linux-kernel - Re: [PATCH 2/2] perf-report: add --max-stack option to limit callchain stack scan

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Date:	Thu, 17 Oct 2013 12:28:43 -0400
From:	Waiman Long <waiman.long@...com>
To:	David Ahern <dsahern@...il.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	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>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 2/2] perf-report: add --max-stack option to limit callchain
 stack scan

On 10/16/2013 11:01 PM, David Ahern wrote:
> On 10/16/13 1:59 PM, Waiman Long wrote:
>> 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.
>
> I like the patch. I have a similar option in my perf-sched-timehist 
> command, and I have a patch somewhere for perf-script.
>
> It would be even better to pass this arg kernel side and limit the 
> stack depth at data collection time.
>

That will require option a similar option on the record side. However, 
the overhead of collecting more stack ip address isn't as high as that 
in the report side.

> ---8<---
>
>> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
>> index 72eae74..d90d04a 100644
>> --- a/tools/perf/builtin-report.c
>> +++ b/tools/perf/builtin-report.c
>> @@ -37,6 +37,12 @@
>>
>>   #include <linux/bitmap.h>
>>
>> +/*
>> + * 2-level stringification macro to enable stringification of macro 
>> value
>> + * */
>> +#define    __to_string(x)    #x
>> +#define    STRINGIFY(x)    __to_string(x)
>
> These 2 lines should be somewhere else -- like util/util.h

I will move that to a common header file.

>
> ---8<---
>
>> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
>> index 2122141..2725aca 100644
>> --- a/tools/perf/builtin-top.c
>> +++ b/tools/perf/builtin-top.c
>> @@ -771,7 +771,8 @@ static void perf_event__process_sample(struct 
>> perf_tool *tool,
>>               sample->callchain) {
>>               err = machine__resolve_callchain(machine, evsel,
>>                                al.thread, sample,
>> - &parent, &al);
>> + &parent, &al,
>> +                             PERF_MAX_STACK_DEPTH);
>>               if (err)
>>                   return;
>>           }
>
> Why not add the option to perf-top as well? copy-paste.

I had thought about it, but I decided to wait for feedback before doing 
it. I will make that change in the next version.

-Longman

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