* 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 - 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/