On Thu, 2013-08-08 at 23:02 +0800, ethan.zhao wrote:
> 在 2013-8-6，下午3:29，Mike Galbraith <bitbuc...@online.de> 写道：
>
> > +int sched_needs_cpu(int cpu)
> > +{
> > + return cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost;
> > +}
> > +
> > #else /* CONFIG_NO_HZ_COMMON */
> >
> > static inline bool got_nohz_idle_kick(void)
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -548,7 +548,7 @@ static ktime_t tick_nohz_stop_sched_tick
> > time_delta = timekeeping_max_deferment();
> > } while (read_seqretry(&jiffies_lock, seq));
> >
> > - if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> > + if (sched_needs_cpu(cpu) || rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> > arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
> > next_jiffies = last_jiffies + 1;
> > delta_jiffies = 1;
>
> If the performace regression was caused by too much expensive clock device
> reprogramming and too frequent entering /exiting of C-states… this patch
> should work.
> except the following result is almost always false under 3.11-rc3 code.
>
> > return cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost;
On my E5620 box, avg_idle works fine. Patchlet doesn't save as much as
it used to, thanks to Peter's patch now killing the worst of the pain,
but it does still does save cycles. I have too much regression left to
say exactly what it can now save max, doesn't matter much either.
The pertinent numbers:
v3.11-rc4-27-ge4ef108 496.7 KHz .858 1.030 throttle+peterz
v3.11-rc4-27-ge4ef108 440.7 KHz .761 1.296 nothrottle+peterz
-Mike
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
