From owner-freebsd-amd64@FreeBSD.ORG Fri May 13 19:17:07 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 5F12816A4CE for ; Fri, 13 May 2005 19:17:07 +0000 (GMT) Received: from coe.ufrj.br (roma.coe.ufrj.br [146.164.53.65]) by mx1.FreeBSD.org (Postfix) with ESMTP id 043C943D48 for ; Fri, 13 May 2005 19:17:06 +0000 (GMT) (envelope-from jonny@jonny.eng.br) Received: from localhost (localhost [127.0.0.1]) by coe.ufrj.br (Postfix) with ESMTP id A267217709; Fri, 13 May 2005 16:17:03 -0300 (BRT) Received: from coe.ufrj.br ([146.164.53.65]) by localhost (roma.coe.ufrj.br [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 71853-09; Fri, 13 May 2005 16:16:56 -0300 (BRT) Received: from [10.0.8.17] (nat.int.gov.br [200.20.196.226]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by coe.ufrj.br (Postfix) with ESMTP id 2584817707; Fri, 13 May 2005 16:16:56 -0300 (BRT) Message-ID: <4284FD37.2070009@jonny.eng.br> Date: Fri, 13 May 2005 16:17:11 -0300 From: =?ISO-8859-1?Q?Jo=E3o_Carlos_Mendes_Lu=EDs?= User-Agent: Mozilla Thunderbird 1.0+ (Windows/20050315) MIME-Version: 1.0 To: Scott Long References: <42842F46.9040608@samsco.org> In-Reply-To: <42842F46.9040608@samsco.org> X-Enigmail-Version: 0.90.2.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Virus-Scanned: amavisd-new at coe.ufrj.br cc: Michael Hopkins 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 19:17:07 -0000 Scott Long wrote: > 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. What about a 64 bit kernel, and mixed mode (32bit and 64bit) userland? Solaris does this, and it sounds efficient, from the comments I've seen in this list. This way, only those programs which would benefit from 64bit architecture would run in 64bit mode. The bad part: Most (probably all) libraries would duplicated, and the kernel and compiler should be modified to understand this "feature". If amd64 32bit executables were compatible with (maybe the same) i386 executables, even better. Note that I am not talking about i386 emulation. I am talking about native 32 bit executables in amd64 arch. Too hard to expect it in 6.0-RELEASE?