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

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Date:	Wed, 16 Oct 2013 21:01:04 -0600
From:	David Ahern <dsahern@...il.com>
To:	Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	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 10/16/13 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.

---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

---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.

David
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