linux-kernel - Re: [PATCH] perf: ARM: Record the user-mode PC in the call chain.

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Message-ID: <20130620090728.GA2842@mudshark.cambridge.arm.com>
Date:	Thu, 20 Jun 2013 10:07:29 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jed Davis <jld@...illa.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: ARM: Record the user-mode PC in the call chain.

On Thu, Jun 20, 2013 at 04:17:06AM +0100, Jed Davis wrote:
> On Tue, Jun 18, 2013 at 02:13:19PM +0100, Will Deacon wrote:
> > On Fri, Jun 14, 2013 at 12:21:11AM +0100, Jed Davis wrote:
> > > With this change, we no longer lose the innermost entry in the user-mode
> > > part of the call chain.  See also the x86 port, which includes the ip.
> > > 
> > > It's possible to partially work around this problem by post-processing
> > > the data to use the PERF_SAMPLE_IP value, but this works only if the CPU
> > > wasn't in the kernel when the sample was taken.
> > 
> > Thanks. I guess we need something similar for arm64 too. Could you cook a
> > similar patch please?
> 
> Done (and tested, on the ARM V8 Foundation Model).

Wow, I didn't expect you to test it. Thanks!

> It looked as if the powerpc and sparc ports might have similar issues,
> but I haven't checked on them yet.

I can extract some hardware from the pile in the corner of my flat if you
want a hand with testing.

Will
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