change them as some ways of slicing and dicing libmpi prove more useful than others it may be better than having the standard lock down the dividing lines based on today's best guess. It does occur to me that the linker cannot tell if the MPI_Bcast call will need the code that supports MPI_Bcast on intercommunicators even though that is rarely used. That means if the application has an MPI_Bcast call, both (probably needed) intracomm- and (probably not needed) intercomm support enter the footprint. Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 05/09/2008 02:34:33 PM: > Imagine, for example, MPI running on a Cell SPE. Yes, it sounds > crazy, but people are working on it. If you look at the state in > MPI-2 today, and assume it will grow proportionally with complexity, > MPI-3 could be really nasty in that context. So, while I agree that > an arbitrarily large number of permutations is a terrible idea for > everyone involved (implementers wouldnât leverage all of the > options, ISVs wouldnât test them, people who write third party > libraries would have a huge headache dealing with the arbitrary > combination of features chosen by the application), it seems like it > would be prudent to try to figure out how to provide some mechanisms > in this direction. I donât know if this overlaps with your idea > about assertions or not, but they do seem to be related. > > Keith > *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 09 May '08

09 May '08

Imagine, for example, MPI running on a Cell SPE. Yes, it sounds crazy, but people are working on it. If you look at the state in MPI-2 today, and assume it will grow proportionally with complexity, MPI-3 could be really nasty in that context. So, while I agree that an arbitrarily large number of permutations is a terrible idea for everyone involved (implementers wouldn't leverage all of the options, ISVs wouldn't test them, people who write third party libraries would have a huge headache dealing with the arbitrary combination of features chosen by the application), it seems like it would be prudent to try to figure out how to provide some mechanisms in this direction. I don't know if this overlaps with your idea about assertions or not, but they do seem to be related. Keith ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Friday, May 09, 2008 3:12 AM To: MPI 2.2 Subject: Re: [Mpi-22] Memory footprint concern Hi Alexander If we would envision defining subsets in such a way that a machine with limited memory per node and un-fancy OS can clearly document what its MPI offers, maybe it is not a huge addition to complexity. For example if an MPI implementation could say it offers subsets: MPI 1.2 MPI-IO MPI-Intercomm Collectives and nothing else and the meaning would be well defined that may not be too bad. If you are expecting such a machine to have all or most of MPI-3 available and each user would select only the parts he wants at job launch time it seems to me the complexity for implementation and testing will be prohibitive. In particular if you hope subsets will give better performance because of what they leave out and really be compact because they leave out most unneeded bytes of code the number of permutations seem to me to make that a vain hope. I have been ambivalent about whether my assertions proposal really has much connection to the subsets concept mostly because I think to be useful assertions must be fairly simple. The only assertion I am 100% sure will pay off and be used is MPI_NO_EAGER_THROTTLE. There are MPI implementations today that act as if the assertion MPI_NO_EAGER_THROTTLE were present on all applications but that is not an option for a vendor MPI because if somebody contacts service and says "Your MPI violates the standard" a vendor like IBM must "fix" it. IBM MPI supports MPI_CANCEL on MPI_ISEND but at least one MPI does not because it is "too expensive". In effect they act like every application has the assertion MPI_NO_SEND_CANCELS. IBM MPI could make use of MPI_NO_REQUEST_MIX if it was available. Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 "Supalov, Alexander" <alexander.supalov_at_[hidden]> "Supalov, Alexander" <alexander.supalov_at_[hidden]> Sent by: mpi-22-bounces_at_[hidden] 05/08/2008 05:52 PM Please respond to "MPI 2.2" <mpi-22_at_[hidden]> To "MPI 2.2" <mpi-22_at_[hidden]> cc Subject Re: [Mpi-22] Memory footprint concern Dear Dick, By the looks of it, MPI-3 is going to be big. Petascale machines may not have OS we're accustomed to, dynamic libraries, and some other things. Smaller system libraries - and smaller MPI - may be needed there. Some of the envisioned MPI-3 features will be needed for some applications, some won't. Same with MPI-2 and MPI-1. Defining subsets may help to open a way to custom cut MPI libraries suitable for particular application classes. How subsets will be implemented is a different matter. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [ mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Thursday, May 08, 2008 11:23 PM To: MPI 2.2 Subject: [Mpi-22] Memory footprint concern Can somebody help me understand this "smaller memory footprint" issue that is part f the subsetting goal better. What systems does it affect? What does "memory footprint" really mean? In the 64 bit address space, virtual address range is not a problem. On systems I am most familiar with (AIX and I have been told Linux too), if you have a library that contains 1000 subroutines and you run a program than only calls 6 then only the pages that are touched by code for those 6 functions must get placed in real memory. The rest of the object code stays on disk. Program and library text is demand paged. The loading is on page boundries, not subroutine boundries. With a shared library, if I run a program on a node and touch 6 subroutines and you run a different program that touches those 6 and 10 more then code for all 16 subroutines may be kept in memory but the rest of the library will stay on disk. You and I will share the object code for the 6 subroutines we are both calling. Someone who wanted to make a libmpi that has MPI-1sided or MPI-IO well isolated in the library structure so simple MPI jobs would not force this extra code into memory could do that today. The user does not need to promise not to call MPI-IO subroutines for them not to to take real memory. The "subsets" would need to be devised by the MPI implementor but would be transparent to the MPI user and not dictated by the standard. The "subsets" the user did not call would remain paged out. Perhaps all static data defined by the library will come into real memory for each process but is there much reduction from being able to somehow not bring in the static data MPI-IO would require because somebody had promised not to use it? Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 --------------------------------------------------------------------- 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 *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 09 May '08

09 May '08

Dear Bill, Thanks. I would agree with you on that subsets are indeed not required, but their clear definition in the standard would promote equally clear and uniform implementation of the memory footprint minimizing approaches you and Dick referred to. I guess static linkage is the easiest case for this, as the linkers are smart enough nowadays to load only the required parts of the library, provided it's appropriately structured. Again, subsets may promote such a structuring. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of William Gropp Sent: Friday, May 09, 2008 2:32 PM To: MPI 2.2 Subject: Re: [Mpi-22] Memory footprint concern On the memory footprint issue, I'd like to add that it is possible to structure an MPI implementation to only require the code associated with the routines that are used in the application, even when the application must be statically linked (as is the case for Blue Gene/L, for example). This can be done even if there are actions that the application needs or wants to perform at the time of MPI_Finalize. There are some things that can be done to make this easier for the implementation, but (like Dick) I'm not convinced that a subset is required as a way to limit the memory footprint. Bill William Gropp Paul and Cynthia Saylor Professor of Computer Science University of Illinois Urbana-Champaign --------------------------------------------------------------------- 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. *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 09 May '08

09 May '08

On the memory footprint issue, I'd like to add that it is possible to structure an MPI implementation to only require the code associated with the routines that are used in the application, even when the application must be statically linked (as is the case for Blue Gene/ L, for example). This can be done even if there are actions that the application needs or wants to perform at the time of MPI_Finalize. There are some things that can be done to make this easier for the implementation, but (like Dick) I'm not convinced that a subset is required as a way to limit the memory footprint. Bill William Gropp Paul and Cynthia Saylor Professor of Computer Science University of Illinois Urbana-Champaign *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 08 May '08

08 May '08

Hi Alexander If we would envision defining subsets in such a way that a machine with limited memory per node and un-fancy OS can clearly document what its MPI offers, maybe it is not a huge addition to complexity. For example if an MPI implementation could say it offers subsets: MPI 1.2 MPI-IO MPI-Intercomm Collectives and nothing else and the meaning would be well defined that may not be too bad. If you are expecting such a machine to have all or most of MPI-3 available and each user would select only the parts he wants at job launch time it seems to me the complexity for implementation and testing will be prohibitive. In particular if you hope subsets will give better performance because of what they leave out and really be compact because they leave out most unneeded bytes of code the number of permutations seem to me to make that a vain hope. I have been ambivalent about whether my assertions proposal really has much connection to the subsets concept mostly because I think to be useful assertions must be fairly simple. The only assertion I am 100% sure will pay off and be used is MPI_NO_EAGER_THROTTLE. There are MPI implementations today that act as if the assertion MPI_NO_EAGER_THROTTLE were present on all applications but that is not an option for a vendor MPI because if somebody contacts service and says "Your MPI violates the standard" a vendor like IBM must "fix" it. IBM MPI supports MPI_CANCEL on MPI_ISEND but at least one MPI does not because it is "too expensive". In effect they act like every application has the assertion MPI_NO_SEND_CANCELS. IBM MPI could make use of MPI_NO_REQUEST_MIX if it was available. Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 "Supalov, Alexander" <alexander.supalo To v_at_[hidden]> "MPI 2.2" Sent by: <mpi-22_at_[hidden]> mpi-22-bounces_at_li cc sts.mpi-forum.org Subject Re: [Mpi-22] Memory footprint 05/08/2008 05:52 concern PM Please respond to "MPI 2.2" <mpi-22_at_lists.mpi -forum.org> Dear Dick, By the looks of it, MPI-3 is going to be big. Petascale machines may not have OS we're accustomed to, dynamic libraries, and some other things. Smaller system libraries - and smaller MPI - may be needed there. Some of the envisioned MPI-3 features will be needed for some applications, some won't. Same with MPI-2 and MPI-1. Defining subsets may help to open a way to custom cut MPI libraries suitable for particular application classes. How subsets will be implemented is a different matter. Best regards. Alexander From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Thursday, May 08, 2008 11:23 PM To: MPI 2.2 Subject: [Mpi-22] Memory footprint concern Can somebody help me understand this "smaller memory footprint" issue that is part f the subsetting goal better. What systems does it affect? What does "memory footprint" really mean? In the 64 bit address space, virtual address range is not a problem. On systems I am most familiar with (AIX and I have been told Linux too), if you have a library that contains 1000 subroutines and you run a program than only calls 6 then only the pages that are touched by code for those 6 functions must get placed in real memory. The rest of the object code stays on disk. Program and library text is demand paged. The loading is on page boundries, not subroutine boundries. With a shared library, if I run a program on a node and touch 6 subroutines and you run a different program that touches those 6 and 10 more then code for all 16 subroutines may be kept in memory but the rest of the library will stay on disk. You and I will share the object code for the 6 subroutines we are both calling. Someone who wanted to make a libmpi that has MPI-1sided or MPI-IO well isolated in the library structure so simple MPI jobs would not force this extra code into memory could do that today. The user does not need to promise not to call MPI-IO subroutines for them not to to take real memory. The "subsets" would need to be devised by the MPI implementor but would be transparent to the MPI user and not dictated by the standard. The "subsets" the user did not call would remain paged out. Perhaps all static data defined by the library will come into real memory for each process but is there much reduction from being able to somehow not bring in the static data MPI-IO would require because somebody had promised not to use it? Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 --------------------------------------------------------------------- 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 *

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Re: [Mpi-22] Memory footprint concern
by unknown＠example.com 08 May '08

08 May '08

Dear Dick, By the looks of it, MPI-3 is going to be big. Petascale machines may not have OS we're accustomed to, dynamic libraries, and some other things. Smaller system libraries - and smaller MPI - may be needed there. Some of the envisioned MPI-3 features will be needed for some applications, some won't. Same with MPI-2 and MPI-1. Defining subsets may help to open a way to custom cut MPI libraries suitable for particular application classes. How subsets will be implemented is a different matter. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Thursday, May 08, 2008 11:23 PM To: MPI 2.2 Subject: [Mpi-22] Memory footprint concern Can somebody help me understand this "smaller memory footprint" issue that is part f the subsetting goal better. What systems does it affect? What does "memory footprint" really mean? In the 64 bit address space, virtual address range is not a problem. On systems I am most familiar with (AIX and I have been told Linux too), if you have a library that contains 1000 subroutines and you run a program than only calls 6 then only the pages that are touched by code for those 6 functions must get placed in real memory. The rest of the object code stays on disk. Program and library text is demand paged. The loading is on page boundries, not subroutine boundries. With a shared library, if I run a program on a node and touch 6 subroutines and you run a different program that touches those 6 and 10 more then code for all 16 subroutines may be kept in memory but the rest of the library will stay on disk. You and I will share the object code for the 6 subroutines we are both calling. Someone who wanted to make a libmpi that has MPI-1sided or MPI-IO well isolated in the library structure so simple MPI jobs would not force this extra code into memory could do that today. The user does not need to promise not to call MPI-IO subroutines for them not to to take real memory. The "subsets" would need to be devised by the MPI implementor but would be transparent to the MPI user and not dictated by the standard. The "subsets" the user did not call would remain paged out. Perhaps all static data defined by the library will come into real memory for each process but is there much reduction from being able to somehow not bring in the static data MPI-IO would require because somebody had promised not to use it? Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 --------------------------------------------------------------------- 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. *

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Memory footprint concern
by unknown＠example.com 08 May '08

08 May '08

Can somebody help me understand this "smaller memory footprint" issue that is part f the subsetting goal better. What systems does it affect? What does "memory footprint" really mean? In the 64 bit address space, virtual address range is not a problem. On systems I am most familiar with (AIX and I have been told Linux too), if you have a library that contains 1000 subroutines and you run a program than only calls 6 then only the pages that are touched by code for those 6 functions must get placed in real memory. The rest of the object code stays on disk. Program and library text is demand paged. The loading is on page boundries, not subroutine boundries. With a shared library, if I run a program on a node and touch 6 subroutines and you run a different program that touches those 6 and 10 more then code for all 16 subroutines may be kept in memory but the rest of the library will stay on disk. You and I will share the object code for the 6 subroutines we are both calling. Someone who wanted to make a libmpi that has MPI-1sided or MPI-IO well isolated in the library structure so simple MPI jobs would not force this extra code into memory could do that today. The user does not need to promise not to call MPI-IO subroutines for them not to to take real memory. The "subsets" would need to be devised by the MPI implementor but would be transparent to the MPI user and not dictated by the standard. The "subsets" the user did not call would remain paged out. Perhaps all static data defined by the library will come into real memory for each process but is there much reduction from being able to somehow not bring in the static data MPI-IO would require because somebody had promised not to use it? Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 *

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Re: [Mpi-22] MPI_INIT assertions
by unknown＠example.com 08 May '08

08 May '08

Hi Alexander First - changing the rules to let MPI_Info objects be created and manipulated before MPI_INIT is much more intrusive on implementations. If the MPI implementation uses some set of data structures to manage MPI opaque objects, those data structures probably do not exist before MPI_INIT. Passing a bit vector into MPI_INIT does not require significant reorganization of the MPI implementation but allowing MPI_Info creation and manipulation does. The concept of an "assertions" bit vector is not new for MPI (see last paragreph) so using it does not require inventing two mechanisms. You have found a couple examples that flirt with violating the concept of a "hint". For soft spawn I would argue that any soft spawn call that would have succeeded as a hard spawn must also succeed as a soft spawn no matter what hint you provide. That is, if you try to spawn with maxprocs=16 and you get 16 task your hint that you would take 8 has not resulted in semantic thin ice. If your hint said you take 32 tasks, MPI can give you 16 and again no semantic thin ice. Even if you ask for 16 on the call but agree to 8 with a hint and a hard spawn for 8 tasks "would have worked", libmpi is free to ignore the hint and fail the call because it cannot provide the 16. On wdir (+ host, arch, path, file) it gets fuzzy. An MPI implementation is free to ignore any of these and the user is free to omit them and hope the MPI implementation has reasonable defaults. It could be argued that the MPI implementation has the option of ignoring a hint when it cannot honor it and falling back to the default. That would fit the "hint" concept but I do not know if that was envisioned when these were put in MPI-2. Actually we may want to look at doing a careful catagorization of the kinds of inputs that an MPI_Info can convey. I may be making assumptions that are not justified by a strict reading of the standard when I imply that MPI_Info (key, value) pairs == hints. As part of MPI 3 we may want to specify that the MPI_Info object can carry several kinds if "info" to an MPI implementation after MPI_INIT. hints - can never break semantic or trigger error messages directives - do not break semantic but can make the difference between a run succeeding and failing (e.g.the named wdir does not exist so libmpi takes an error trying to use it) assertions - can alter semantic. If we want a way to put assertions on communicators for example I see no reason we could not use an Info object to pass them in more? In MPI_FILE_OPEN we have MPI_MODE_UNIQUE_OPEN as a mode flag and say that if the user says MPI_MODE_UNIQUE_OPEN and is wrong, his results cannot be ensured. Silent corruption of the file is possible. We do not use the word "assertion" though maybe we should have. In MPI 1sided synch operations we have an integer IN argument we call an "assertion" and it can take flages like MPI_MODE_NOCHECK, MPI_MODE_NOSTORE or MPI_MODE_NOPUT. We tell the user that if he provides an assertion that is invalid he cannot assume the program will work even though it would have without the assertion. Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 "Supalov, Alexander" <alexander.supalo To v_at_[hidden]> "MPI 2.2" Sent by: <mpi-22_at_[hidden]> mpi-22-bounces_at_li cc sts.mpi-forum.org Subject Re: [Mpi-22] MPI_INIT assertions 05/08/2008 10:52 AM Please respond to "MPI 2.2" <mpi-22_at_lists.mpi -forum.org> Dear Dick, Thank you, I think I start feeling the difference between the assertions and the hints. To be completely sure, where would you put the soft spawning info key: is this an assertion or a hint? What about other standardized info elements that materially influence the program execution or may even predetermine its success or failure (like wdir)? More generally, will the difference between assertions and hints justify the use of two different mechanisms to pass the data across the MPI boundary? Here's I think what we can save by dropping certain MPI features: Dynamic process support: less overhead in the progress engine, easier global rank handling. File I/O: smaller requests, easier wait/test functions. One-sided ops: no passive target w/o MPI calls - no extra progress thread. Communicator & group management: better memory footprint. Non-blocking communication: easier ordering, simplified request handling. Heterogeneity: better memory footprint, easier data handling. Derived datatypes (especially those with holes): better memory footprint. Message tagging: better support for stable dataflow exchanges, smaller packets. Best regards. Alexander From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Tuesday, May 06, 2008 5:21 PM To: MPI 2.2 Subject: Re: [Mpi-22] MPI_INIT assertions In my view, each assertion we define in the standard should be justified by a good explanation of how it allows an MPI implementation to be more efficient and what cost/risk it adds In effect, a cost/benefit analysis. No plausible rationale - no assertion. An assertion is a statement about the application. It is not a request for libmpi to "provide something". In my proposal, an application that correctly uses some assertion must still be written to work on an MPI implementation that ignores that assertion. An application that incorrectly uses some assertion can fail or give wrong answers. You can picture an assertion as the application author granting libmpi permission to "NOT provide something" at the MPI implementors discretion. In MPI 2 we maintained a careful distinction between hints and assertions. The MPI implementation is not allowed to give wrong results or error messages when an application provides an incorrect hint. If an application could provide a hint that it would not use MPI_CANCEL on a particular communicator and then called MPI_CANCEL, it would be OK for libmpi to use a really slow CANCEL protocol but not OK for it to issue a fatal error or ignore the CANCEL. That means that the freedom to "exploit" a hint in libmpi is very limited and less care is required of the user in providing hints. Much of what is being proposed should be treated as hints and could use a different and extensible mechanism. We can consider extending the MPI_Info usage in MPI-3 to address information passing that is hint-like. The MPI standard intends applications to be platform agnostic and source level portable and we should not break that. An assertions interface for making statements about the application will not limit this kind of portability. If there are no MPI_CANCEL calls today, there are no MPI_CANCEL calls after recompilation for a new platform. If we add features for platform tuning (like how many tasks per node or eager threshhold) we could damage portability. In my first outline, I threw in MPI-IO and MPI-1SC without any rationale for how they are useful. You added: "No communicator & group management", "No non-blocking communication", "No message tagging" and "No derived datatypes". It is not clear to me they are all useful so a decent rationale would be needed for each. That makes 6 bits that may be free. The thread support level parameter in MPI_INIT_THREAD is a request to the MPI library to provide some level of thread support and I question how cleanly that maps into the "assertions" model. The assertions model may only require one bit for "MPI_NO_THREAD_CONTENTION". That frees 3 more of the bits you suggest are already taken. If we conclude that all 4 thread support options are really useful it may be best to add the assertions flag to MPI_INIT_THREAD and keep the thread support controls as they are. Even the MPI_NO_THREAD_CONTENTION bit frees up then. My original thought was that we would add a new function that adds a parameter to MPI_INIT_THREAD. I am convinced that the number of assertions defined by the MPI standard should be very limited because each brings some risk and complicates life for library writers. If we end up with as many as 32 assertions I will apologize for having offered the idea in the first place and probably advocate a no vote. If MPI 2.2 provided only MPI_NO_EAGER_THROTTLE, MPI_NO_SEND_CANCEL, MPI_NO_REQUEST_MIX, MPI_NO_ANY_SOURCE and MPI_NO_REDUCTION_ORDER I would be content and debate about adding more could wait for MPI 3.0. The assertion that the application does not try to match persistent send/recv with nonpersistent recv/send would be a nice 2.2 bonus. That accounts for 6 bits. The query function could be something as simple as: MPI_Query_assertions(int *stated, int *exploited) The author of libfred could code in his Init_fred routine: int stated_by_app, exploited_by_lib; MPI_Query_assertions( &stated_by_app, &exploited_by_lib) if (exploited_by_lib & MPI_NO_SEND_CANCEL) fatal_error("Assertion MPI_NO_SEND_CANCEL is not compatable with Fred Lib") else if (stated_by_app & MPI_NO_SEND_CANCEL) warn("Assertion MPI_NO_SEND_CANCEL is not compatable with Fred Lib. It is not exploited by your MPI but your application will not port to an MPI that does exploit MPI_NO_SEND_CANCEL"); If Fred is really cautious he can code If (stated_by_app != 0) fatal_error("Fred does not like assertions") and see if anybody asks for some assertion to be tolerated in the next release of FredLib. You mention "No eager buffering" which is different than what I proposed and is not logically an "assertion". MPI applications should not depend semantically on eager buffering today and the standard is clear that a MPI implementation which has no eager buffering can still be 100% compliant. The standard requires that IF an MPI implementation provides an eager protocol as a performance enhancement, it must also provide a safety feature which can be expensive. Many (perhaps most) applications can benefit from an eager protocol but do not need the safety feature because the application is self regulating. These applications could assert: "I do not require the safety feature." which would allow them the benefit of eager protocol without the costs of the safety feature. I can see a rationale for some kind of hints related to eager protocol buffer space and threshhold. There are many other kinds of granular "hint" support that may be useful but all that should be kept distinct from this proposal (In my opinion). Regards - Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 05/06/2008 07:26:03 AM: > Dear Dick, > > Thanks. What about passing more verbose information to and from an > MPI implementation? Say, eager threshold value, if it's meaningful? > There are many less controversial examples, for example, to let the > caller know how many processes are placed onto the node, etc. Simple > assertions won't work in this case. > > Back to assertions. I thought we might consider > MPI_Initialized_subset(*flag,required,*provided) or something. > Setting "required" to 0 would return the set of provided assertions > in "provided". Setting "required" to something else will also set > the "flag" to true or false, depending on whether there's a match. > > The special MPI_Init_subset(*argc,***argv,required,*provided) would > complement this. > > Regarding 32 bits, let's count (I'm taking the joint list from the > subset proposal that includes your earlier points): > > 0,1,2,3 - MPI_THREAD_SINGLE, FUNNELED, SERIALIZED, MULTIPLE > 0x00000004 - No dynamic process support > 0x00000008 - No file I/O > 0x00000010 - No one-sided ops > 0x00000020 - No communicator & group management > 0x00000040 - No non-blocking communication > 0x00000080 - No message cancellation > 0x00000100 - Persistent ops on both sides > 0x00000200 - No heterogeneity > 0x00000400 - No derived datatypes (especially those with holes) > 0x00000800 - No MPI_ANY_SOURCE > 0x00001000 - No message tagging > 0x00002000 - No reduction order > 0x00004000 - No eager buffering > 0x00008000 - No mixed request types in wait/test > > We have 16 bits left. Note that there may be some predefined masks > for well defined combinations of the above (e.g., MPI-1 = no dynamic > processes, no file I/O, no threads, etc.). > > Best regards. > > Alexander > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Richard Treumann > Sent: Monday, May 05, 2008 11:53 PM > To: MPI 2.2 > Subject: [Mpi-22] MPI_INIT assertions > I changed the subject to be meaningful - it had been "Re: [Mpi-22] > mpi-22 Digest, Vol 2, Issue 7" > > I do think this proposal is within the scope of the MPI 2.2 rules so > I am pleased to hear this is being considered. > > I am 100% convinced that a query function should be part of this > proposal, probably with 2 query flavors. One flavor of the query > would respond with the set of assertions the application > MPI_INIT_xxx call had provided and another would respond with the > set of assertions the MPI implementation is actually exploiting. > > One library author may decide he will use if/else logic based on how > the MPI implementation will behave. The application may assert > MPI_NO_yyy but if the MPI implementation does not exploit MPI_NO_yyy > then the library can still use the code that depends on yyy. Another > library author may depend unconditionally on yyy. On an MPI > implementation that does not exploit MPI_NO_yyy he may want to issue > a warning that assertion MPI_NO_yyy is non-portable but let the job > run. On one that does exploit MPI_NO_yyy he would abort the job. Or, > he may decide to simply abort any job that asserts MPI_NO_yyy to > avoid having the library suddenly quit working when the customer > upgrades to an MPI implementation that does exploit MPI_NO_yyy. > > I think 32 assertions is probably more than enough > > Even a handful of defined assertions can raise testing costs. For > simple cases like MPI_NO_ANY_SOURCE it is easy for a user to judge > whether a piece of code is OK but if we begin to add subtle or > narrow semantic assertions it gets harder. Some library providers > will be tempted to say "I cannot proof read and test my code to a > degree that will allow me to accept 28 specific assertions and > forbid 4. I will simply forbid every subtle assertion I cannot > afford to test." > > I predict that for large applications developed by teams and for > community open source efforts the design leads will consider > requiring that all parts be written to live within a few carefully > chosen assertions. The design leads will not want to provide a list > of 26 subtle or narrow assertions and require that everyone respect > all 26 in the code they contribute. > > Many distinct assertions also could become a big test cost for MPI > implementors and customers who must qualify an MPI implementation > before trusting their business to it. If there were 64 or more > assertions, how would a tester decide what combinations of > assertions must be tested and then create suitable test cases? > > Dick > > Dick Treumann - MPI Team/TCEM > IBM Systems & Technology Group > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > Tele (845) 433-7846 Fax (845) 433-8363 > > > mpi-22-bounces_at_[hidden] wrote on 05/05/2008 01:28:06 PM: > > > Dear Dick, > > > > Thank you. We can actually introduce what you propose, possibly with > > a query function to make it still easier to live with, as early as > > in MPI 2.2, as a subset precursor. Judging by the discussion in > > Chicago, subsets may not need much more than that in the end, > > possibly with a little more flags and semantics added in MPI-3. > > > > The reservation against 32- (or for that matter, 64-) bit limitation > > is the only one I have at the moment. Not being able to attach > > assertions to communicators, etc. may be missed by some advanced > > programmers, but here we need to be pragmatic: who will ever want to > > go that deep? > > > > Best regards. > > > > Alexander > > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > > bounces_at_[hidden]] On Behalf Of Richard Treumann > > Sent: Monday, May 05, 2008 7:18 PM > > To: MPI 2.2 > > Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > > Hi Alexander > > > > I have no objection to citing my "assertions" proposal in the > > subsetting discussions. I do want to keep it clear that this > > proposal is intended to be as simple as practical to implement, exploit and > > live with. > > > > "Live with" applies to 3rd party library authors or anyone else who > > must write MPI code but does not know and control the structure of > > the entire application. That guy must "live with" the decisions made > > by whoever coded the MPI_INIT piece. "Live with" also applies to > > whoever must test or certify a specific MPI implementation. > > > > Thanks - Dick > > > > Dick Treumann - MPI Team/TCEM > > IBM Systems & Technology Group > > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > > Tele (845) 433-7846 Fax (845) 433-8363 > > > > [image removed] "Supalov, Alexander" <alexander.supalov_at_[hidden]> > > > > > > > "Supalov, Alexander" <alexander.supalov_at_[hidden]> > > Sent by: mpi-22-bounces_at_[hidden] > > 04/26/2008 04:03 AM > > > > Please respond to > > "MPI 2.2" <mpi-22_at_[hidden]> > > > > [image removed] > > To > > > > [image removed] > > "MPI 2.2" <mpi-22_at_[hidden]> > > > > [image removed] > > cc > > > > [image removed] > > > > [image removed] > > Subject > > > > [image removed] > > Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > > > [image removed] > > > > [image removed] > > > > > > Dear Dick, > > > > Thank you. Would you mind if I cite your proposal in the subsets > > discussion? Yours looks like a good alternative to the thinking of > > some of us that subsets might be very rich and mutable, and to > > Jeff's proposal on hints I've already cited there with his permission. > > > > Best regards. > > > > Alexander > > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > > bounces_at_[hidden]] On Behalf Of Richard Treumann > > Sent: Thursday, April 24, 2008 6:16 PM > > To: MPI 2.2 > > Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > Dick Treumann - MPI Team/TCEM > > IBM Systems & Technology Group > > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > > Tele (845) 433-7846 Fax (845) 433-8363 > > > > > > mpi-22-bounces_at_[hidden] wrote on 04/24/2008 11:33:42 AM: > > > > > Hi, > > > > > > Note that this is an argument for making the assertions optional: those > > > who don't care don't have to use them. Those who care should use them > > > correctly or else. As usual. > > > > > > Best regards. > > > > > > Alexander > > > > > > > Hi Alexander > > > > The assertions are optional in this proposal. If this is added to > > the MPI standard the minimal impacts (day one impacts) are: > > > > == > > To application writers (none) - MPI_INIT and MPI_INIT_THREAD still > > work. MPI_INIT_THREAD_xxx can be > > passed 0 (zero) as the assertions bit vector. > > > > To MPI Implementors (small) - subroutine MPI_INIT_THREAD_xxx can be > > a clone of MPI_INIT_THREAD under the covers. If the Forum decides > > the query function is for asking what assertions are being honored, > > the implementation can just return "none" to every query. If there > > is also a query for what assertions have been made then there are a > > few more lines of code the implementor must write to preserve the > > value so it can be returned(maybe 10 lines) > > > > Writers of opaque libraries (small) - call the query function at > > library init time and if any assertions are found, issue an error > > message and kill the job. This is awkward for a library that wants > > to support every MPI whether it has implemented the new query > function or not. > > == > > > > As MPI implementations begin to take advantage of assertions there > > is more work for the MPI implementor and the library author must > > begin to think about whether his customer will be upset if the > > library simply outlaws all assertions. > > > > The library author will never be wrong if he simply forbids > > assertions forever. If they become valuable he will feel the > > pressure to work it out. > > > > The MPI implementor will never be wrong if he adds the API but > > simply ignores assertions forever. If they become valuable he will > > feel the pressure to honor some at least. > > --------------------------------------------------------------------- > > 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. > > _______________________________________________ > > 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. > _______________________________________________ > 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. 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Re: [Mpi-22] MPI_INIT assertions
by unknown＠example.com 08 May '08

08 May '08

Dear Dick, Thank you, I think I start feeling the difference between the assertions and the hints. To be completely sure, where would you put the soft spawning info key: is this an assertion or a hint? What about other standardized info elements that materially influence the program execution or may even predetermine its success or failure (like wdir)? More generally, will the difference between assertions and hints justify the use of two different mechanisms to pass the data across the MPI boundary? Here's I think what we can save by dropping certain MPI features: * Dynamic process support: less overhead in the progress engine, easier global rank handling. * File I/O: smaller requests, easier wait/test functions. * One-sided ops: no passive target w/o MPI calls - no extra progress thread. * Communicator & group management: better memory footprint. * Non-blocking communication: easier ordering, simplified request handling. * Heterogeneity: better memory footprint, easier data handling. * Derived datatypes (especially those with holes): better memory footprint. * Message tagging: better support for stable dataflow exchanges, smaller packets. Best regards. Alexander ________________________________ From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Richard Treumann Sent: Tuesday, May 06, 2008 5:21 PM To: MPI 2.2 Subject: Re: [Mpi-22] MPI_INIT assertions In my view, each assertion we define in the standard should be justified by a good explanation of how it allows an MPI implementation to be more efficient and what cost/risk it adds In effect, a cost/benefit analysis. No plausible rationale - no assertion. An assertion is a statement about the application. It is not a request for libmpi to "provide something". In my proposal, an application that correctly uses some assertion must still be written to work on an MPI implementation that ignores that assertion. An application that incorrectly uses some assertion can fail or give wrong answers. You can picture an assertion as the application author granting libmpi permission to "NOT provide something" at the MPI implementors discretion. In MPI 2 we maintained a careful distinction between hints and assertions. The MPI implementation is not allowed to give wrong results or error messages when an application provides an incorrect hint. If an application could provide a hint that it would not use MPI_CANCEL on a particular communicator and then called MPI_CANCEL, it would be OK for libmpi to use a really slow CANCEL protocol but not OK for it to issue a fatal error or ignore the CANCEL. That means that the freedom to "exploit" a hint in libmpi is very limited and less care is required of the user in providing hints. Much of what is being proposed should be treated as hints and could use a different and extensible mechanism. We can consider extending the MPI_Info usage in MPI-3 to address information passing that is hint-like. The MPI standard intends applications to be platform agnostic and source level portable and we should not break that. An assertions interface for making statements about the application will not limit this kind of portability. If there are no MPI_CANCEL calls today, there are no MPI_CANCEL calls after recompilation for a new platform. If we add features for platform tuning (like how many tasks per node or eager threshhold) we could damage portability. In my first outline, I threw in MPI-IO and MPI-1SC without any rationale for how they are useful. You added: "No communicator & group management", "No non-blocking communication", "No message tagging" and "No derived datatypes". It is not clear to me they are all useful so a decent rationale would be needed for each. That makes 6 bits that may be free. The thread support level parameter in MPI_INIT_THREAD is a request to the MPI library to provide some level of thread support and I question how cleanly that maps into the "assertions" model. The assertions model may only require one bit for "MPI_NO_THREAD_CONTENTION". That frees 3 more of the bits you suggest are already taken. If we conclude that all 4 thread support options are really useful it may be best to add the assertions flag to MPI_INIT_THREAD and keep the thread support controls as they are. Even the MPI_NO_THREAD_CONTENTION bit frees up then. My original thought was that we would add a new function that adds a parameter to MPI_INIT_THREAD. I am convinced that the number of assertions defined by the MPI standard should be very limited because each brings some risk and complicates life for library writers. If we end up with as many as 32 assertions I will apologize for having offered the idea in the first place and probably advocate a no vote. If MPI 2.2 provided only MPI_NO_EAGER_THROTTLE, MPI_NO_SEND_CANCEL, MPI_NO_REQUEST_MIX, MPI_NO_ANY_SOURCE and MPI_NO_REDUCTION_ORDER I would be content and debate about adding more could wait for MPI 3.0. The assertion that the application does not try to match persistent send/recv with nonpersistent recv/send would be a nice 2.2 bonus. That accounts for 6 bits. The query function could be something as simple as: MPI_Query_assertions(int *stated, int *exploited) The author of libfred could code in his Init_fred routine: int stated_by_app, exploited_by_lib; MPI_Query_assertions( &stated_by_app, &exploited_by_lib) if (exploited_by_lib & MPI_NO_SEND_CANCEL) fatal_error("Assertion MPI_NO_SEND_CANCEL is not compatable with Fred Lib") else if (stated_by_app & MPI_NO_SEND_CANCEL) warn("Assertion MPI_NO_SEND_CANCEL is not compatable with Fred Lib. It is not exploited by your MPI but your application will not port to an MPI that does exploit MPI_NO_SEND_CANCEL"); If Fred is really cautious he can code If (stated_by_app != 0) fatal_error("Fred does not like assertions") and see if anybody asks for some assertion to be tolerated in the next release of FredLib. You mention "No eager buffering" which is different than what I proposed and is not logically an "assertion". MPI applications should not depend semantically on eager buffering today and the standard is clear that a MPI implementation which has no eager buffering can still be 100% compliant. The standard requires that IF an MPI implementation provides an eager protocol as a performance enhancement, it must also provide a safety feature which can be expensive. Many (perhaps most) applications can benefit from an eager protocol but do not need the safety feature because the application is self regulating. These applications could assert: "I do not require the safety feature." which would allow them the benefit of eager protocol without the costs of the safety feature. I can see a rationale for some kind of hints related to eager protocol buffer space and threshhold. There are many other kinds of granular "hint" support that may be useful but all that should be kept distinct from this proposal (In my opinion). Regards - Dick Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 mpi-22-bounces_at_[hidden] wrote on 05/06/2008 07:26:03 AM: > Dear Dick, > > Thanks. What about passing more verbose information to and from an > MPI implementation? Say, eager threshold value, if it's meaningful? > There are many less controversial examples, for example, to let the > caller know how many processes are placed onto the node, etc. Simple > assertions won't work in this case. > > Back to assertions. I thought we might consider > MPI_Initialized_subset(*flag,required,*provided) or something. > Setting "required" to 0 would return the set of provided assertions > in "provided". Setting "required" to something else will also set > the "flag" to true or false, depending on whether there's a match. > > The special MPI_Init_subset(*argc,***argv,required,*provided) would > complement this. > > Regarding 32 bits, let's count (I'm taking the joint list from the > subset proposal that includes your earlier points): > > 0,1,2,3 - MPI_THREAD_SINGLE, FUNNELED, SERIALIZED, MULTIPLE > 0x00000004 - No dynamic process support > 0x00000008 - No file I/O > 0x00000010 - No one-sided ops > 0x00000020 - No communicator & group management > 0x00000040 - No non-blocking communication > 0x00000080 - No message cancellation > 0x00000100 - Persistent ops on both sides > 0x00000200 - No heterogeneity > 0x00000400 - No derived datatypes (especially those with holes) > 0x00000800 - No MPI_ANY_SOURCE > 0x00001000 - No message tagging > 0x00002000 - No reduction order > 0x00004000 - No eager buffering > 0x00008000 - No mixed request types in wait/test > > We have 16 bits left. Note that there may be some predefined masks > for well defined combinations of the above (e.g., MPI-1 = no dynamic > processes, no file I/O, no threads, etc.). > > Best regards. > > Alexander > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > bounces_at_[hidden]] On Behalf Of Richard Treumann > Sent: Monday, May 05, 2008 11:53 PM > To: MPI 2.2 > Subject: [Mpi-22] MPI_INIT assertions > I changed the subject to be meaningful - it had been "Re: [Mpi-22] > mpi-22 Digest, Vol 2, Issue 7" > > I do think this proposal is within the scope of the MPI 2.2 rules so > I am pleased to hear this is being considered. > > I am 100% convinced that a query function should be part of this > proposal, probably with 2 query flavors. One flavor of the query > would respond with the set of assertions the application > MPI_INIT_xxx call had provided and another would respond with the > set of assertions the MPI implementation is actually exploiting. > > One library author may decide he will use if/else logic based on how > the MPI implementation will behave. The application may assert > MPI_NO_yyy but if the MPI implementation does not exploit MPI_NO_yyy > then the library can still use the code that depends on yyy. Another > library author may depend unconditionally on yyy. On an MPI > implementation that does not exploit MPI_NO_yyy he may want to issue > a warning that assertion MPI_NO_yyy is non-portable but let the job > run. On one that does exploit MPI_NO_yyy he would abort the job. Or, > he may decide to simply abort any job that asserts MPI_NO_yyy to > avoid having the library suddenly quit working when the customer > upgrades to an MPI implementation that does exploit MPI_NO_yyy. > > I think 32 assertions is probably more than enough > > Even a handful of defined assertions can raise testing costs. For > simple cases like MPI_NO_ANY_SOURCE it is easy for a user to judge > whether a piece of code is OK but if we begin to add subtle or > narrow semantic assertions it gets harder. Some library providers > will be tempted to say "I cannot proof read and test my code to a > degree that will allow me to accept 28 specific assertions and > forbid 4. I will simply forbid every subtle assertion I cannot > afford to test." > > I predict that for large applications developed by teams and for > community open source efforts the design leads will consider > requiring that all parts be written to live within a few carefully > chosen assertions. The design leads will not want to provide a list > of 26 subtle or narrow assertions and require that everyone respect > all 26 in the code they contribute. > > Many distinct assertions also could become a big test cost for MPI > implementors and customers who must qualify an MPI implementation > before trusting their business to it. If there were 64 or more > assertions, how would a tester decide what combinations of > assertions must be tested and then create suitable test cases? > > Dick > > Dick Treumann - MPI Team/TCEM > IBM Systems & Technology Group > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > Tele (845) 433-7846 Fax (845) 433-8363 > > > mpi-22-bounces_at_[hidden] wrote on 05/05/2008 01:28:06 PM: > > > Dear Dick, > > > > Thank you. We can actually introduce what you propose, possibly with > > a query function to make it still easier to live with, as early as > > in MPI 2.2, as a subset precursor. Judging by the discussion in > > Chicago, subsets may not need much more than that in the end, > > possibly with a little more flags and semantics added in MPI-3. > > > > The reservation against 32- (or for that matter, 64-) bit limitation > > is the only one I have at the moment. Not being able to attach > > assertions to communicators, etc. may be missed by some advanced > > programmers, but here we need to be pragmatic: who will ever want to > > go that deep? > > > > Best regards. > > > > Alexander > > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > > bounces_at_[hidden]] On Behalf Of Richard Treumann > > Sent: Monday, May 05, 2008 7:18 PM > > To: MPI 2.2 > > Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > > Hi Alexander > > > > I have no objection to citing my "assertions" proposal in the > > subsetting discussions. I do want to keep it clear that this > > proposal is intended to be as simple as practical to implement, exploit and > > live with. > > > > "Live with" applies to 3rd party library authors or anyone else who > > must write MPI code but does not know and control the structure of > > the entire application. That guy must "live with" the decisions made > > by whoever coded the MPI_INIT piece. "Live with" also applies to > > whoever must test or certify a specific MPI implementation. > > > > Thanks - Dick > > > > Dick Treumann - MPI Team/TCEM > > IBM Systems & Technology Group > > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > > Tele (845) 433-7846 Fax (845) 433-8363 > > > > [image removed] "Supalov, Alexander" <alexander.supalov_at_[hidden]> > > > > > > > "Supalov, Alexander" <alexander.supalov_at_[hidden]> > > Sent by: mpi-22-bounces_at_[hidden] > > 04/26/2008 04:03 AM > > > > Please respond to > > "MPI 2.2" <mpi-22_at_[hidden]> > > > > [image removed] > > To > > > > [image removed] > > "MPI 2.2" <mpi-22_at_[hidden]> > > > > [image removed] > > cc > > > > [image removed] > > > > [image removed] > > Subject > > > > [image removed] > > Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > > > [image removed] > > > > [image removed] > > > > > > Dear Dick, > > > > Thank you. Would you mind if I cite your proposal in the subsets > > discussion? Yours looks like a good alternative to the thinking of > > some of us that subsets might be very rich and mutable, and to > > Jeff's proposal on hints I've already cited there with his permission. > > > > Best regards. > > > > Alexander > > > > From: mpi-22-bounces_at_[hidden] [mailto:mpi-22- > > bounces_at_[hidden]] On Behalf Of Richard Treumann > > Sent: Thursday, April 24, 2008 6:16 PM > > To: MPI 2.2 > > Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7 > > Dick Treumann - MPI Team/TCEM > > IBM Systems & Technology Group > > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 > > Tele (845) 433-7846 Fax (845) 433-8363 > > > > > > mpi-22-bounces_at_[hidden] wrote on 04/24/2008 11:33:42 AM: > > > > > Hi, > > > > > > Note that this is an argument for making the assertions optional: those > > > who don't care don't have to use them. Those who care should use them > > > correctly or else. As usual. > > > > > > Best regards. > > > > > > Alexander > > > > > > > Hi Alexander > > > > The assertions are optional in this proposal. If this is added to > > the MPI standard the minimal impacts (day one impacts) are: > > > > == > > To application writers (none) - MPI_INIT and MPI_INIT_THREAD still > > work. MPI_INIT_THREAD_xxx can be > > passed 0 (zero) as the assertions bit vector. > > > > To MPI Implementors (small) - subroutine MPI_INIT_THREAD_xxx can be > > a clone of MPI_INIT_THREAD under the covers. If the Forum decides > > the query function is for asking what assertions are being honored, > > the implementation can just return "none" to every query. If there > > is also a query for what assertions have been made then there are a > > few more lines of code the implementor must write to preserve the > > value so it can be returned(maybe 10 lines) > > > > Writers of opaque libraries (small) - call the query function at > > library init time and if any assertions are found, issue an error > > message and kill the job. This is awkward for a library that wants > > to support every MPI whether it has implemented the new query > function or not. > > == > > > > As MPI implementations begin to take advantage of assertions there > > is more work for the MPI implementor and the library author must > > begin to think about whether his customer will be upset if the > > library simply outlaws all assertions. > > > > The library author will never be wrong if he simply forbids > > assertions forever. If they become valuable he will feel the > > pressure to work it out. > > > > The MPI implementor will never be wrong if he adds the API but > > simply ignores assertions forever. If they become valuable he will > > feel the pressure to honor some at least. > > --------------------------------------------------------------------- > > 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. > > _______________________________________________ > > 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. > _______________________________________________ > 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. *

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