linux-kernel - Re: [PATCHv3 0/3] perf tool: Add new event group management

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Date:	Fri, 6 Jul 2012 03:06:41 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...il.com>,
	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	andi@...stfloor.org, drepper@...il.com
Subject: Re: [PATCHv3 0/3] perf tool: Add new event group management

On Thu, Jul 5, 2012 at 6:44 PM, Arnaldo Carvalho de Melo
<acme@...hat.com> wrote:
> Em Thu, Jul 05, 2012 at 06:15:20PM +0200, Stephane Eranian escreveu:
>> On Mon, Jul 2, 2012 at 3:33 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>> > perf, tool: Enable sampling on specified event group leader
>> >
>> > Adding the functionality to the group modifier event syntax.
>> > Allowing user to select leader event inside the group using
>> > event index (command line event position in the group).
>> >
>> > Following example selects e2 as leader:
>> >   -e '{e1,e2,e3,e4}:2'
>> >
>> I don't understand why you actually need the :2 suffix. There can
>> only be one leader. So assume it is the first one. Users have to
>> know the first one is the leader which seems like a natural thing
>> to do for me. It would make you syntax less ugly than it already
>> is.
>
> Agreed, looks like creeping featurism.
>
>> I would have thought you could enable this with a simple
>> cmdline option which changes the way you interpret the
>> multiple -e options:
>>
>> perf record --group-reads -e e1,e2,e3 -e e4,e5,e6 .....
>>
>> Would setup the group leaders (e1, e4) for 2 groups.
>> NO curly braces, no : needed.
>
> Yeah, curly braces needed just when one wants to add group wide
> modifiers.
And even, in that case that seems overkill too.
You can simply repeat the modifier on each event. A group cannot
big that big. It is limited in size by the number of physical counters
plus the events constraints.
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