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From: Con Kolivas <kernel@kolivas.org>
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: gettimeofday order of magnitude slower with pmtimer, which is default
Date: Tue, 21 Mar 2006 23:07:59 +1100
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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,
       george@mvista.com
References: <20060320122449.GA29718@outpost.ds9a.nl> <200603212258.46265.kernel@kolivas.org> <1142942684.3077.66.camel@laptopd505.fenrus.org>
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On Tuesday 21 March 2006 23:04, Arjan van de Ven wrote:
> 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...

Thanks! That's something I've been trying to find good info on.

Cheers,
Con
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