linux-kernel - Re: [tip:perf/urgent] perf sched: Fix list of events, dropping unsupported ':r' modifier

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Message-ID: <20110803121119.GC5768@somewhere.redhat.com>
Date:	Wed, 3 Aug 2011 14:11:21 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, eranian@...gle.com,
	linux-kernel@...r.kernel.org, acme@...hat.com,
	robert.richter@....com, tglx@...utronix.de,
	cjashfor@...ux.vnet.ibm.com, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf sched: Fix list of events, dropping
 unsupported ':r' modifier

On Wed, Aug 03, 2011 at 02:05:35PM +0200, Peter Zijlstra wrote:
> On Wed, 2011-08-03 at 13:57 +0200, Frederic Weisbecker wrote:
> > On Wed, Aug 03, 2011 at 01:42:21PM +0200, Peter Zijlstra wrote:
> > > On Wed, 2011-08-03 at 13:37 +0200, Frederic Weisbecker wrote:
> > > > On Wed, Aug 03, 2011 at 12:59:21PM +0200, Peter Zijlstra wrote:
> > > > > On Fri, 2011-01-14 at 07:25 +0000, tip-bot for Stephane Eranian wrote:
> > > > > > Looks to me like the :r modifier is not supported anymore, so remove it from
> > > > > > the list of events. 
> > > > > 
> > > > > acme, why is that anyway? -R is a fun way to save some typing, but not
> > > > > supporting :r anymore takes away the option of not getting
> > > > > PERF_SAMPLE_RAW output for every event.
> > > > 
> > > > Because it was very non obvious for people to select this -R or :r
> > > > every time they wanted to use trace events for tracing. I think
> > > > there was complaints about that. Moreover nobody seemed to use
> > > > trace events for non-tracing (perf report, top, annotate, ...)
> > > > so we decided to always have RAW records so that it works for
> > > > every cases...unless we lose events because of that.
> > > > 
> > > > We can still bring an option to force disabling of raw records.
> > > 
> > > That just doesn't compute, they still have to use -R, so what's the harm
> > > in also having :r?
> > 
> > Nope -R is the default/forced behaviour already.
> > But even if it wasn't I don't see much the point of ":r". Who wants
> > to run two trace events and only record the traces of one?
> 
> [root@...tmere linux-2.6]# grep raw_samples tools/perf/builtin-record.c | head -1
> static bool                     raw_samples                     =  false;
> 
> is what tip/master is showing me..

Look at tools/perf/util/parse-events.c:parse_single_tracepoint_event()

> 
> > > Also taking away options just because it confuses people sounds like
> > > gnome, lets just not go there.
> > 
> > You're right but options should be there only to be able to override
> > sane default common uses. And not the opposite. And the common use
> > of trace events is for tracing.
> > 
> > We should rather enable tracing by default and disable it through
> > an option. Like --no-trace or so.
> 
> you smoking some expensive stuff, right?
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