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Subject: Re: [OMPI users] knem/openmpi performance?
From: Paul Kapinos (kapinos_at_[hidden])
Date: 2013-07-15 03:43:18

On 07/12/13 12:55, Jeff Squyres (jsquyres) wrote:
> FWIW: a long time ago (read: many Open MPI / knem versions ago),
> I did a few benchmarks with knem vs. no knem Open MPI installations.
> IIRC, I used the typical suspects like NetPIPE, the NPBs, etc.
> There was a modest performance improvement (I don't remember the numbers offhand);
> it was a smaller improvement than I had hoped for
> -- particularly in point-to-point message passing latency (e.g., via NetPIPE).

Jeff, I would turn the question the other way around:

- are there any penalties when using KNEM?

We have a couple of Really Big Nodes (128 cores) with non-huge memory bandwidth
(because coupled of 4x standalone nodes with 4 sockets each). So cutting the
bandwidth in halves on these nodes sound like Very Good Thing.

But otherwise we've 1500+ nodes with 2 sockets and 24GB memory only and we do
not wanna to disturb the production on these nodes.... (and different MPI
versions for different nodes are doofy).



Dipl.-Inform. Paul Kapinos   -   High Performance Computing,
RWTH Aachen University, Center for Computing and Communication
Seffenter Weg 23,  D 52074  Aachen (Germany)
Tel: +49 241/80-24915