linux-kernel - Re: [PATCH 1/1] perf tools: perf diff for different binaries

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Date:	Wed, 05 Nov 2014 15:32:34 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	"Liang\, Kan" <kan.liang@...el.com>
Cc:	"acme\@kernel.org" <acme@...nel.org>,
	"jolsa\@kernel.org" <jolsa@...nel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"andi\@firstfloor.org" <andi@...stfloor.org>
Subject: Re: [PATCH 1/1] perf tools: perf diff for different binaries

Hi Kan,

On Tue, 4 Nov 2014 17:07:43 +0000, Kan Liang wrote:
> Hi Namhyung,
>
>> >                             tchain_edit        [.] f1
>> >      0.14%        3.913444  tchain_edit        [.] f2
>> >     99.82%        1.005478  tchain_edit        [.] f3
>> 
>> Hmm.. I think it should be a default behavior for perf diff, otherwise -s
>> symbol is almost meaningless IMHO. 
>
> I think we need both instruction level and function level diff.
> For debugging scaling issue, I think we need to do deeper analysis for some
> cache or lock issue. The function level is too high granularity.  
>
> The new option can be used to debug scaling regression issue.
> If the binary/kernel is updated, it doesn't make sense to compare the
> symbol address, since it should be changed. So comparing the function
> should be more useful.
>
>
>> What about setting the
>> sort_sym.se_collapse in data_process() so that hists__match() can use
>> symbol names?
>
> Yes, we can set it if we only do function level diff. But I'd like to keep
> both. So I defined two sort keys.
> "symbol" means "symbol address executed at the time of sample "
> "symbol_name" means "name of function executed at the time of sample"

Hmm.. I don't think the symbol sort key provides the instruction level
diff that you want.  If it finds a symbol it just use the start address
of the symbol, not the exact address of the sample.  Am I missing
something?

Thanks,
Namhyung
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