* Frederic Weisbecker <fweis...@gmail.com> wrote:
> The way we handle hists sorted by comm is to first gather them by tid
> then in the end merge/collapse hists that end up with the same comm.
>
> But merging hists has shown some performances issues, especially with
> callchain where the operation can be very heavy.
>
> So this new comm infrastructure aims at removing comm collapses. It
> brings two features:
>
> 1) Keep track of comms lifecycle by storing timestamps when the comms
> are set. This way we can map the precise comm to any thread:time couple.
> This only works if the PERF_SAMPLE_ID comes along comm and fork events,
> otherwise we only track the latest comm set for a thread.
>
> This can provide us more precise comm sorted hists by distinguishing pre
> and post exec timeframes into seperate hists for a single thread.
>
> Note that although the comm infrastructure is ready to do this, I
> haven't yet made the perf tools support that. It's a TODO entry.
>
> 2) Allocate comms only once instead of duplicating them for all threads
> sharing a same one. Two threads having the same comm should now point to
> the same string. As a result we can compare hists thread comm by
> address.
>
> The big upside is that we can now live sort comm hists instead of
> collapsing them in the end of the processing.
>
> I've seen very nice performance results on perf report. Roughly a 1.5x
> to 2x on perf report default stdio output with callchains.
>
> You can try this branch:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> perf/comm
>
> May be merging that with Namhyung callchains patches could provide some
> cumulative nice results.
It would be nice to try Linus's testcase, which is, in essence a kernel
build profile:
make defconfig
perf record -g make -j64 bzImage
and to make sure that it can analyze the data in same, non-annoying
runtimes. What I saw was 30 minutes of runtime - a 2x improvement is not
nearly enough, 15 minutes is still an eternity.
Thanks,
Ingo
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