linux-kernel - Re: [PATCH -tip] perf, x86: P4 PMU - Add missing read of a counter before test

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Date:	Thu, 24 Mar 2011 21:03:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Don Zickus <dzickus@...hat.com>, Lin Ming <ming.m.lin@...el.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] perf, x86: P4 PMU - Add missing read of a counter
 before test


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> On 03/24/2011 09:22 PM, Don Zickus wrote:
> > On Thu, Mar 24, 2011 at 07:46:40PM +0300, Cyrill Gorcunov wrote:
> >>>> The read of a proper MSR register was missed so instead of a counter the 
> >>>> configration register is tested (it has ARCH_P4_UNFLAGGED_BIT always cleared) 
> >>>> and unflagged overflows never have been catched. Fix it by reading a proper 
> >>>> MSR register.
> >>>
> >>> So what effect does this have on the regular perf user? Please try to describe 
> >>> the real-life effect of the bug/problem fixed here.
> >>>
> >>> Thanks,
> >>>
> >>> 	Ingo
> >>
> >> Unflagged overflows never have been catched due to missed read of a register which
> >> is to signalize about it, and as result unknown nmi may happen leading to
> >> "Dazen and confused" message. That is what supposed to be in changelog?
> > 
> > I think Ingo is looking for something like this:
> > 
> 
> Thanks Don, if Ingo agree I can update it.

Sure - please resend the final patch in a clean thread, with a proper title, 
etc.

Thanks,

	Ingo
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