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

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Date:	Wed, 18 Jul 2012 12:21:52 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Ulrich Drepper <drepper@...il.com>,
	Namhyung Kim <namhyung@...il.com>, acme@...hat.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
Subject: Re: [PATCHv3 0/3] perf tool: Add new event group management

On Tue, Jul 17, 2012 at 09:15:23AM +0200, Stephane Eranian wrote:
> On Mon, Jul 9, 2012 at 1:05 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > On Fri, Jul 06, 2012 at 03:42:54AM +0200, Stephane Eranian wrote:
> > > On Fri, Jul 6, 2012 at 3:32 AM, Ulrich Drepper <drepper@...il.com> wrote:
> > > > On Thu, Jul 5, 2012 at 12:15 PM, Stephane Eranian <eranian@...gle.com> wrote:
> > > >> 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.
> > > >
> > > > In a blue sky world I would have done this.  In fact, this is what I
> > > > tried before reading the sources to find out there is no group support
> > > > so far.  But given that multiple -e options already have a meaning I
> > > > would be hesitant to change this.
> > >
> > > That's why I said you activate grouping via -e only when you have
> > > the --group-events or --group-reads option in front. That would
> > > not change the meaning of the multiple -e when none of those
> > > group options are specified.
> >
> > I discussed this with peter..
> >
> > <peterz> the {} thing allows: 1) multiple groups in a single -e, 2) group attributes
> >
> And what's the value of 1) exactly? What's wrong with passing multiple -e ?
> The only group attribute I can think of would be :u, :k. Not so much typing.
> 
> > as for the leader sampling, we can have the first event to become the leader
> > by default (omit the leader index modifier) and enable the leader sampling by
> > another modifier:
> >
> I don't understand this sentence.
> 
> > <peterz> right, just make it a single 'l' (el not one) to indicate 'leader' sampling
> >
> To me ,this looks a bit of an over-engineered design and it is not based on
> any actual user requests. Don't get me wrong, grouping is useful and required
> but nobody has ever asked for that level of flexibility. The syntax you have
> now is already very rich for my taste.

Well, I personally like the '{}' syntax more than '--group-events or --group-reads
option in front', it feels more user friendly.. anyway, we can easily have both ways.

As for the group attributes and group leader sampling, I don't mind omitting
them at this point and get back to that if we find it useful in future.

jirka
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