linux-kernel - Re: [PATCHSET 00/21] perf tools: Add support to accumulate hist periods (v9)

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Message-ID: <533A6C2B.8070801@fb.com>
Date:	Tue, 1 Apr 2014 13:05:07 +0530
From:	Arun Sharma <asharma@...com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rodrigo Campos <rodrigo@...g.com.ar>
Subject: Re: [PATCHSET 00/21] perf tools: Add support to accumulate hist periods
 (v9)

On 4/1/14, 12:58 PM, Namhyung Kim wrote:

>>
>> gdb attributes 0x10370 to a different/known symbol.
>>
>> (gdb) x /i 0x10370
>>     0x10370 <get_cie_encoding+160>:      cmp    $0x4c,%dl
>>
>> Is this known? Could this possibly be caused by stale histogram entries from
>> unmapped/remapped shared libs?
>
> Possibly.
>
> Anyway the addr which perf reported is a mapped address so that it's
> pointless to use the addr directly - it's 7f1b0c963370 in fact.
>

Right - that's the address I'd use if the process in question is still 
running. But gdb <dso name> followed by relative addresses could still 
tell us what the right symbol was?

> What was the exact command line though - did you use any filter
> (--comms, --dsos, --symbols) or event modifiers?  Those are another
> possible culprits since map searching code touched by recent changes.

There were no other filters. The command used was just "perf top".

>
> I'm not able to reproduce the problem on my machine.  It'd be great if
> you could bisect or let me know how to reproduce it easily.
>

I don't have a solid repro either. Involves building a binary, running 
"perf top" and waiting for a few mins until that warning popup appears.

Will try to git bisect and figure out potential culprits.

  -Arun
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