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Date: Sun, 23 Nov 2008 13:37:30 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       tglx@linutronix.de, peterz@infradead.org, tytso@mit.edu,
       arjan@infradead.org, srostedt@redhat.com
Subject: Re: [PATCH 4/4] trace: profile all if conditionals
Message-ID: <20081123123730.GI29663@elte.hu>
References: <20081121071213.365288293@goodmis.org> <20081121071328.462456268@goodmis.org> <20081121152030.7024971e.akpm@linux-foundation.org> <alpine.DEB.1.10.0811211832460.7797@gandalf.stny.rr.com>
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* Steven Rostedt <rostedt@goodmis.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