To me this does not look like a deadlock, proc o will make progress in the wait, and just like with point-to-point commuications process 1 will make general mpi progress while in the bcast. This includes progress on the ibcast so that process 0 can comete it's ibcast and move on to the bcast. Rich ----- Original Message ----- From: [email protected] <[email protected]> To: MPI-3 Collective Subgroup Discussions <[email protected]> Sent: Fri Oct 17 05:14:04 2008 Subject: Re: [mpi3-coll] Non-blocking Collectives Proposal Draft Dear Torsten, Thanks. I'm still unsure I understand how the example would work if processes blocked in the Wait calls as you said below. In this case process 0 would have no chance to reach the Bcast, while process 1 would be inside it and never reached the Wait. Here again is the original diagram: Process 0 Process 1 MPI_Ibarrier(req) MPI_Ibarrier(req) MPI_Wait(req)* MPI Bcast MPI_Bcast* MPI_Wait(req) The stars mark the point where the respective processes would block, as far as I understand. Looks like deadlock? Apart from this, stating that the nonblocking collectives can block in Wait presumes a certain implementation. What if Ibarrier was able to do all right away, and Wait were just a no-op? I think mixing blocking and nonblocking collectives in the proposed way should either be very carefully considered, or simply disallowed. Best regards. Alexander -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Torsten Hoefler Sent: Thursday, October 16, 2008 11:15 PM To: MPI-3 Collective Subgroup Discussions Subject: Re: [mpi3-coll] Non-blocking Collectives Proposal Draft Hello Alexander,
Thank you. The pt2pt progress comment below was taken into account when you removed the nonblocking collective progress description. ah, ok - so I think a reference to the chapter should be sufficient.
As for the example, if it is legal, we should probably count the blocking operations as well when we decide how many simultaneous ops are to be supported. yes, maybe. I am not sure but this could be an issue. It's on the agenda https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/forum201008
Why "if" above: I'm not sure what a delayed nonblocking barrier would mean for process 1. Won't one process possibly block somewhere? Can you explain this please? the barriers will only block in the respective MPI_Wait() (or a tight MPI_Test() loop). But the operation can be initiated as soon as the critical region is left (and there mihgt be some other independent computation to do).
The format matter is complicated. I think it is worth discussing at the Forum as we're likely to have more and more proposals approaching the final stage, when editing them in PDF format will become an issue. yes, it's on the WG agenda - maybe we should discuss this in the whole forum?
Best, Torsten -- bash$ :(){ :|:&};: --------------------- http://www.unixer.de/ ----- Torsten Hoefler | Postdoctoral Researcher Open Systems Lab | Indiana University 150 S. Woodlawn Ave. | Bloomington, IN, 474045, USA Lindley Hall Room 135 | +01 (812) 855-3608 _______________________________________________ mpi3-coll mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-coll --------------------------------------------------------------------- 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. _______________________________________________ mpi3-coll mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-coll