Date: Tue, 16 Mar 2010 21:50:33 +0000 From: Bruce Cran <bruce@cran.org.uk> To: freebsd-arch@freebsd.org Cc: Max Laier <max@love2party.net> Subject: Re: likely and unlikely Message-ID: <201003162150.33852.bruce@cran.org.uk> In-Reply-To: <20100313200155.O22734@delplex.bde.org> References: <hndbed$vok$1@dough.gmane.org> <201003121513.38721.max@love2party.net> <20100313200155.O22734@delplex.bde.org>
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On Saturday 13 March 2010 09:24:39 Bruce Evans wrote: > These macros may have useful 15-25 years ago for i386, i486 and Pentium1, > since CPU branch predictors were either nonexistent or not so good. > After that, CPU branch predictors became quite good. The macros should > have been mostly unused 15-25 years ago too, since they optimize for > unreadability and unwritability. Fortunately they are rarely used in > FreeBSD. They were imported from NetBSD in 2003 where they are used > more (306 instances in 2005 NetBSD /sys vs 28 instances in 2004 FreeBSD > /sys; there are 2208 instances of likely() in 2004 linux-2.6.10). The Cell powerpc processor doesn't have a dynamic branch prediction unit. Quite a few articles recommend using __builtin_expect to improve performance. -- Bruce Cran
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