Heavy I/O blocks FreeBSD box for several seconds
sgk at troutmask.apl.washington.edu
Wed Jul 6 18:00:02 UTC 2011
On Wed, Jul 06, 2011 at 05:05:41PM +0000, Poul-Henning Kamp wrote:
> In message <20110706170132.GA68775 at 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.
> To find out: Run gstat and keep and eye on the leftmost column
> The road map for fixing that has been known for years...
I'll keep this in mind, the next time I upgrade the cluster.
It's currently running a Feb 10th vintage kernel, and is
under fairly heavy use at the moment.
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