Subject: Re: [tip:perf/core] tracing: Add DEFINE_EVENT(),
 DEFINE_SINGLE_EVENT() support to docbook
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Ingo Molnar <mingo@elte.hu>, mingo@redhat.com, hpa@zytor.com,
       linux-kernel@vger.kernel.org, randy.dunlap@oracle.com,
       wcohen@redhat.com, fweisbec@gmail.com, tglx@linutronix.de,
       jbaron@redhat.com, mhiramat@redhat.com,
       linux-tip-commits@vger.kernel.org, Christoph Hellwig <hch@lst.de>
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Date: Wed, 02 Dec 2009 13:19:47 -0500
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On Wed, 2009-12-02 at 13:06 -0500, Mathieu Desnoyers wrote:
> *
> Hrm. I wonder if having DEFINE_EVENT_CLASS is really worth having,
> considering that it really just does 2 things at once and may be
> confusing.

We keep it because that's what TRACE_EVENT currently is. It would suck
to have to replace every TRACE_EVENT there is now with a
DECLARE_EVENT_CLASS and DEFINE_EVENT. Although this would push
developers into using classes.

> 
> I would have thought amongst the lines of the following as main API
> (note: "SKETCH" is only a proposal. The idea is to do _not_ use
> declare/define, as it's really something _different_ than what people
> are expecting!)
> 
> SKETCH_EVENT_CLASS()
> 
> SKETCH_EVENT()
> 
> Which would use only DECLARE, or both DECLARE and DEFINE depending if
> CREATE_TRACE_POINTS is set. I see the DECLARE/DEFINE more as the
> "low-level" macros that are actually selected by CREATE_TRACE_POINTS:
> 
> DECLARE_EVENT_CLASS : only performs event class declarations (macros,
> inlines...)
> 
> DECLARE_EVENT : only performs event instance declarations (macros,
> inlines, ...). Depends on the DECLARE_EVENT_CLASS().
> 
> DEFINE_EVENT_CLASS : create instances of template functions.
> 
> DEFINE_EVENT : create event tracepoint functions. Depends on
> DEFINE_EVENT_CLASS().
> 
> This way, it should make digging into the generation system internals
> headhache-free. ;) I think we should really avoid re-using terms people
> are familiar with for things that have a semantic intrincially different
> than what people come to expect.

Egad No! It would make it a living nightmare. The internals reuse the
define macro, and there's no intermediate. By changing the
DECLARE_EVENT_CLASS to another name (SKETCH_EVENT_CLASS) we would have
to add something like this:

#define SKETCH_EVENT_CLASS(name, proto, args, tstruct, print) \
	DECLARE_EVENT_CLASS(name, PARAMS(proto), PARAMS(args),\
		PARAMS(tstruct), PARAMS(print))

We don't have a intermediate or "low level" macro in use here. Whatever
we give to the user is what we use.


I think the kernel developers are smart enough to figure out that these
macros are not a typical DECLARE/DEFINE that is elsewhere. But I think
using the DECLARE/DEFINE names will give them a better idea of what is
happening than to make up something completely new.

-- Steve

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