linux-kernel - Re: [PATCH 00/12] perf_events: add support for sampling taken branches (v2)

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Date:	Tue, 06 Dec 2011 12:03:32 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"acme@...hat.com" <acme@...hat.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"robert.richter@....com" <robert.richter@....com>,
	"ravitillo@....gov" <ravitillo@....gov>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>
Subject: Re: [PATCH 00/12] perf_events: add support for sampling taken
 branches (v2)

On Tue, 2011-12-06 at 09:49 +0000, Will Deacon wrote:
> On Mon, Dec 05, 2011 at 10:39:26PM +0000, Peter Zijlstra wrote:
> > On Fri, 2011-10-14 at 14:37 +0200, Stephane Eranian wrote:
> > > This patchset adds an important and useful new feature to
> > > perf_events: branch stack sampling. In other words, the
> > > ability to capture taken branches into each sample.
> > > 
> > Other than the few comments given it all looks good. My main worry is
> > the Intel only aspect, I'd really love for there to be another platform
> > that could implement at least part of this.
> 
> I discussed this with Stephane in Prague and, although it would be lovely to
> have this on ARM, we simply don't have the hardware to do it. So the nature
> of series does seem to be x86-centric unless there's way to do a watered
> down version in software.

The only way to do this in software would be like
CONFIG_PROFILE_ALL_BRANCHES and that's horrid (and kernel only).

But there's more than Intel & ARM, but it looks like PPC doesn't have
this either and I suspect MIPS and SPARC don't either, which doesn't
leave us with much else.

So I guess we should just go ahead and merge this and hope more hardware
grows this feature in a compatible enough manner.
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