On Tue, 2007-08-21 at 10:42 +0200, Ingo Molnar wrote: > * Christian Borntraeger <[EMAIL PROTECTED]> 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.
scheduler_tick() is based on the HZ timer which uses the TOD clock = real time. sched_clock() currently uses the TOD clock as well so in regard to the new scheduler we currently do not have a problem. We have a problem with cpu time accounting, the change to the /proc code breaks the precise accounting on s390. To solve the cpu time accounting we need to change sched_clock() to the cpu timer = virtual time. To change the scheduler_tick() as well requires another patch and I fear it would complicate things in the s390 backend. And if you say that the scheduling becomes invariant to steal-time, how is the cpu time accounting via sum_exec supposed to work if it does not take steal-time into account ? -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
