linux-kernel - Re: [Bug] ARM 'perf' regression by commit a43cb95d5

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Message-ID: <20130517095423.GD23112@mudshark.cambridge.arm.com>
Date:	Fri, 17 May 2013 10:54:23 +0100
From:	Will Deacon <will.deacon@....com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Bug] ARM 'perf' regression by commit a43cb95d5

On Fri, May 17, 2013 at 10:48:23AM +0100, Ming Lei wrote:
> On Fri, May 17, 2013 at 5:36 PM, Will Deacon <will.deacon@....com> wrote:
> >
> > It's probably easier if you choose a workload, otherwise it's difficult to
> > see what is `correct' and what is broken. For example, your broken output
> > seems to be in the smsc95xx driver, so assumedly there's a bunch of
> > networking going on whereas your other output is in cpuidle_enter_state.
> 
> If all modules are removed, the result will become OK. And if I only insert one
> module, the top sample will fall inside the only module, but I am sure
> nothing is working on the symbols of the module.

Can you check your dmesg please? I suppose the smsc95xx driver might be
screaming about something and somehow the changes to the reg printing have
made it get stuck.

> >
> > We need an apples-for-apples comparison if you think there's a bug in the
> > kernel. Can you try profiling hackbench or something?
> >
> >> Or could anyone else try to verify the problem on their own environment?
> >
> > How are you running perf top?
> 
> sudo perf top

... and did hackbench make any difference (i.e. is the profile more stable)?

Will
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