linux-kernel - Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters

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Message-ID: <20100915172805.GR13563@erda.amd.com>
Date:	Wed, 15 Sep 2010 19:28:05 +0200
From:	Robert Richter <robert.richter@....com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Stephane Eranian <eranian@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Don Zickus <dzickus@...hat.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: Re: [PATCH] perf, x86: catch spurious interrupts after disabling
 counters

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

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