From owner-freebsd-amd64@FreeBSD.ORG Fri May 13 04:39:04 2005 Return-Path: Delivered-To: freebsd-amd64@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D9EB416A4CE for ; Fri, 13 May 2005 04:39:04 +0000 (GMT) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 44F5943D55 for ; Fri, 13 May 2005 04:39:04 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from [127.0.0.1] ([168.103.85.57]) (authenticated bits=0) by pooker.samsco.org (8.13.3/8.13.3) with ESMTP id j4D4hM4f051256; Thu, 12 May 2005 22:43:23 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <42842F46.9040608@samsco.org> Date: Thu, 12 May 2005 22:38:30 -0600 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.5) Gecko/20050218 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Michael Hopkins References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-2.8 required=3.8 tests=ALL_TRUSTED autolearn=failed version=3.0.2 X-Spam-Checker-Version: SpamAssassin 3.0.2 (2004-11-16) on pooker.samsco.org cc: "freebsd-amd64@freebsd.org" Subject: Re: Actual benefits of amd64 over i386 X-BeenThere: freebsd-amd64@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Porting FreeBSD to the AMD64 platform List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 May 2005 04:39:05 -0000 Michael Hopkins wrote: > > Hi all > > I have been suffering quite a bit of frustration recently with many ports > that I need being 'i386 only' and no straightforward fixes. Maybe amd64 > could be described as 'tier 1.5' ;o) > > Can I ask for honest opinions here on what speed (or other?) benefits I > should get by running amd64 over i386? I will never be using more than > about 1 G of memory on this particular machine so memory limit is not an > issue. Maybe I should just rebuild the machine as i386? > > It's an Athlon64 3400+ on a Gigabyte motherboard - used mainly for > cross-compiling to Linux and mingw32, NFS file sharing, some X11 over the > network with my local Mac OS X machine as X server and using my own C/C++ > maths code (which must run as fast as possible). > > TIA > > Michael > The theoretical advantage of amd64 is that there are more registers and wider registers. This means that more effecient code can be generated by the compiler, especially math code. There is also the benefit of being able to address more than 4GB of RAM without requiring partial tricks like PAE. However, 64-bit addresses and pointers means that the cache gets consumed less efficiently. So, it's a tradeoff, and much of it probably relies on how well the compiler generates code. Of course, the large memory handling is a definite win, but if your application doesn't need that then the benefits are less clear. Still, the Athlon64 and Opteron CPUs are quite speedy. Scott