An application that is really trying to do overlap of communication and computation is likely to post Isends and Irecvs before entering a computation step. If the computation step discovers the answer and another iteration is not needed then why require all the sends and receives to be done? The application already knows the data is useless. A master/worker application may have an outstanding MPI_Irecv at each worker with tag 1 to pick up workload and an outstanding MPI_Irecv with tag 2 that is looking for the "all done" message. When the "all done" shows up, the workload MPI_Irecv needs to be completed before a disconnect can proceed. Why make the master send a null workload to each worker just to clear those obsolete MPI_Irecvs? The standard has several points at which it states that all outstanding sends and receives must be complete. If an Isend or Irecv has been posted there are 2 ways to complete it: Make the matching Send or Recv happen or call MPI_Cancel. The pair of operations MPI_Cancel; MPI_Wait will always complete no matter what the other side does. As long as the application does not care whether the data is delivered, this is a clean way to satisfy the requirement that all outstanding sends and receives must be complete. I have not been following the FT stuff but it seems like MPI_Cancel would be useful there. If I have posted an MPI_Irecv from task 9 and then learned task 9 is gone why wouldn't I want the option of doing an MPI_Cancel on the MPI_Irecv request? That seems cleaner than any other way of getting rid of the receive descriptor. 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 From: "Supalov, Alexander" <[email protected]> To: "MPI 3.0 Fault Tolerance and Dynamic Process Control working Group" <[email protected]> Date: 01/13/2010 03:52 PM Subject: Re: [Mpi3-ft] Nonblocking Process Creation and Management Sent by: [email protected] Thanks. Do we know any active app that uses the JOIN still? If none, why the heck keep it afloat? I meant CANCEL in all its varieties. Again, how many apps cannot live without it? From: [email protected] [ mailto:[email protected]] On Behalf Of Richard Treumann Sent: Wednesday, January 13, 2010 9:48 PM To: MPI 3.0 Fault Tolerance and Dynamic Process Control working Group Subject: Re: [Mpi3-ft] Nonblocking Process Creation and Management Why would JOIN be any less useful today than in the past? Why would you want to deprecate it? It is a trivial bootstrap for the simplest form of ACCEPT/CONNECT. It just hides the ACCEPT and CONNECT operations and lets the user handle the complexity of identifying the two end points any way he likes. I never felt JOIN was needed very badly but it went in as a "what the heck" decision and I do not see that anything has changed. Is it because IJOIN seems more difficult than IACCEPT and ICONNECT in some way? When you say CANCEL should be deprecated, do you mean MPI_Cancel of an outstanding ISEND/IRECV request or something else? 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 Inactive hide details for "Supalov, Alexander" ---01/13/2010 02:53:18 PM---Thanks. I meant the JOIN per se as a way of establis"Supalov, Alexander" ---01/13/2010 02:53:18 PM---Thanks. I meant the JOIN per se as a way of establishing the communicator. Do we need that still? Wh From: "Supalov, Alexander" <[email protected]> To: "MPI 3.0 Fault Tolerance and Dynamic Process Control working Group" <[email protected]> Date: 01/13/2010 02:53 PM Subject: Re: [Mpi3-ft] Nonblocking Process Creation and Management Sent by: [email protected] Thanks. I meant the JOIN per se as a way of establishing the communicator. Do we need that still? What practically relevant cases can be provided to justify its continuing existence? If there are none, we should rather deprecate the JOIN and drop the IJOIN. Good point on the CANCEL. -----Original Message----- From: [email protected] [ mailto:[email protected]] On Behalf Of Josh Hursey Sent: Wednesday, January 13, 2010 8:25 PM To: MPI 3.0 Fault Tolerance and Dynamic Process Control working Group Subject: Re: [Mpi3-ft] Nonblocking Process Creation and Management Since join() does a handshake to create the new communicator, it should be delayed by the remote side of the protocol. A nonblocking version would allow the application to possibly do other computation while waiting for the remote side. As far as Cancel, I have been thinking that it might be useful for Accept and Connect. Though with the normal problems of Cancel, I don't know how to really specify it. I want to look into it a bit more before next week to see if anything useful can be said of using Cancel with Accept/Connect. -- Josh On Jan 13, 2010, at 2:01 PM, Supalov, Alexander wrote:

Hi,

Do we really need the IJOIN thing? I think the JOIN itself should be deprecated. Just as CANCEL, by the way.

Best regards.

Alexander

-----Original Message----- From: [email protected] [ mailto:[email protected] ] On Behalf Of Josh Hursey Sent: Tuesday, January 12, 2010 11:04 PM To: MPI 3.0 Fault Tolerance and Dynamic Process Control working Group Subject: [Mpi3-ft] Nonblocking Process Creation and Management

I extended and cleaned up the Nonblocking Process Creation and Management proposal on the wiki: https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/Async-proc-mgmt

I added the rest of the nonblocking interface proposals, and touched up some of the language. I do not have an implementation yet, but will work on that next. There are a few items that I need to refine a bit still (e.g., MPI_Cancel, mixing of blocking and nonblocking), but this should give us a foundation to start from.

I would like to talk about this next week during our working group slot at the MPI Forum meeting.

Let me know what you think, and if you see any problems.

Thanks, Josh

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