linux-kernel - Re: [PATCH 4/4] trace: profile all if conditionals

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Message-ID: <20081123123730.GI29663@elte.hu>
Date:	Sun, 23 Nov 2008 13:37:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	peterz@...radead.org, tytso@....edu, arjan@...radead.org,
	srostedt@...hat.com
Subject: Re: [PATCH 4/4] trace: profile all if conditionals


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Fri, 21 Nov 2008, Andrew Morton wrote:
> > >
> > > +#define if(cond) if (__builtin_constant_p((cond)) ? !!(cond) :		\
> > 
> > wheee...
> > 
> > Now how are you going to profile ?:, while, for(;expr;), etc? ;)

btw., there's hardware driven branch tracing and profiling in the 
works too, which captures all conditionals - including loops. Stay 
tuned :)

> I don't know. Give me a few months, I'll figure out a way ;-)

also loops generally have a more static (hence less interesting) 
prediction pattern - while for branches we frequently have a "should 
this branch be made likely/unlikely in the fastpath" question.

	Ingo
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