linux-kernel - Re: [tip:perf/core] events: Rename TRACE_EVENT_TEMPLATE() to DECLARE_EVENT

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Date:	Thu, 26 Nov 2009 19:12:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	penberg@...helsinki.fi, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] events: Rename TRACE_EVENT_TEMPLATE() to
 DECLARE_EVENT_CLASS()


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Thu, Nov 26, 2009 at 09:45:30AM -0500, Steven Rostedt wrote:
> > On Thu, 2009-11-26 at 09:40 +0100, Ingo Molnar wrote:
> > > * Steven Rostedt <rostedt@...dmis.org> wrote:
> > > 
> > 
> > > > I would like to hear what others think about this change before we go 
> > > > ahead and implement it.
> > > 
> > > You mean TRACE_EVENT() -> DEFINE_SINGLE_EVENT()? Sure, we want todo it 
> > > in a more quiet moment of the kernel cycle, not now.
> > > 
> > > (TRACE_EVENT_TEMPLATE OTOH has existed for just a few days so it's not a 
> > > problem.)
> > 
> > Yes the template name is new, I'm not talking about that on
> > particularly.
> 
> I personally don't mind much about the name, especially between class 
> and template. Both make equally sense to me.
> 
> But DECLARE sounds like a misnomer here (like DEFINE_EVENT somehow) as 
> TRACE_EVENT, DEFINE_EVENT and TRACE_EVENT_TEMPLATE all behave either 
> as a declaration or a definition, depending on the CREATE_TRACE_POINT 
> macro.

DECLARE_EVENT_CLASS() doesnt really define an event visible to the user 
yet though. It defines functions internally (to be used by the real 
definition of the event) - but not visible externally really.

So the real 'definition' of an event happens with DEFINE_EVENT() - in 
the logical model of this.

So the logical model is clear:

   DECLARE_EVENT_CLASS(class);

    DEFINE_EVENT(class, event1);
    DEFINE_EVENT(class, event2);
    DEFINE_EVENT(class, event3);
    ...

  # later:
  # DEFINE_STANDALONE_EVENT(event)

And the logical model is what matters: that's what developers will use. 
They'll use these constructs based on the logical model, nobody sane 
will look into the CPP magic ;-)

And yes, we occasionally have to revisit our naming choices - especially 
when mistakes/misnomers become apparent.

Thanks,

	Ingo
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