Messages in this thread Patch in this message | | | Date | Thu, 19 Apr 2012 14:51:29 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] clocksource, prevent overflow in clocksource_cyc2ns |
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On Thu, 19 Apr 2012, Thomas Gleixner wrote:
> On Wed, 18 Apr 2012, Prarit Bhargava wrote: > > There's also some additional information that I've been gathering on this issue; > > I have seen *idle* systems switch to the hpet because the clocksource watchdog > > hits the overflow comparison. As expected it happens much less frequently on > > newer kernels (linux.git top of tree) than older stable kernels (2.6.32 based) > > due to the difference in shift values but it is happening in both cases. > > > > The odd thing about this behaviour is that I would expect it to occur with the > > same frequency on small systems as it does on large systems with linux.git as > > the watchdog fires once/second. AFAICT I do not see this on small systems but > > see it only on systems with greater than 24 cpus (both Intel and AMD). > > > > Using debug code similar to the dump code I previously provided, I can see that > > every so often these large systems can hit a case where the tsc wraps and the > > hpet is still monotonically increasing. When the unstable calculation is > > performed the result is obviously affected by the overflow. Sometimes this > > comparison overflow happens within 18 minutes, other times it can take hours or > > days. > > You are describing symptoms, but the root cause is obviously that the > watchdog does not get invoked in time. The question is why. > > Can you please add the patch below and enable scheduler, timer and irq > events in the tracer. Tracing will stop once the watchdog triggers. > > Please provide the traces. We need to understand the root cause of > this idle wreckage. > > Thanks, > > tglx
-ENOPATCH :)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index c958338..2214323 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -287,11 +287,15 @@ static void clocksource_watchdog(unsigned long data) cs->cs_last = csnow; cs->wd_last = wdnow; + trace_printk("wd %lld %lld cs %lld %lld\n" , wdnow, wd_nsec, + csnow, cs_nsec); + if (atomic_read(&watchdog_reset_pending)) continue; /* Check the deviation from the watchdog clocksource. */ if ((abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD)) { + tracing_off(); clocksource_unstable(cs, cs_nsec - wd_nsec); continue; }
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