On 07/06/11 13:00, Steve Kargl wrote:
On Wed, Jul 06, 2011 at 05:05:41PM +0000, Poul-Henning Kamp wrote:
In message<20110706170132.ga68...@troutmask.apl.washington.edu>, Steve Kargl w

I periodically ran the same type test in the 2008 post over the
last three years.  Nothing has changed.  I even set up an account
on one node in my cluster for jeffr to use.  He was too busy to
investigate at that time.

Isn't this just the lemming-syncer hurling every dirty block over
the cliff at the same time ?

I don't know the answer.  Of course, having no experience in
processing scheduling, I don't understand the question either ;-)

AFAICT, it is a cpu affinity issue.  If I launch n+1 MPI images
on a system with n cpus/cores, then 2 (and sometimes 3) images
are stuck on a cpu and those 2 (or 3) images ping-pong on that
cpu.  I recall trying to use renice(8) to force some load
balancing, but vaguely remember that it did not help.

I've seen exactly this problem with multi-threaded math libraries, as well. Using parallel GotoBLAS on FreeBSD gives terrible performance because the threads keep migrating between CPUs, causing frequent cache misses.
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