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

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Message-ID: <CABPqkBTUJhnCNM_qMAbmHSam4W+j6Vq+X+9awEyOJn1nCt9aFg@mail.gmail.com>
Date:	Tue, 5 Nov 2013 15:04:09 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Jiri Olsa <jolsa@...hat.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 5, 2013 at 3:00 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> 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, ...
>
Somewhat. It is used to make parsing easy for the perf stat output.
But if you have a script that was expecting 2222267,cycles and now
is getting 222267,?,cycles. Things will break.


>   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
>
But then, it is not so good for the -x option to get ' ' in the csv output.

>>
>> 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
>
Well, that's what I had initially. But then people thought it was more
natural to have in before the event. I agreed with that.

I almost have the --show-unit option working now. I think we should
go with that.
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