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    SubjectRe: [patch] sched: accurate user accounting
    On Thu, 14 Jun 2007, Ingo Molnar wrote:

    >
    > * Vassili Karpov <av1474@comtv.ru> wrote:
    >
    >> Hello Ingo and others,
    >>
    >> After reading http://lwn.net/Articles/236485/ 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.
    >>
    >> (http://www.boblycat.org/~malc/apc/hog-cfs-v16.png)
    >>
    >> Thought this information might be of some interest.
    >
    > hm - what does 'hog' do, can i download hog.c from somewhere?

    http://www.boblycat.org/~malc/apc/hog.c and also a in
    Documentation/cpu-load.txt.

    >
    > 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
    > cores.

    One task, one thread. I have also tried to watch fairly demanding video
    (Elephants Dream in 1920x1080/MPEG4) with mplayer, and CFS moves the
    only task between cores almost every second.

    >> 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.

    Aha. I see, it's just that integral load for hog is vastly improved
    compared to vanilla 2.6.21 (then again some other tests are off by a few
    percent (at least), though they were fine with Con's patch (which was
    announced at the beginning of this thread))

    --
    vale
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