On Thu, 2007-07-19 at 18:00 +0200, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <[email protected]> wrote:
>
> > > /*
> > > - * Monotonic_clock - returns # of nanoseconds passed since time_init()
> > > + * Scheduler clock - returns current time in nanosec units.
> > > + * Now based on virtual cpu time to only account time the guest
> > > + * was actually running.
> >
> > Runn*ing*? Does it include time the VCPU spends idle/blocked? If
> > not, then the scheduler won't be able to tell how long a process has
> > been asleep. Maybe this doesn't matter (I had this problem in a
> > version of Xen's sched_clock, and I can't say I saw an ill effects
> > from it).
No, it does not include idle time, if we're going idle the cpu timer
gets stopped.
> CFS does measure time elapsed across task-sleep periods (and does
> something similar to what the old scheduler's 'sleep average'
> interactivity mechanism did), but that mechanism measures "time spent
> running during sleep", not "time spent idling".
>
> still, CFS needs time measurement across idle periods as well, for
> another purpose: to be able to do precise task statistics for /proc.
> (for top, ps, etc.) So it's still true that sched_clock() should include
> idle periods too.
I'm not sure, s390 already has an implemetation for precise accounting
in the architecture code, does CFS also improve accounting data?
Jan
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