linux-kernel - Re: [PATCH V4 3/3] perf tool: Add sort key symoff for perf diff

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Date:	Thu, 20 Nov 2014 15:18:44 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	kan.liang@...el.com, jolsa@...hat.com,
	linux-kernel@...r.kernel.org, ak@...ux.intel.com
Subject: Re: [PATCH V4 3/3] perf tool: Add sort key symoff for perf diff

On Tue, 18 Nov 2014 18:13:19 -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Nov 18, 2014 at 11:38:20AM -0500, kan.liang@...el.com escreveu:
>> From: Kan Liang <kan.liang@...el.com>
>> 
>> Sometime, especially debugging scaling issue, the function level diff
>> may be high granularity. The user may want to do deeper diff analysis
>> for some cache or lock issue. The "symoff" key can let the user sort
>> differential profile by ips. This feature should only work when the
>> perf.data comes from same binary.
>
> So, to avoid having people scratching heads, and since we have the
> build-id for both perf.data files, hence for both binaries being
> compared, can we check the build ids and either refuse to do the diff or
> print a big warning about different binaries being compared?

Why do you think so?  I think it's fine to use symoff for different
binaries for same reason as the symbol sort key.  Even if some functions
were changed, other DSOs and/or functions still have same offset and
thus have meaningful diff result IMHO.

Thanks,
Namhyung
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