linux-kernel - Re: [PATCH 3/3] perf, tool: Add new event group management

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Date:	Tue, 20 Mar 2012 19:44:41 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	acme@...hat.com, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] perf, tool: Add new event group management

On Tue, 2012-03-20 at 19:15 +0100, Jiri Olsa wrote:
> Examples (first event in brackets is group leader):
> 
>   # 1 group (cpu-clock,task-clock)
>   perf record --group -e cpu-clock,task-clock ls
>   perf record --group parsed -e cpu-clock,task-clock ls
> 
>   # 2 groups (cpu-clock,task-clock) (minor-faults,major-faults)
>   perf record --group parsed -e cpu-clock,task-clock \
>    -e minor-faults,major-faults ls
> 
>   # 1 group (cpu-clock,task-clock,minor-faults,major-faults)
>   perf record --group -e cpu-clock,task-clock \
>    -e minor-faults,major-faults ls
> 
>   # 2 groups (cpu-clock,task-clock) (minor-faults,major-faults)
>   perf record --group parsed -e cpu-clock,task-clock \
>    -e minor-faults,major-faults -e instructions ls
> 
>   # 1 group (cpu-clock,task-clock,minor-faults,major-faults,instructions)
>   perf record --group -e cpu-clock,task-clock \
>    -e minor-faults,major-faults -e instructions ls 

I can't help but dislike the --group/--group parsed thing...

How about something like:

  event_group = "{", events, "}" , [ ":", event_group_mod ]

Such that you can write things like:

  perf record -e "{cpu-clock,cache-misses,cache-references}"

  perf stat -e "{cpu-clock,cycles},{cpu-clock,cache-misses,cache-references}"
  perf stat -e "{cpu-clock,cycles}" -e "{cpu-clock,cache-misses,cache-references}"

I'm not sure what the current behaviour of --group is, if you create a
group like this, do they all sample?

If so, we need some option like:

  perf record -e "{cpu-clock,cache-misses,cache-references}:1"

to mean, only sample on cpu-clock but use PERF_SAMPLE_READ and
PERF_FORMAT_GROUP to read all siblings on every cpu-clock sample.

Now the disadvantage is that {} needs quotes on bash, the advantage is
that its completely natural on how to construct groups, without weird
--group/--group parsed. Also it provides a place for group modifiers.
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