linux-kernel - Re: [RFC/PATCH] perf record: Save build-id of DSO in callchains

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Date:	Mon, 23 Mar 2015 08:22:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC/PATCH] perf record: Save build-id of DSO in callchains


* Namhyung Kim <namhyung@...nel.org> wrote:

> Currently the build-id only recorded for sampled location, but in
> order to correctly view/annotate callchains it might need the
> build-id's of callchains too.  I guess this choice was due to a
> performance impact on the post-processing at perf record time.
> 
> Add a new option --buildid-callchain to record this info.
> 
> $ perf record -o xxx -g -- perf > /dev/null
> $ perf buildid-list -i xxx
> 6ebcee76c4b04895598b4df86ec445c49fc137a2 /lib/modules/3.18.6-1-ARCH/build/vmlinux
> fc0759b71584d2513b04f1b530965a61b5e499e2 /usr/lib/ld-2.21.so
> 
> $ perf record -o yyy -g --buildid-callchain -- perf > /dev/null
> $ perf buildid-list -i yyy
> 6ebcee76c4b04895598b4df86ec445c49fc137a2 /lib/modules/3.18.6-1-ARCH/build/vmlinux
> 4235ae90856f98d2746529648a3339ebfa6ede43 /home/namhyung/project/linux/tools/perf/perf
> fc0759b71584d2513b04f1b530965a61b5e499e2 /usr/lib/ld-2.21.so
> 9ac81172d5ff96f40d984fe7c10073a98f1a6b2e /usr/lib/libc-2.21.so
> 864583bb881db1d260660a30a51b3f5022cd538b /usr/lib/libnuma.so.1.0.0

Just curious, could you try to measure the performance impact of this 
change?

Also, unless the performance (or file size) effect is horrible, I 
think this flag should be implicitly set by -g.

99.999% of users won't know about this flag, and will see broken 
annotations!

Thanks,

	Ingo
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