From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LRcKT-0003O3-Oz for qemu-devel@nongnu.org; Mon, 26 Jan 2009 20:01:25 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LRcKS-0003LU-LI for qemu-devel@nongnu.org; Mon, 26 Jan 2009 20:01:25 -0500 Received: from [199.232.76.173] (port=50330 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LRcKS-0003L5-Dg for qemu-devel@nongnu.org; Mon, 26 Jan 2009 20:01:24 -0500 Received: from mx20.gnu.org ([199.232.41.8]:62740) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LRcKS-0008WM-0d for qemu-devel@nongnu.org; Mon, 26 Jan 2009 20:01:24 -0500 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LRcIW-0008KJ-7g for qemu-devel@nongnu.org; Mon, 26 Jan 2009 19:59:24 -0500 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH] Enabled building of x86_64 code on Mac OS X Date: Tue, 27 Jan 2009 00:59:20 +0000 References: <1232826287-18542-1-git-send-email-agraf@suse.de> <200901270034.04844.paul@codesourcery.com> <20090127004232.GE9296@shareable.org> In-Reply-To: <20090127004232.GE9296@shareable.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200901270059.21958.paul@codesourcery.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Anthony Liguori On Tuesday 27 January 2009, Jamie Lokier wrote: > Paul Brook wrote: > > > Out of curiousity, what are the benefits of using 64-bit apps in OS X? > > > > My guess is that same as most other x86 targets: The i386 legacy > > mode is crippled by lack of registers, modern x86 hardware has a big > > fat wide memory bus, and noone's bothered implementing an ILP32 > > 64-bit API[1], so 64-bit apps give measurably better overall > > performance. > > Except they use more memory and memory bandwidth (arguably filling > nearly half of it with zeros most of the time :-) so worse overall > performance in some cases. I did say overall performance. My experience with AMD hardware is that you generally get ~10% overall improvement from LP64. Intel hardware (particularly the early 64-bit cores) less so, but it's generally still a win. I guess ILP32 long mode would probably increase that further, and avoid the odd regressions. It's an awful lot of work to implement though, especially on a target that isn't used to having lots of incompatible variants. Paul