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Subject: Re: [OMPI users] [Fwd: mpi alltoall memory requirement]
From: Ashley Pittman (ashley_at_[hidden])
Date: 2009-05-13 07:48:45

On Thu, 2009-04-23 at 07:12 +0000, viral.vkm_at_[hidden] wrote:
> Hi
> Thanks for your response.
> However, I am running
> mpiexec .... -ppn 24 -n 192 /opt/IMB-MPI1 alltaoll -msglen /root/temp
> And file /root/temp contains entry upto 65535 size only. That means
> alltoall test will run upto 65K size only
> So, in that case I will require very less memory but then in that case
> also test is running out-of-memory. Please help someone to understand
> the scenario.
> Or do I need to switch to some algorithm or do I need to set some
> other environment variables ? or anything like that ?

I'm not sure but I seem to remember that IMB uses two application
buffers and alternates which one it uses, this itself will double the
memory requirement. You should be able to plot performance against max
message size and see where the drop off occurs.

I've always used the compile options to specify max message size and rep
count, the -msglen option is not one I've seen before.

Ashley Pittman.