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Subject: [OMPI users] switch and NIC performance (was: very bad parallel scaling of vasp using openmpi)
From: Dave Love (d.love_at_[hidden])
Date: 2009-09-23 10:15:45


Rahul Nabar <rpnabar_at_[hidden]> writes:

> So, how does one go about selecting a good switch? "The most expensive
> the better" is somewhat a unsatisfying option!

Also it's apparently not always right, if I recall correctly, according
to the figures on MPI switch performance in the reports somewhere
under http://www.cse.dl.ac.uk/disco.¹ The benchmark database there may
also be relevant. I think they include OMPI figures, to bring this
vaguely on topic.

If you're concerned about latency -- which you may be for VASP? -- then
the NICs and their settings are more important than the switch.
(Obviously use Open-MX, not TCP, too.) See
<http://www.nw-grid.ac.uk/LivMPI> for figures on the NICs I could test.
I haven't seen better GigE ping-pong results than those, but would be
interested to.

---
¹ Not whatever the currently-politically-correct URL is, but it still
  works (except if you turn off Javascript, sigh).