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    SubjectRe: [patch] sched: accurate user accounting
    On Mon, 26 Mar 2007, Con Kolivas wrote:

    > On Sunday 25 March 2007 23:06, malc wrote:
    >> On Sun, 25 Mar 2007, Con Kolivas wrote:
    >>> On Sunday 25 March 2007 21:46, Con Kolivas wrote:
    >>>> On Sunday 25 March 2007 21:34, malc wrote:
    >>>>> On Sun, 25 Mar 2007, Ingo Molnar wrote:
    >>>>>> * Con Kolivas <kernel@kolivas.org> wrote:
    >>>>>>> For an rsdl 0.33 patched kernel. Comments? Overhead worth it?
    >>
    >> [..snip..]
    >>
    >>> ---
    >>> Currently we only do cpu accounting to userspace based on what is
    >>> actually happening precisely on each tick. The accuracy of that
    >>> accounting gets progressively worse the lower HZ is. As we already keep
    >>> accounting of nanosecond resolution we can accurately track user cpu,
    >>> nice cpu and idle cpu if we move the accounting to update_cpu_clock with
    >>> a nanosecond cpu_usage_stat entry. This increases overhead slightly but
    >>> avoids the problem of tick aliasing errors making accounting unreliable.
    >>>
    >>> Signed-off-by: Con Kolivas <kernel@kolivas.org>
    >>> Signed-off-by: Ingo Molnar <mingo@elte.hu>
    >>
    >> [..snip..]
    >>
    >> Forgot to mention. Given that this goes into the kernel, shouldn't
    >> Documentation/cpu-load.txt be amended/removed?
    >
    > Yes that's a good idea. Also there should be a sanity check because sometimes
    > for some reason noone's been able to explain to me sched_clock gives a value
    > which doesn't make sense (time appears to have gone backwards) and that will
    > completely ruin the accounting from then on.

    After running this new kernel for a while i guess i have hit this issue:
    http://www.boblycat.org/~malc/apc/bad-load.png

    Top and icewm's monitor do show incredibly huge load while in reality
    nothing like that is really happening. Both ad-hoc and `/proc/stat' (idle)
    show normal CPU utilization (7% since i'm doing some A/V stuff in the
    background)

    --
    vale
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