linux-kernel - Re: [PATCH 3/3] perf, tools: Add support for guest/host-only profiling

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Date:	Tue, 10 May 2011 18:09:46 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
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 3/3] perf, tools: Add support for guest/host-only
 profiling

On Tue, 2011-05-10 at 17:46 +0200, Roedel, Joerg wrote:
> 
> I intended to re-use the exlude_hv bit originally, but then I looked
> into how this bit is used. On PPC it looks like this bit is set when
> Linux itself runs as a guest to exclude the hypervisor code being
> profiled. The meaning here is different (beacause Linux itself is the
> hypervisor) and I wanted to avoid different semantics for this bit
> across architectures. So I introduces seperate bits.
> The exclude_hv bit can be used when we have some kind of perf-ctr
> support for KVM guests. 

Ah, I didn't mean it like that, yes HV is strictly something different
(and you understood its purpose well, its when the 'host' is a guest
itself). What I was wondering about is if we want HV to be included in
the Guest/Host exclusion mask or not.

Then again, I guess that'll change behaviour in non-obvious ways, so
better not do that.

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