From owner-freebsd-hackers@FreeBSD.ORG Mon Feb 16 05:51:30 2004 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id DD09C16A4CE for ; Mon, 16 Feb 2004 05:51:30 -0800 (PST) Received: from tx0.oucs.ox.ac.uk (tx0.oucs.ox.ac.uk [129.67.1.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id B746B43D1F for ; Mon, 16 Feb 2004 05:51:30 -0800 (PST) (envelope-from colin.percival@wadham.ox.ac.uk) Received: from scan0.oucs.ox.ac.uk ([129.67.1.162] helo=localhost) by tx0.oucs.ox.ac.uk with esmtp (Exim 4.24) id 1Asj9l-0001wn-Fp for freebsd-hackers@freebsd.org; Mon, 16 Feb 2004 13:51:29 +0000 Received: from rx0.oucs.ox.ac.uk ([129.67.1.161]) by localhost (scan0.oucs.ox.ac.uk [129.67.1.162]) (amavisd-new, port 25) with ESMTP id 07203-07 for ; Mon, 16 Feb 2004 13:51:29 +0000 (GMT) Received: from gateway.wadham.ox.ac.uk ([163.1.161.253]) by rx0.oucs.ox.ac.uk with smtp (Exim 4.24) id 1Asj9l-0001wc-2H for freebsd-hackers@freebsd.org; Mon, 16 Feb 2004 13:51:29 +0000 Received: (qmail 31321 invoked by uid 0); 16 Feb 2004 13:51:29 -0000 Received: from colin.percival@wadham.ox.ac.uk by gateway by uid 71 with qmail-scanner-1.16 (sweep: 2.14/3.71. spamassassin: 2.53. Clear:. Processed in 1.763373 secs); 16 Feb 2004 13:51:29 -0000 X-Qmail-Scanner-Mail-From: colin.percival@wadham.ox.ac.uk via gateway X-Qmail-Scanner: 1.16 (Clear:. Processed in 1.763373 secs) Received: from dhcp1131.wadham.ox.ac.uk (HELO piii600.wadham.ox.ac.uk) (163.1.161.131) by gateway.wadham.ox.ac.uk with SMTP; 16 Feb 2004 13:51:27 -0000 Message-Id: <6.0.1.1.1.20040216134828.0390bfa0@imap.sfu.ca> X-Sender: cperciva@imap.sfu.ca (Unverified) X-Mailer: QUALCOMM Windows Eudora Version 6.0.1.1 Date: Mon, 16 Feb 2004 13:51:25 +0000 To: Trent Nelson From: Colin Percival In-Reply-To: <20040215164231.GA54709@teleri.net> References: <20040215164231.GA54709@teleri.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed cc: freebsd-hackers@freebsd.org Subject: Re: Branch prediction X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 Feb 2004 13:51:31 -0000 At 16:42 15/02/2004, Trent Nelson wrote: >does the old adage of "always predict >false" still hold true the first time a branch is encountered? Most processors predict that forward branches are not taken, and backward branches are taken (since backward branches occur most often in loops). Of course, some processors now have hints (conditional-jump- which-is-usually-taken, conditional-jump-which-is-usually-not- taken, etc.) Colin Percival