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Date: Wed, 15 Sep 2010 19:28:05 +0200
From: Robert Richter <robert.richter@amd.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
CC: Stephane Eranian <eranian@google.com>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>, Don Zickus <dzickus@redhat.com>,
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        "andi@firstfloor.org" <andi@firstfloor.org>
Subject: Re: [PATCH] perf, x86: catch spurious interrupts after disabling
 counters
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On 15.09.10 13:02:22, Cyrill Gorcunov wrote:
> > what's for sure, is that you can have an interrupt in flight by the time
> > you disable.
> > 
> 
> I fear you can x86_pmu_stop()
> 
> 	if (__test_and_clear_bit(hwc->idx, cpuc->active_mask)) {
> 
> --->		active_mask will be cleared here for sure
> --->		but counter still ticks, say nmi happens active_mask
> --->		is cleared, but NMI can still happen and gets buffered
> --->		before you disable counter in real
> 
> 		x86_pmu.disable(event);
> 		cpuc->events[hwc->idx] = NULL;
> 		WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);
> 		hwc->state |= PERF_HES_STOPPED;
> 	}
> 
> No?

I tried reordering this too, but it didn't fix it.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center