From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261907AbVACWZb (ORCPT ); Mon, 3 Jan 2005 17:25:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261912AbVACWXN (ORCPT ); Mon, 3 Jan 2005 17:23:13 -0500 Received: from holomorphy.com ([207.189.100.168]:2719 "EHLO holomorphy.com") by vger.kernel.org with ESMTP id S261906AbVACWPW (ORCPT ); Mon, 3 Jan 2005 17:15:22 -0500 Date: Mon, 3 Jan 2005 14:15:16 -0800 From: William Lee Irwin III To: Colin Coe Cc: linux-kernel@vger.kernel.org Subject: Re: Max CPUs on x86_64 under 2.6.x Message-ID: <20050103221516.GV29332@holomorphy.com> References: <44438.202.154.120.74.1104760841.squirrel@www.coesta.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44438.202.154.120.74.1104760841.squirrel@www.coesta.com> Organization: The Domain of Holomorphy User-Agent: Mutt/1.5.6+20040722i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 03, 2005 at 10:00:41PM +0800, Colin Coe wrote: > Why is the number of CPUs on the x86_64 architecture only 8 but under i386 > it is 255? > I've searched the list archives and Google but can't find an answer. i386 machines have had interrupt controllers and "large scale" systems (to the extent that 32-bit machines can be so) developed for some time. x86-64 machines are newer, and it is the maintainer's preference to start with a fresh codebase for the APIC. So what you see is not a reflection of x86-64's capabilities, but rather, of the newness of the architecture and the codebase's desire to be "legacy-free" in manners that don't pose the threat of causing immediate problems. It is not now limiting the capabilities of x86-64 machines because x86-64 machines of 64 cpus or larger have yet to be produced. For the record, I'm unaware of SSI i386 machines larger than 64 processors. 255 represents nothing more than a theoretical limit of hardware capabilities, and no i386 machine larger than 64 processors has ever been constructed to the best of my knowledge. -- wli