linux-kernel - Re: [PATCH 1/3] perf, core: Introduce attrs to count in either host or guest mode

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Date:	Tue, 10 May 2011 16:59:02 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 1/3] perf, core: Introduce attrs to count in either host
 or guest mode

On Tue, May 10, 2011 at 10:45:46AM -0400, Peter Zijlstra wrote:
> On Tue, 2011-05-10 at 16:35 +0200, Joerg Roedel wrote:
> > +       /* Can't exclude counting in guest and in host mode */
> > +       if (attr.exclude_host && attr.exclude_guest)
> > +               return -EINVAL;
> 
> Why not?

By definition the counter won't count at all. The hardware just ignores
the bits if they are both set. My rationale here was that it does not
makes sense to setup a counter and exclude guest and host mode.

	Joerg


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