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Subject: Re: gettimeofday order of magnitude slower with pmtimer, which is
	default
From: Arjan van de Ven <arjan@infradead.org>
To: Con Kolivas <kernel@kolivas.org>
Cc: Andreas Mohr <andi@rhlx01.fht-esslingen.de>,
       OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
       bert hubert <bert.hubert@netherlabs.nl>, linux-kernel@vger.kernel.org,
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Date: Tue, 21 Mar 2006 13:04:44 +0100
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On Tue, 2006-03-21 at 22:58 +1100, Con Kolivas wrote:
> On Tuesday 21 March 2006 19:53, Andreas Mohr wrote:
> > (and the fact that invoking a function pointer should be similarly
> > expensive to a conditional) I don't think it's useful.
> 
> Is 
> 
> *blah();
> 
> as expensive as
> 
> if (conditional)
> 	blah();
> 
> I don't know the answer. I just know cmp is expensive. Comments?

function pointer is usually MORE expensive.
for if() the processor has a change to predict the branch right, while
call <register> (which is what function pointer calls end up being) are
basically always mispredicted unless you have a really really fancy
branch predictor... 

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