Re: [Mpi3-rma] RMA proposal 1 update

19 May 2010

      Are you referring to this email?
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you allreduce(MPI_SUM, 1 million element integer vector == 4MB)? Then you know how many things you should have received and when you have received all of those you can enter a barrier?
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If each origin (in a fence epoch) keeps track of the count(s) of RMA>> operations to each of its targets, then an allreduce of those arrays>> will>> tell each target how many operations were done to itself and can be>> used to>> determine completion.
please help undestand this better, where does allreduce (in MPI terms) came into the picture here? There is no big vector. I want to do get_1, add_1, get_2, add_2, get_3, add_3 when there is not support for collective reduce in the network. Can this be worse than complete_1, complete_2, complete_3
Vinod.
From: [email protected]
To: [email protected]
Date: Wed, 19 May 2010 13:38:43 -0600
Subject: Re: [Mpi3-rma] RMA proposal 1 update

Yes, it can be worse.  See later emails in the thread…

Keith

From:
[email protected]
[mailto:[email protected]] On Behalf Of Vinod
tipparaju

Sent: Wednesday, May 19, 2010 1:34 PM

To: MPI 3.0 Remote Memory Access working group

Subject: Re: [Mpi3-rma] RMA proposal 1 update

I
am very much for supporting collective remote completion. Many optimizations
are possible here.
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The question then turns to the
"other networks". If you can't figure out remote completion, then the
collective is going to be pretty heavy, right?
May
be this will help make the point. When there is a network that does support a
collective remote completion semantic (say, using its collective network reduce
operation), would this functionality not help get better performance on that
network? Would this functionality, for n collective completions,  ever be
worse than completion_1+completion_2+completion_3+...completion_n? If not, why
not have it?
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From: [email protected]
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To: [email protected]
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Date: Sun, 16 May 2010 20:32:36 -0600
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Subject: Re: [Mpi3-rma] RMA proposal 1 update
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Before doing that, can someone sketch out the platform/API and the
implementation that makes that more efficient? There is no gain for Portals (3
or 4). There is no gain for anything that supports Cray SHMEM reasonably well
(shmem_quiet() is approximately the same semantics as MPI_flush_all). Hrm, you
can probably say the same thing about anything that supports UPC well - a
strict access is basically a MPI_flush_all(); MPI_Put(); MPI_flush_all();...
Also, I thought somebody said that IB gave you a notification of remote
completion...
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The question then turns to the "other networks". If you can't
figure out remote completion, then the collective is going to be pretty heavy,
right?
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Keith
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-----Original Message-----
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From: [email protected] [mailto:mpi3-rma-
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[email protected]] On Behalf Of Jeff Hammond
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Sent: Sunday, May 16, 2010 7:27 PM
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To: MPI 3.0 Remote Memory Access working group
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Subject: Re: [Mpi3-rma] RMA proposal 1 update
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Tortsten,
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There seemed to be decent agreement on adding MPI_Win_all_flush_all
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(equivalent to MPI_Win_flush_all called from every rank in the
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communicator associated with the window) since this function can be
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implemented far more efficiently as a collective than the equivalent
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point-wise function calls.
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Is there a problem with adding this to your proposal?
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Jeff
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On Sun, May 16, 2010 at 12:48 AM, Torsten Hoefler
<[email protected]>
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wrote:
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Hello all,
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After the discussions at the last Forum I updated the group's
first
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proposal.
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The proposal (one-side-2.pdf) is attached to the wiki page
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https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/RmaWikiPage
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The changes with regards to the last version are:
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1) added MPI_NOOP to MPI_Get_accumulate and MPI_Accumulate_get
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2) (re)added MPI_Win_flush and MPI_Win_flush_all to passive
target
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mode
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Some remarks:
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1) We didn't straw-vote on MPI_Accumulate_get, so this function
might
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go. The removal would be very clean.
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2) Should we allow MPI_NOOP in MPI_Accumulate (this does not
make
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sense
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and is incorrect in my current proposal)
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3) Should we allow MPI_REPLACE in
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MPI_Get_accumulate/MPI_Accumulate_get?
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(this would make sense and is allowed in the current
proposal but
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we
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didn't talk about it in the group)
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All the Best,
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Torsten
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--
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bash$ :(){ :|:&};: ---------------------
http://www.unixer.de/ -----
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Torsten Hoefler         | Research Associate
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Blue Waters Directorate | University of Illinois
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1205 W Clark Street     | Urbana, IL, 61801
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NCSA Building           | +01 (217)
244-7736
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_______________________________________________
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--
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Jeff Hammond
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Argonne Leadership Computing Facility
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[email protected] / (630) 252-5381
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http://www.linkedin.com/in/jeffhammond
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Vinod tipparaju

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