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

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Message-ID: <1343248546.26034.68.camel@twins>
Date:	Wed, 25 Jul 2012 22:35:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <robert.richter@....com>
Cc:	David Ahern <dsahern@...il.com>,
	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>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest

On Tue, 2012-07-24 at 18:15 +0200, Robert Richter wrote:
> 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.

IIRC we have SVM enter/exit hooks in kvm/perf already, we could use
those to implement exclude_guest for IBS.

Now I've been trying to find the patches that introduced that, but I'm
failing horridly. Gleb, got us a pointer here?
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