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

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Message-ID: <CACVXFVPEBXat3bPPuHzV535=xLoRMFd03Kjzp=NUF5E3KCq2=g@mail.gmail.com>
Date:	Fri, 17 May 2013 17:27:05 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Will Deacon <will.deacon@....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 4:55 PM, Will Deacon <will.deacon@....com> wrote:
>
> So it's still the morning and I haven't had my coffee yet, but I'm really
> struggling to see what you're getting at. Why does this have anything to do
> with perf?

I don't know, and I just report it out, :-)

I found the problem days ago, and until yesterday I had one more hours to
git-bisect it, but the result is very frustrated.

>
>> [1], 'perf top' mistaken output
>> Samples: 17K of event 'cpu-clock', Event count (approx.): 3516532661
>>  97.51%  [smsc95xx]            [k] 0x013645b8
>>   0.21%  libc-2.15.so          [.] strstr
>>   0.14%  libc-2.15.so          [.] strchr
>>   0.12%  libc-2.15.so          [.] strcmp
>
> [...]
>
>> [2], 'perf top' correct output
>> Samples: 46K of event 'cpu-clock', Event count (approx.): 937128704
>>  96.44%  [kernel]            [k] cpuidle_enter_state
>>   0.19%  libc-2.15.so        [.] strstr
>>   0.16%  [kernel]            [k] kallsyms_expand_symbol.clone.0
>>   0.13%  [kernel]            [k] _raw_spin_unlock_irq
>
> [...]
>
> Are you saying that the profile you're seeing is radically different,
> rather than there being some formatting error that I can't spot? If so, that

Yes.

> sounds really strange and I can't see how the patch you mention is to
> blame...
>
> If we want to persue this, I guess other obvious questions are: which kernel
> are you running? Does this affect multiple architectures (your diff only

Either 3.10-rc1 or today's -next tree(3.10.0-rc1-next-20130516).

> changes ARM)? What's the workload which you are profiling?

I only tested it on Pandaboard, and no real workload, so you can see
cpuidle_enter_state is the top frequent symbol.

Or could anyone else try to verify the problem on their own environment?

Thanks,
--
Ming Lei
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