[mpich-discuss] MPICH2 1.3 speed down on Windows 2008 R2

[Youri LACAN-BARTLEY]

Hi Jayesh,

First of all, thank you for the swift reply.

To answer your question, I've been basically binding my mpi jobs with "-binding user:0,1,2,3,[...],29,30,31" since I'm using all available cores on the machine. It's this specific scenario that is bugging me.
I have tried running jobs with let's say 8 cores and specifying different bindings (per core, per socket, shared L2 cache, etc) and the results were what I was expecting.
What I can't explain is why I obtain such a massive speed down between running on 16 cores and 32 cores.
I might be overlooking something but I really can't put my finger on it.

I've even played around with channels (sock, nemesis, etc) in the hope that this might shed some light on the issue but to no avail.

If you need more detailed information, don't hesitate to ask.

Thanks for the help,

Youri LACAN-BARTLEY

-----Message d'origine-----
De : Jayesh Krishna [mailto:jayesh at mcs.anl.gov] 
Envoyé : mercredi 27 avril 2011 17:30
À : mpich-discuss at mcs.anl.gov
Cc : Youri LACAN-BARTLEY
Objet : Re: [mpich-discuss] MPICH2 1.3 speed down on Windows 2008 R2

Hi,
 What is the binding used ? Did you try different bindings to see if that changes the performance (Does not specifying user defined binding increase/decrease perf)?
 More details please.

-Jayesh

----- Original Message -----
From: "Youri LACAN-BARTLEY" <youri.lacan-bartley at transvalor.com>
To: mpich-discuss at mcs.anl.gov
Sent: Wednesday, April 27, 2011 4:04:25 AM
Subject: [mpich-discuss] MPICH2 1.3 speed down on Windows 2008 R2





Hi, 



I’m currently benchmarking a 32 core machine with four Intel X7560 running Windows 2008 R2. 

I’ve noticed severe speed down when running on all 32 cores at once using user defined binding and the nemesis channel. 

Would anyone have any idea why this might be the case. 

I’ve run the exact same hardware with the same software running CentOS 5 and OpenMPI 1.4 and in that case the results show a regular speed up as expected. 



Am I hitting a specific MPICH2 issue or has this rather got something to do with Windows? 



Kind regards, 



Youri LACAN-BARTLEY 


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