linux-kernel - Re: [PATCH] perf tools: Fix JIT profiling on heap

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Message-ID: <87sisn6ojf.fsf@sejong.aot.lge.com>
Date:	Fri, 17 Jan 2014 16:44:04 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Gaurav Jain <gjain@...com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] perf tools: Fix JIT profiling on heap

Hi Gaurav,

On Thu, 16 Jan 2014 20:23:27 +0000, Gaurav Jain wrote:
> On 1/16/14, 9:37 AM, "Arnaldo Carvalho de Melo" <acme@...stprotocols.net>
> wrote:
>
>>Em Thu, Jan 16, 2014 at 10:49:31AM +0900, Namhyung Kim escreveu:
>>> Gaurav reported that perf cannot profile JIT program if it executes
>>> the code on heap.  This was because current map__new() only handle JIT
>>> on anon mappings - extends it to handle no_dso (heap, stack) case too.
>>> 
>>> This patch assumes JIT profiling only provides dynamic function
>>> symbols so check the mapping type to distinguish the case.  It'd
>>> provide no symbols for data mapping - if we need to support symbols on
>>> data mappings later it should be changed.
>>
>>But we do support symbols in data mappings, that is why we have
>>MAP__VARIABLE, etc, can you elaborate?
>
> Does perf support data mappings from perf map files? Could you please
> share an example of how I may be able to use this.

IIUC there's no difference between function and data mapping.  So you
can use same perf map file for both - in fact there's no way to use
different map file in a single task.  I guess perf will use it to find
only function symbols in function mappings and variables in data
mapping based on the address it accesses.

What I wasn't sure is whether JIT program also produces some dynamic data.
And I think only perf mem command cares about data mappings, no?

Thanks,
Namhyung
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