linux-kernel - Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running perfctrs

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Date:	Fri, 27 Aug 2010 21:33:49 +0200
From:	Robert Richter <robert.richter@....com>
To:	Don Zickus <dzickus@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running
 perfctrs

On 27.08.10 14:57:44, Don Zickus wrote:
> From: Don Zickus <dzickus@...hat.com>
> Date: Fri, 27 Aug 2010 14:43:03 -0400
> Subject: [PATCH] [x86] perf: fix accidentally ack'ing a second event on intel perf counter
> 
> During testing of a patch to stop having the perf subsytem swallow nmis,
> it was uncovered that Nehalem boxes were randomly getting unknown nmis
> when using the perf tool.
> 
> Moving the ack'ing of the PMI closer to when we get the status allows
> the hardware to properly re-set the PMU bit signaling another PMI was
> triggered during the processing of the first PMI.  This allows the new
> logic for dealing with the shortcomings of multiple PMIs to handle the
> extra NMI by 'eat'ing it later.
> 
> Now one can wonder why are we getting a second PMI when we disable all
> the PMUs in the begining of the NMI handler to prevent such a case, for
> that I do not know.  But I know the fix below helps deal with this quirk.
> 
> Tested on multiple Nehalems where the problem was occuring.  With the
> patch, the code now loops a second time to handle the second PMI (whereas
> before it was not).
> 
> Signed-off-by: Don Zickus <dzickus@...hat.com>

Looks good to me. Thanks Don.

-Robert

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

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