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

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Date:	Thu, 26 Jul 2012 08:50:11 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Robert Richter <robert.richter@....com>,
	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>
Subject: Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest

On Wed, Jul 25, 2012 at 10:35:46PM +0200, Peter Zijlstra wrote:
> 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?
The commit is 144d31e6, but it introduces hook that is used on VMX only.
SVM does not need it to implement guest/host only counters since it
has HW support for that in the PMU.
 
--
			Gleb.
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