SCHED_ULE should not be the default
sgk at troutmask.apl.washington.edu
Fri Dec 23 00:59:33 UTC 2011
On Thu, Dec 22, 2011 at 04:23:29PM -0800, Adrian Chadd wrote:
> On 22 December 2011 11:47, Steve Kargl <sgk at troutmask.apl.washington.edu> wrote:
> > There is the additional observation in one of my 2008
> > emails (URLs have been posted) that if you have N+1
> > cpu-bound jobs with, say, job0 and job1 ping-ponging
> > on cpu0 (due to ULE's cpu-affinity feature) and if I
> > kill job2 running on cpu1, then neither job0 nor job1
> > will migrate to cpu1. ?So, one now has N cpu-bound
> > jobs running on N-1 cpus.
> .. and this sounds like a pretty serious regression. Have you ever
> filed a PR for it?
No. I was interacting directly with jeffr in 2008. I got
as far as setting up root access on a node for jeffr.
Unfortunately, both jeffr and I got busy with real life,
and 4BSD allowed me to get my work done.
> > Finally, my initial post in this email thread was to
> > tell O. Hartman to quit beating his head against
> > a wall with ULE (in an HPC environment). ?Switch to
> > 4BSD. ?This was based on my 2008 observations and
> > I've now wasted 2 days gather additional information
> > which only re-affirms my recommendation.
> I personally don't think this is time wasted. You've done something
> that noone else has actually done - provided actual results from
> real-life testing, rather than a hundred posts of "I remember seeing
> X, so I don't use ULE."
> If you can definitely and consistently reproduce that N-1 cpu bound
> job bug, you're now in a great position to easily test and re-report
> KTR/schedtrace results to see what impact they have. Please don't
> underestimate exactly how valuable this is.
I'll try this tomorrow. I first need to modify the code I used
in the 2008 test to disable IO, so that it is nearly completely
> How often are those two jobs migrating between CPUs? How am I supposed
> to read "CPU load" ? Why isn't it just sitting at 100% the whole time?
This is my 1st foray into ktr and schedgraph, so I may not have done
something incorrectly. In particular, it seems that schedgraph takes
the cpu clock as a command line argument, so there is probably
some scaling that I'm missing.
> Would you mind repeating this with 4BSD (the N+1 jobs) so we can see
> how the jobs are scheduled/interleaved? Something tells me we'll see
> it the jobs being scheduled evenly
Sure, I'll do this tomorrow as well.
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