linux-kernel - Re: [PATCH 1/8] perf callchain: Convert children list to rbtree

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Message-ID: <20131008192242.GA8392@localhost.localdomain>
Date:	Tue, 8 Oct 2013 21:22:45 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 1/8] perf callchain: Convert children list to rbtree

On Tue, Oct 08, 2013 at 11:03:16AM +0900, Namhyung Kim wrote:
> On Wed, 2 Oct 2013 12:18:28 +0200, Frederic Weisbecker wrote:
> > On Thu, Sep 26, 2013 at 05:58:03PM +0900, Namhyung Kim wrote:
> >> From: Namhyung Kim <namhyung.kim@....com>
> >> 
> >> Current collapse stage has a scalability problem which can be
> >> reproduced easily with parallel kernel build.  This is because it
> >> needs to traverse every children of callchain linearly during the
> >> collapse/merge stage.  Convert it to rbtree reduced the overhead
> >> significantly.
> >> 
> >> On my 400MB perf.data file which recorded with make -j32 kernel build:
> >> 
> >>   $ time perf --no-pager report --stdio > /dev/null
> >> 
> >> before:
> >>   real	6m22.073s
> >>   user	6m18.683s
> >>   sys	0m0.706s
> >> 
> >> after:
> >>   real	0m20.780s
> >>   user	0m19.962s
> >>   sys	0m0.689s
> >> 
> >> During the perf report the overhead on append_chain_children went down
> >> from 96.69% to 18.16%:
> >> 
> >>   -  18.16%  perf  perf                [.] append_chain_children
> >>      - append_chain_children
> >>         - 77.48% append_chain_children
> >>            + 69.79% merge_chain_branch
> >>            - 22.96% append_chain_children
> >>               + 67.44% merge_chain_branch
> >>               + 30.15% append_chain_children
> >>               + 2.41% callchain_append
> >>            + 7.25% callchain_append
> >>         + 12.26% callchain_append
> >>         + 10.22% merge_chain_branch
> >>   +  11.58%  perf  perf                [.] dso__find_symbol
> >>   +   8.02%  perf  perf                [.] sort__comm_cmp
> >>   +   5.48%  perf  libc-2.17.so        [.] malloc_consolidate
> >> 
> >> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> >> Cc: Jiri Olsa <jolsa@...hat.com>
> >> Cc: Frederic Weisbecker <fweisbec@...il.com>
> >> Link: http://lkml.kernel.org/n/tip-d9tcfow6stbrp4btvgs51y67@git.kernel.org
> >> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> >
> > Have you tested this patchset when collapsing is not used?
> > There are fair chances that this patchset does not only improve collapsing
> > but also callchain insertion in general. So it's probably a win in any case. But
> > still it would be nice to make sure that it's the case because we are getting
> > rid of collapsing anyway.
> >
> > The test that could tell us about that is to run "perf report -s sym" and compare the
> > time it takes to complete before and after this patch, because "-s sym" shouldn't
> > involve collapses.
> >
> > Sorting by anything that is not comm should do the trick in fact.
> 
> Yes, I have similar result when collapsing is not used.  Actually when I
> ran "perf report -s sym", the performance improves higher since it'd
> insert more callchains in a hist entry.

Great! I'll have a closer look and review on the callchain patches then. Please
resend these along the comm batch.

Thanks again!
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