From: Con Kolivas <kernel@kolivas.org>
To: Arjan van de Ven <arjan@infradead.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, george@mvista.com
Subject: Re: gettimeofday order of magnitude slower with pmtimer, which is default
Date: Tue, 21 Mar 2006 23:07:59 +1100 [thread overview]
Message-ID: <200603212308.00645.kernel@kolivas.org> (raw)
In-Reply-To: <1142942684.3077.66.camel@laptopd505.fenrus.org>
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
next prev parent reply other threads:[~2006-03-21 12:08 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-20 12:24 gettimeofday order of magnitude slower with pmtimer, which is default bert hubert
2006-03-20 14:50 ` Andreas Mohr
2006-03-20 15:24 ` Con Kolivas
2006-03-21 1:26 ` OGAWA Hirofumi
2006-03-21 0:40 ` kernel
2006-03-21 2:59 ` OGAWA Hirofumi
2006-03-21 3:09 ` Con Kolivas
2006-03-21 8:53 ` Andreas Mohr
2006-03-21 9:06 ` Arjan van de Ven
2006-03-21 11:58 ` Con Kolivas
2006-03-21 12:04 ` Arjan van de Ven
2006-03-21 12:07 ` Con Kolivas [this message]
2006-03-21 19:23 ` john stultz
2006-03-21 21:19 ` OGAWA Hirofumi
2006-03-22 0:21 ` Con Kolivas
2006-03-22 18:49 ` [PATCH] PM-Timer: doesn't use workaround if chipset is not buggy OGAWA Hirofumi
2006-03-22 21:46 ` Andrew Morton
2006-03-23 7:31 ` OGAWA Hirofumi
2006-03-23 7:49 ` Andrew Morton
2006-03-23 17:04 ` Andreas Mohr
2006-03-23 18:21 ` OGAWA Hirofumi
2006-03-30 11:53 ` Andreas Mohr
2006-03-30 15:37 ` OGAWA Hirofumi
2006-03-30 16:02 ` Andreas Mohr
2006-03-25 12:00 ` bert hubert
2006-03-22 19:12 ` gettimeofday order of magnitude slower with pmtimer, which is default Avi Kivity
2006-03-22 19:54 ` OGAWA Hirofumi
2006-03-22 20:05 ` john stultz
2006-03-21 19:34 ` john stultz
-- strict thread matches above, loose matches on Subject: below --
2006-03-21 5:33 Albert Cahalan
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