Re: [accounting regression since rc1] scheduler updates

Ingo Molnar
2007-08-21T08:43:17Z

* Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> Am Montag, 20. August 2007 schrieb Ingo Molnar:
> > could you send that precise sched_clock() patch? It should be an order
> > of magnitude simpler than the high-precision stime/utime tracking you
> > already do, and it's needed for quality scheduling anyway.
>
> I have a question about that. I just played with sched_clock, and even
> when I intentionally slow down sched_clock by a factor of 2, my cpu
> bound process gets 100 % in top. If this is intentional, I dont
> understand how a virtualized sched_clock would fix the accounting
> change?

hm, does on s390 scheduler_tick() get driven in virtual time or in real
time? The very latest scheduler code will enforce a minimum rate of
sched_clock() across two scheduler_tick() calls (in rc3 and later
kernels). If sched_clock() "slows down" but scheduler_tick() still has a
real-time frequency then that impacts the quality of scheduling. So
scheduler_tick() and sched_clock() must really have the same behavior
(either both are virtual or both are real), so that scheduling becomes
invariant to steal-time.

Ingo