Date: Wed, 14 Apr 2010 22:16:57 -0700 (PDT) From: Paul Zimmerman <paul-zimmerman@sbcglobal.net> To: peterjeremy@acm.org, freebsd-arch@freebsd.org Cc: bruce@cran.org.uk, ed@80386.nl, scottl@samsco.org, matthew.fleming@isilon.com, avg@icyb.net.ua, rwatson@freebsd.org, ivoras@freebsd.org, stefan@fafoe.narf.at, max@love2party.net Subject: Re: likely and unlikely Message-ID: <493092.21442.qm@web80804.mail.mud.yahoo.com>
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On 2010-Mar-21 19:52:40 -0600, Peter Jeremy <peterjeremy () acm ! org> wrote: >I suspect predict_true/predict_false is unlikely to help in most cases. > >What would probably be more useful for Atom would be gcc scheduling >support. This is available in gcc 4.3 (ie GPL3) but not in gcc 4.2. >I've had a look at dumping the gcc 4.3 Atom scheduler into my gcc 4.2 >but the infrastructure has changed sufficiently that this would be a >non-trivial task. (And since it would not be committable, I don't >think it's worth my time). Likewise, implementing scheduling from >scratch in gcc 4.2 would be a non-trivial task. Just FYI, the use of likely/unlikely in the Linux kernel is not for branch prediction. It is a hint to gcc which branch of the if() should be moved out-of-line. The idea is to reduce the cache footprint of the most frequently executed code paths. -- Paul
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