Re: [patch] sched: accurate user accounting

From: Ingo Molnar
Date: Thu Jun 14 2007 - 16:43:20 EST

* Vassili Karpov <av1474@xxxxxxxx> wrote:

> Hello Ingo and others,
> After reading and noticing few
> refernces to accounting i decided to give CFS a try. With
> sched-cfs-v2.6.21.4-16 i get pretty weird results, it seems like
> scheduler is dead set on trying to move the processes to different
> CPUs/cores all the time. And with hog (manually tweaking the amount
> iterations) i get fairly strange resuls, first of all the process is
> split between two cores, secondly while integral load provided by the
> kernel looks correct, it's off by good 20 percent on each idividial
> core.
> (
> Thought this information might be of some interest.

hm - what does 'hog' do, can i download hog.c from somewhere?

the alternating balancing might be due to an uneven number of tasks
perhaps? If you have 3 tasks on 2 cores then there's no other solution
to achieve even performance of each task but to rotate them amongst the

> P.S. How come the /proc/stat information is much closer to reality
> now? Something like what Con Kolivas suggested was added to
> sched.c?

well, precise/finegrained accounting patches have been available for
years, the thing with CFS is that there we get them 'for free', because
CFS needs those metrics for its own logic. That's why this information
is much closer to reality now. But note: right now what is affected by
the changes in the CFS patches is /proc/PID/stat (i.e. the per-task
information that 'top' and 'ps' displays, _not_ /proc/stat) - but more
accurate /proc/stat could certainly come later on too.

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