perf_event: when events are grouped, the time enabled / running values are incorrect
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From: Peter Zijlstra on 11 May 2010 16:20 On Tue, 2010-05-11 at 21:55 +0200, stephane eranian wrote: > Events are also grouped in this example. Both this same issue exists > also when only > one event is used. I suspect an update_event_times() or > update_group_times() is also > missing on the sampling path in perf_overflow_handler(). Hrmm, you're right, except fixing that is non-trivial. update_event_times() wants to be called with ctx->lock held and we can't do that from NMI context. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 11 May 2010 16:30
On Tue, 2010-05-11 at 22:23 +0200, Stephane Eranian wrote: > On Tue, May 11, 2010 at 10:11 PM, Peter Zijlstra <peterz(a)infradead.org> wrote: > > On Tue, 2010-05-11 at 21:55 +0200, stephane eranian wrote: > >> Events are also grouped in this example. Both this same issue exists > >> also when only > >> one event is used. I suspect an update_event_times() or > >> update_group_times() is also > >> missing on the sampling path in perf_overflow_handler(). > > > > Hrmm, you're right, except fixing that is non-trivial. > > update_event_times() wants to be called with ctx->lock held and we can't > > do that from NMI context. > > > Why do you need the lock when the event is running on a CPU in NMI context? > What action issued remotely could modify the data used by this function without > the need for IPI? Not sure, would at the very least have to verify that. I'll try and have a look. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |