linux-kernel - Re: [PATCH 0/4] perf tools: New comm infrastructure

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Date:	Fri, 13 Sep 2013 14:46:18 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
	David Ahern <dsahern@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 0/4] perf tools: New comm infrastructure

On Fri, Sep 13, 2013 at 03:32:34PM +0900, Namhyung Kim wrote:
> Hi Frederic,
> 
> On Thu, 12 Sep 2013 22:29:39 +0200, Frederic Weisbecker 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.
> 
> I got this:
> 
> ui/browsers/hists.c: In function ‘hists__browser_title’:
> ui/browsers/hists.c:1258:10: error: passing argument 1 of ‘thread__comm_curr’ discards ‘const’ qualifier from pointer target type [-Werror]
> In file included from ui/browsers/../../util/sort.h:24:0,
>                  from ui/browsers/hists.c:11:
> ui/browsers/../../util/thread.h:39:13: note: expected ‘struct thread *’ but argument is of type ‘const struct thread *’
> ui/browsers/hists.c: In function ‘perf_evsel__hists_browse’:
> ui/browsers/hists.c:1581:9: error: passing argument 1 of ‘thread__comm_curr’ discards ‘const’ qualifier from pointer target type [-Werror]
> In file included from ui/browsers/../../util/sort.h:24:0,
>                  from ui/browsers/hists.c:11:
> ui/browsers/../../util/thread.h:39:13: note: expected ‘struct thread *’ but argument is of type ‘const struct thread *’
> ui/browsers/hists.c:1704:10: error: passing argument 1 of ‘thread__comm_curr’ discards ‘const’ qualifier from pointer target type [-Werror]
> In file included from ui/browsers/../../util/sort.h:24:0,
>                  from ui/browsers/hists.c:11:
> ui/browsers/../../util/thread.h:39:13: note: expected ‘struct thread *’ but argument is of type ‘const struct thread *’
> cc1: all warnings being treated as errors
> make: *** [ui/browsers/hists.o] Error 1
> make: *** Waiting for unfinished jobs....

Oops, I'm missing the libs to build the ui, so I didn't see this. Will fix, thanks!

> 
> Thanks,
> Namhyung
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