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SubjectRe: [PATCH 1/8] perf callchain: Convert children list to rbtree
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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@lge.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@linux-foundation.org>
>> Cc: Jiri Olsa <jolsa@redhat.com>
>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>> Link: http://lkml.kernel.org/n/tip-d9tcfow6stbrp4btvgs51y67@git.kernel.org
>> Signed-off-by: Namhyung Kim <namhyung@kernel.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.

Thanks,
Namhyung


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