Heavy I/O blocks FreeBSD box for several seconds

Steve Kargl sgk at troutmask.apl.washington.edu
Wed Jul 6 17:01:33 UTC 2011

On Wed, Jul 06, 2011 at 06:38:23PM +0200, Hartmann, O. wrote:
> On 07/06/11 18:28, Steve Kargl wrote:
> >On Wed, Jul 06, 2011 at 05:29:24PM +0200, O. Hartmann wrote:
> >>I use SCHED_ULE on all machines, since it is supposed to be performing
> >>better on multicore boxes, but there are lots of suggestions switching
> >>back to the old SCHED_4BSD scheduler.
> >>
> >If you are using MPI in numerical codes, then you want
> >to use SCHED_4BSD.  I've posted numerous times about ULE
> >and its very poor performance when using MPI.
> >
> >http://lists.freebsd.org/pipermail/freebsd-hackers/2008-October/026375.html
> >
> Worth a try,
> but most of my code I use is OpenMP, not MPI.

It may impact OpenMP.  I don't have any OpenMP to test.  But,
if OpenMP is spawning as many or more threads than the number
of available processors/cores, then I think you will have 

> The post is of 2008, that's three years ago and 9.0 is on the brink to 
> become released ...

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.


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