linux-kernel - Re: [perf] howto switch from pfmon

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Date:	Tue, 23 Jun 2009 16:51:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Brice Goglin <Brice.Goglin@...ia.fr>,
	Mike Galbraith <efault@....de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, paulus@...ba.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [perf] howto switch from pfmon


* Brice Goglin <Brice.Goglin@...ia.fr> wrote:

> Ingo Molnar wrote:
> > You can also do a profile with such events:
> >
> >   perf record -f -e r1000ffe0 ./hackbench 10
> >
> > and look at it via 'perf report'.
> >   
> 
> I am not sure what the perf.data profile file contains but 'perf 
> report' only shows percentages. Is there a way to get a 'perf 
> stat'-like output from 'perf report'? Or maybe just have a -f 
> option in 'perf stat' to send the output into a file (with the PID 
> in the name).

It's not yet possible but it's a very good feature request.

> By the way, there's a typo in the description in 
> tools/perf/Documentation/perf-report.txt, you want s/via perf 
> report/via perf record/

thanks, fixed and pushed out. You can generally find the latest 
'perf' stuff at:

  http://people.redhat.com/mingo/tip.git/README

> > [ Note, there's no need to specify any --follow-* flags as that is
> >   implicit in 'perf'. (and you'll probably also notice that perf
> >   stat is a lot faster at following fast-forking or
> >   context-switching workloads than is pfmon, because it's not ptrace
> >   based.) ]
> 
> What about threads? I didn't find any way to get per-thread 
> counters.
> 
> Ideally, I'd like to be able to see no perf-related output on 
> stdout/stderr at runtime, and later have a look at per-thread 
> counters like 'perf stat' does at runtime.

That's not possible yet either, but makes a lot of sense.

How many threads does your workload typically run, and how do you 
get their stats displayed?

Per thread info is currently available in the profile output:

   perf report --sort comm,pid,symbol

But it would be nice to either extend perf report with a --stat 
option:

   perf report --stat

or to extend perf stat to take an input file via -i:

   perf stat -i perf.data

	Ingo
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