linux-kernel - Re: [GIT PULL] perf changes for v3.8

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Date:	Sat, 22 Dec 2012 12:30:35 -0700
From:	David Ahern <dsahern@...il.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] perf changes for v3.8

On 12/17/12 3:20 AM, Gleb Natapov wrote:
> Does the regression happen because of commit 20b279ddb38c. If it does I
> think it is safe to revert it. KVM disables PEBS during guest entry now, so
> VMs shouldn't be blowing up (they do not in my testing) and if they still
> do we can disable the counter that has PEBS enabled on a guest entry too.
> Yes, if user runs "perf record -e cycles:ppG" he will not know that
> kernel ignored :pp modifier (with 20b279ddb38c he will get an error), but
> at least old binaries will continue working and new binaries can do the
> checking in userspace.
>

Your patch alone was not enough. Start here:
  https://lkml.org/lkml/2012/7/12/3

And from your response:
https://lkml.org/lkml/2012/7/12/337

"Do not run perf kvm. It does not set exclude_guest and :p and :pp is 
not compatible with guest profiling and should be disallowed. Again 
Peter's patch takes care of this."

20b279ddb38c is Peter's patch -- kernel side enforcement that 
exclude_guest needs to be set when using precise mode.

David
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