On Thu, Apr 18, 2013 at 1:42 PM, Peter Zijlstra <a.p.zijls...@chello.nl> wrote: > On Tue, 2013-04-16 at 06:57 +0000, Pan, Zhenjie wrote: >> Watchdog use performance monitor of cpu clock cycle to generate NMI to >> detect hard lockup. >> But when cpu's frequency changes, the event period will also change. >> It's not as expected as the configration. >> For example, set the NMI event handler period is 10 seconds when the cpu is >> 2.0GHz. >> If the cpu changes to 800MHz, the period will be 10*(2000/800)=25 seconds. >> So it may make hard lockup detect not work if the watchdog timeout is not >> long enough. >> Now, set a notifier to listen to the cpu frequency change. >> And dynamic re-config the NMI event to make the event period correct. >> > > > Urgh,. does this really matter.. all we really want is for that NMI to > hit eventually in the not too distant future. Does the frequency really > matter _that_ much? > I agree, it does not really matter. Set the watchdog to a couple of minutes and it should be fine, shouldn't it?
> Also, can't we simply pick an event that's invariant to the cpufreq > nonsense? Something like CPU_CLK_UNHALTED.REF -- or better the > fixed_ctr2 which nobody ever uses anyway. > You don't want to use fixed counter 2 for NMI watchdog because it's pinned. No other counter can count this event. And it is very useful. I use it often. -- 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/
