[Mpi3-rma] FW: draft of a proposal for RMA interfaces

[Vinod tipparaju]

Jeff, Are you going to be attending the forum this week? I will try to address some of the alternatives you mention below in the presentation tomorrow.Thanks,Vinod.> Date: Tue, 9 Dec 2008 13:15:59 -0600> From: jeff.science at gmail.com> To: mpi3-rma at lists.mpi-forum.org> Subject: Re: [Mpi3-rma] FW: draft of a proposal for RMA interfaces> > On Tue, Dec 9, 2008 at 7:51 AM, Vinod tipparaju <tipparajuv at hotmail.com> wrote:> >>> inside of GA, I have to manually do everything that ARMCI_Malloc did previously?>>>> yes the user has to. Do you think that is a bad idea?> > I think it depends on the user.  I see the following possibilities:> > 1. MPI RMA includes functionality for allocating different types of> memory segments (shared, private, etc.) just as ARMCI did, and perhaps> more functionality than that.  MPI knows when users are abusing memory> and can address this directly via useful error messages, etc.> > 2. A separate library which makes managing the complexities of on-node> memory in a heterogeneous and/or multicore context is developed> independently of MPI.> > 3. Users roll there own in all cases...>     a. ...resulting in properly executing code which runs at top speed> because the user knows what they are doing or their usage is simple> enough that it doesn't matter.>     b. ...correctly but with limited performance because a naive> approach is used.>     c. ...leading to catastrophic problems because they don't know> what they're doing.> > I know of enough evil hacking among application programmers to greatly> fear (3c).  The negative consequences of (3b) depend on the machine.> For example, if one uses  basic malloc and all memory is> process-private, then on a big SMP node like Ranger at TACC, the> performance will suffer because the RMA will not completely bypass the> communication protocol, as GA/ARMCI currently does.  Even when MPI RMA> shortcuts when it knows it is staying within a node, there still must> be a memcpy between the two segments of private memory that would not> occur if the user uses shmalloc.  Of course, some users may want this> for consistency but for others it may kill performance.> > I don't believe I understand all the issues clearly enough to say much> more, but if MPI aims to support heterogeneous platforms, the> complexity of on-node memory hierarchies that paradigm introduces,> along with the complexity of dealing with different types of multicore> CPUs, suggests that MPI users would benefit greatly from an allocator> which encapsulates these various paradigms into a single, portable> framework which is in sync with MPI's RMA protocol.> > I imagine a mix of (2) and (3) is the most likely scenario but (2)> won't fully address the problem unless it focuses directly on being> paired with MPI RMA.  As a user, and a stupid and lazy one at that,> (1) is the best I can hope for.> > Thanks,> > Jeff> > -- > Jeff Hammond> The University of Chicago> http://home.uchicago.edu/~jhammond/> _______________________________________________> mpi3-rma mailing list> mpi3-rma at lists.mpi-forum.org> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
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