linux-kernel - Re: [PATCH 08/11] perf tool: precise mode requires exclude

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Date:	Tue, 24 Jul 2012 18:15:07 +0200
From:	Robert Richter <robert.richter@....com>
To:	David Ahern <dsahern@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest

David,

On 24.07.12 08:20:19, David Ahern wrote:
> On 7/23/12 12:13 PM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Jul 20, 2012 at 05:25:53PM -0600, David Ahern escreveu:
> >> PEBS cannot be used with guest mode. If user adds :p modifier set
> >> exclude_guest as well.
> >
> > Is this something Intel specific? Or can someone think of an arch where
> > this limitation wouldn't exist?
> 
> Good point. So far precise_ip is used by arch/x86 only. I don't have an 
> AMD based server so I don't know if there is a conflict between 
> virtualization and IBS. Added Robert for advice.

thanks for this hint.

On AMD cpus precise_ip maps to IBS, which does not support hardware
options as perfctrs do. Thus, following attr flags are not supported:

 exclude_user, exclude_kernel, exclude_host, exclude_guest

Counting in guest mode is possible with IBS, but not the exclusion of
a certain mode. If precise_ip counting is enabled on AMD we may not
set the exclude_guest flag.

-Robert

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

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