Re: [patch] sched: accurate user accounting

[Con Kolivas <kernel@kolivas.org>]

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. 

-- 
-ck