linux-kernel - Re: [PATCH 35/40] perf record: Synthesize COMM event for a command line workload

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Date:	Wed, 20 May 2015 08:56:58 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 35/40] perf record: Synthesize COMM event for a command
 line workload

On Tue, May 19, 2015 at 05:18:54PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, May 19, 2015 at 09:49:03PM +0200, Jiri Olsa escreveu:
> > On Wed, May 20, 2015 at 12:12:45AM +0900, Namhyung Kim wrote:
> > 
> > SNIP
> > 
> > > > > > 
> > > > > > This looks reasonable, but I think it probably needs to be done
> > > > > > somewhere in perf_evlist__prepare_workload() or
> > > > > > perf_evlist__start_workload(), as this affects other tools as well, like
> > > > > > 'top', 'trace' and any other that may want to do this start-workload use
> > > > > > case.
> > > > > 
> > > > > Hmm.. I need to look at this again as it only affects on processing
> > > > > indexed data files which used to have a separate missing threads tree.
> > > > 
> > > > Humm, you're thinking about where you managed to reproduce the problem,
> > > > I am thinking outside indexing, etc, i.e. by definition we either enable
> > > > the event before we fork, so that we get the PERF_RECORD_FORK/COMM or we
> > > > synthesize it either from /proc or directly (preferred) if we decide to
> > > > do it after the fork/exec, right?
> > > 
> > > But as I said before, later COMM event will override thread->comm to a
> > > proper string as long as it can find a matching thread.  So I think it
> > > has no problem in the current code.
>  
> > I can see the issue in the current script code and the patch cured it ;-)
> 
> Exactly, this is my point, this is not something new :-)

Ah, okay.  The perf script shows samples before processing comm events
while perf report shows after processing all events.

But to move it under generic place like perf_evlist__{prepare,start}_
workload(), it seems we need to pass an additional callback and data.

I'll try to write a patch.

Thanks,
Namhyung

> 
> - Arnaldo
>  
> > before:
> > 
> > [jolsa@...va perf]$ ./perf record -o - true | ./perf script 
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.000 MB - ]
> >           :29236 29236 350869.479255:          1 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >           :29236 29236 350869.479260:          1 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >           :29236 29236 350869.479261:          7 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >           :29236 29236 350869.479263:        122 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >           :29236 29236 350869.479264:       2303 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >           :29236 29236 350869.479266:      49582 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             true 29236 350869.479283:    1041734 cycles:  ffffffff81190a4a perf_output_begin ([kernel.kallsyms])
> > 
> > after:
> > 
> > [jolsa@...va perf]$ ./perf record -o - true | ./perf script 
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.000 MB - ]
> >             perf 28041 350801.438466:          1 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             perf 28041 350801.438471:          1 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             perf 28041 350801.438472:          7 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             perf 28041 350801.438473:        140 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             perf 28041 350801.438475:       3721 cycles:  ffffffff8105e8aa native_write_msr_safe ([kernel.kallsy
> >             perf 28041 350801.438476:      94744 cycles:  ffffffff8118e270 perf_event_comm ([kernel.kallsyms])
> >             true 28041 350801.438508:    1604677 cycles:  ffffffff811d0781 do_mmap_pgoff ([kernel.kallsyms])
> > 
> > jirka
> --
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