Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] OpenMPI job initializing problem
From: Beichuan Yan (beichuan.yan_at_[hidden])
Date: 2014-03-20 22:59:03

Here is an example of my data measured in seconds:

communication overhead = commuT + migraT + print,
compuT is computational cost,
totalT = compuT + communication overhead,
overhead% denotes percentage of communication overhead

intelmpi (walltime=00:03:51)
iter [commuT migraT printT] compuT totalT overhead%
3999 4.945993e-03 2.689362e-04 1.440048e-04 1.689100e-02 2.224994e-02 2.343795e+01
5999 4.938126e-03 1.451969e-04 2.689362e-04 1.663089e-02 2.198315e-02 2.312373e+01
7999 4.904985e-03 1.490116e-04 1.451969e-04 1.678491e-02 2.198410e-02 2.298933e+01
9999 4.915953e-03 1.380444e-04 1.490116e-04 1.687193e-02 2.207494e-02 2.289473e+01

openmpi (walltime=00:04:32)
iter [commuT migraT printT] compuT totalT overhead%
3999 3.574133e-03 1.139641e-04 1.089573e-04 1.598001e-02 1.977706e-02 1.864836e+01
5999 3.574848e-03 1.189709e-04 1.139641e-04 1.599526e-02 1.980305e-02 1.865278e+01
7999 3.571033e-03 1.168251e-04 1.189709e-04 1.601100e-02 1.981783e-02 1.860879e+01
9999 3.587008e-03 1.258850e-04 1.168251e-04 1.596618e-02 1.979589e-02 1.875587e+01

It can be seen that Open MPI is faster in both communication and computation measured by MPI_Wtime calls, but the wall time reported by PBS pro is larger.


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

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
For corporate legal information go to:
users mailing list
users mailing list