* Andi Kleen <[email protected]> wrote:
> Venki Pallipadi <[email protected]> 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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