Messages in this thread | | | Date | Fri, 13 Feb 2009 10:39:24 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] clockevents: avoid unnecessary reprograming of event timer |
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On Fri, 13 Feb 2009, Ingo Molnar wrote: > > + if (ktime_equal(dev->next_event, expires)) > > + return 0; > > + > > Hm, given that a good high-res source has nanoseconds resolution, > what's the chance of this optimization triggering in practice? > Near zero i think - unless we trigger useless reprogramming without > having added or removed any new timers - but then we should > concentrate on analyzing the reason for that redundant reprogramming. > > Does it trigger often for you?
The only point where this should trigger is when we come out of C2/C3 and switch the local APIC timer back on. There we reload the next_event which was discarded in the hardware before we entered C2/C3 and switched to the broadcast timer. So this change would prevent the rearming of the local APIC after coming out of C2/C3 and probably give us some new C-State related headaches.
Thanks,
tglx
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