linux-kernel - Re: [PATCH 1/3] Fix Unlikely(x) == y

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Message-ID: <20080218103320.41cf096f@laptopd505.fenrus.org>
Date:	Mon, 18 Feb 2008 10:33:20 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Valdis.Kletnieks@...edu
Cc:	David Howells <dhowells@...hat.com>,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	Adrian Bunk <bunk@...nel.org>, Roel Kluin <12o3l@...cali.nl>,
	lkml <linux-kernel@...r.kernel.org>, cbe-oss-dev@...abs.org,
	linuxppc-dev@...abs.org, Willy Tarreau <w@....eu>
Subject: Re: [PATCH 1/3] Fix Unlikely(x) == y

On Mon, 18 Feb 2008 13:11:06 -0500
Valdis.Kletnieks@...edu wrote:

> On Mon, 18 Feb 2008 14:27:10 GMT, David Howells said:
> 
> > __builtin_expect() is useful on FRV where you _have_ to give each
> > branch and conditional branch instruction a measure of probability
> > whether the branch will be taken.
> 
> What does gcc do the 99.998% of the time we don't have
> likely/unlikely coded?

see Andi's email.
It gets the exact same hints that 95%+ of the kernels unlikely/likely get you,
because the heuristics in it are usually the same as the kernel programmers 
heuristics.


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