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July 2014

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Ticket 435 and Re: MPI_Win_allocate_shared and synchronization functions
by Rolf Rabenseifner 02 Jul '14

02 Jul '14

Bill, Rajeev, and all other RMA WG members, Hubert and Torsten discussed already in 2012 the meaning of the MPI one-sided synchronization routines for MPI-3.0 shared memory. This question is still unresolved in the MPI-3.0 + errata. Does the term "RMA Operation" include "a remote load/store from an origin process to the window Memory on a target"? Or not? The ticket #435 expects "not". In this case, MPI_Win_fence and post-start-complete-wait cannot be used for synchronizing the sending process of data with the receiving process of data that use only local and remote load/stores on shared memory windows. Ticket 435 extends the meaning of MPI_Win_fence and post-start-complete-wait that they provide sender-Receiver synchronization between processes that use local and remote load/stores on shared memory windows. I hope that all RMA working group members, agree that - currently the behavior of these sync-routines for shared memory remote load/stores is undefined due to the undefined definition of "RMA Operation" - and that we need an errata that resolves this problem. What is your opinion about the solution provided in https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/435 ? Best regards Rolf PS: Ticket 435 is the result of a discussion of Pavan, Hubert and I at ISC2014. ----- Original Message ----- > From: Hubert Ritzdorf > Sent: Tuesday, September 11, 2012 7:26 PM > To: mpi3-rma(a)lists.mpi-forum.org > Subject: MPI_Win_allocate_shared and synchronization functions > > Hi, > > it's quite unclear what Page 410, Lines 17-19 > > A consistent view can be created in the uni?fied > memory model (see Section 11.4) by utilizing the window > synchronization functions (see > Section 11.5) > > really means. Section 11.5 doesn't mention any (load/store) access to > shared memory. > Thus, must > > (*) RMA communication calls and RMA operations > be interpreted as RMA communication calls (MPI_GET, MPI_PUT, > ...) and > ANY load/store access to shared > window > (*) put call as put call and any store to shared memory > (*) get call as get call and any load from shared memory > (*) accumulate call as accumulate call and any load or store access > to shared window ? > > Example: Assertion MPI_MODE_NOPRECEDE > > Does > > the fence does not complete any sequence of locally issued RMA calls > > mean for windows created by MPI_Win_Allocate_shared () > > the fence does not complete any sequence of locally issued RMA calls > or > any load/store access to the window memory ? > > It's not clear to me. I will be probably not clear for the standard > MPI user. > RMA operations are defined only MPI functions for window objects > (as far as I can see). > But possibly I'm totally wrong and the synchronization functions > synchronize > only the RMA communication calls (MPI_GET, MPI_PUT, ...). > > Hubert > > ----------------------------------------------------------------------------- > > Wednesday, September 12, 2012 11:37 AM > > Hubert, > > This is what I was referring to. I'm in favor of this proposal. > > Torsten > -- Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner(a)hlrs.de High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)

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