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Subject: Re: [OMPI users] OpenMPI job initializing problem
From: Beichuan Yan (beichuan.yan_at_[hidden])
Date: 2014-03-20 17:14:55

As for the performance, my 4-node (64-processes) 3-hour job indicates Intel MPI and OpenMPI have close benchmarks. Intel MPI takes 2:53 while Open MPI takes 3:10.

It is interesting that all my MPI_Wtime calls show OpenMPI is faster (up to twice or even more) than Intel MPI in communication for a single loop, but in overall wall time Open MPI is 10% slower for like 500K loops. The computing times are nearly the same. This is a little confusing.

I may set up and run a new test.


-----Original Message-----
From: users [mailto:users-bounces_at_[hidden]] On Behalf Of Jeff Squyres (jsquyres)
Sent: Thursday, March 20, 2014 11:15
To: Open MPI Users
Subject: Re: [OMPI users] OpenMPI job initializing problem

On Mar 20, 2014, at 12:48 PM, Beichuan Yan <beichuan.yan_at_[hidden]> wrote:

> 2.
> In the upcoming OMPI v1.7, we revamped the shared memory setup code such that it'll actually use /dev/shm properly, or use some other mechanism other than a mmap file backed in a real filesystem. So the issue goes away.

Woo hoo!

> my comment: up to OMPI v1.7.4, this shmem issue is still there. However, it is resolved in OMPI v1.7.5rc5. This is surprising.
> Anyway, OMPI v1.7.5rc5 works well for multi-processes-on-one-node (shmem) mode on Spirit. There is no need to tune TCP or IB parameters to use it. My code just runs well:


> My test data takes 20 minutes to run with OMPI v1.7.4, but needs less than 1 minute with OMPI v1.7.5rc5. I don't know what the magic is. I am wondering when OMPI v1.7.5 final will be released.

Wow -- that sounds like a fundamental difference there. Could be something to do with the NFS tmp directory...? I could see how that could cause oodles of unnecessary network traffic.

1.7.5 should be released ...immanently...

Jeff Squyres
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