Re: [accounting regression since rc1] scheduler updates

Balbir Singh
2007-08-20T19:00:30Z

Martin Schwidefsky wrote:
> On Mon, 2007-08-20 at 20:08 +0200, Ingo Molnar wrote:
>> For sched_clock()'s behavior while the virtual CPU is idle: my current
>> idea for that is the patch below (a loosely analoguous problem exists
>> with nohz/dynticks): it makes sched_clock() valid across idle periods
>> too and uses wall-clock time for that.
>
> Ok, that would mean that sched_clock can just return the virtual cpu
> time and the two hooks starts and stops the idle periods as far as the
> scheduler is concerned. In this case we can use the patch from Jan with
> the new implementation for sched_clock and add the two hooks to the
> places where the cpu-idle notifiers are done (do_monitor_call and
> default_idle). In fact this could be an idle-notifier. Hmm, I take a
> closer look tomorrow when I'm back at the office.
>

<snip>

I am partially responsible for the regression. While working on the
CPU accounting change, I for some unknown reason always assumed
that sched_clock() was virtualized. I should have taken a closer look.

Ingo, with this new approach, sched_clock() although not virtualized,
advances as if it is (due to the idle state change accounting).
I have one question though, what if the underlying CPU is forcefully
scheduled out from the virtual CPU?

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL