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* Andi Kleen <andi@firstfloor.org> wrote:
> Venki Pallipadi <venkatesh.pallipadi@intel.com> writes:
> > > > +void tick_nohz_stop_idle(int cpu)> > +{> > + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
> > +> > + if (ts->idle_active) {> > + ktime_t now, delta;> > + now = ktime_get();
>
> That could be PM timer read costing thousands of cycles.
>
> For going into idle it's probably not a real problem, but it could
> seriously affect out of idle latencies.
at least the current out-of-idle code already does what amounts to a
PM-timer read when exiting from C2 or C3 mode. The
sched_clock_idle_sleep_event() and sched_clock_idle_wakeup_event()
callbacks utilize this already existing time information.
> You would really need a cheaper per CPU timer that doesn't stop in
> idle (which rules out sched_clock). It's all unfortunately quite
> messy.
yep.
Ingo
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