linux-kernel - Re: [PATCH v4 2/4] perf stat: add event unit and scale support

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Date:	Tue, 5 Nov 2013 15:00:30 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH v4 2/4] perf stat: add event unit and scale support

On Tue, Nov 05, 2013 at 02:34:45PM +0100, Stephane Eranian wrote:
> Hi,
> 
> One thing I realized while testing is that we cannot simply add the
> unit printout like that.
> This may break all the scripts people may have written to parse the
> output of perf stat.

isn't it what the -x output is meant for?

  perf stat -x, ...

  1.738605,task-clock
  367,context-switches
  0,cpu-migrations
  272,page-faults
  6722006,cycles
  2592661,stalled-cycles-frontend
  1935855,stalled-cycles-backend
  4324013,instructions
  823229,branches
  11192,branch-misses

> I think we need to make the display of the unit optional. If I do:
>    $ perf stat -e cycles ls
> 
> The output should remain as it was before and not show:
> $ perf stat -e cycles ls
>       22782847475 ? cycles

maybe we should display just space ' ' instead
of the '?' ...seems confusing

> 
> So I think we need a --show-unit option. It would be off by default.
> Of course doing this causes a mess with the current code because
> of all the various printf() in builtin-stat.c but I think it is better for
> the end user.
> 
> Any opinion?

I haven't checked by I think we changed the default perf stat
output in the past without any fuzz

maybe just keep the -x output or add the unit
to the end of the line

jirka
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