linux-kernel - Re: [PATCH v2 3/4] perf-report: add --max-stack option to limit callchain stack scan

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Message-ID: <52653F6E.2030306@hp.com>
Date:	Mon, 21 Oct 2013 10:51:26 -0400
From:	Waiman Long <waiman.long@...com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v2 3/4] perf-report: add --max-stack option to limit callchain
 stack scan

On 10/18/2013 01:17 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Oct 18, 2013 at 10:38:48AM -0400, Waiman Long escreveu:
>> When callgraph data was included in the perf data file, it may take a
>> long time to scan all those data and merge them together especially
>> if the stored callchains are long and the perf data file itself is
>> large, like a Gbyte or so.
>>
>> The callchain stack is currently limited to PERF_MAX_STACK_DEPTH (127).
>> This is a large value. Usually the callgraph data that developers are
>> most interested in are the first few levels, the rests are usually
>> not looked at.
>>
>> This patch adds a new --max-stack option to perf-report to limit the
>> depth of callchain stack data to look at to reduce the time it takes
>> for perf-report to finish its processing. It trades the presence of
>> trailing stack information with faster speed.
>>
>> The following table shows the elapsed time of doing perf-report on a
>> perf.data file of size 985,531,828 bytes.
>>
>> --max_stack	Elapsed Time	Output data size
>> -----------	------------	----------------
> Please prefix lines like this (------) with a space, otherwise 'git am'
> will chop off everything from that line onwards. Fixing it up now.
>
> - Arnaldo
>
>

Thank for spotting the problem, will fix that in the next version.

-Longman
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