linux-kernel - Re: [RFC][PATCH 1/2 v2] tracing: Add TRACE_EVENT

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Message-ID: <1291390727.3228.10.camel@gandalf.stny.rr.com>
Date:	Fri, 03 Dec 2010 10:38:47 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC][PATCH 1/2 v2] tracing: Add TRACE_EVENT_CONDITIONAL()

On Fri, 2010-12-03 at 10:27 -0500, Mathieu Desnoyers wrote:

> > >   TP_CONDITION(unlikely(someparam)),
> > 
> > I actually think this is an abuse of "unlikely".
> 
> Why are you considering this an abuse ?

Because it is overused. I would rather get rid of most unlikely()'s
because they are mostly meaningless. Just run the unlikely profiler, and
you will see a large number of them are just plain incorrect.

Adding them here probably doesn't do any good. The only reason for this
TP_CONDITION() is to ignore those cases that it just does not make sense
to trace. Like a wake up tracepoint that does not wake anything up. No
need for "unlikely" or "likely", by trying to do that, you will most
likely get it wrong.

	unlikely(use_likely_correctly)

-- Steve

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