From owner-freebsd-arch@FreeBSD.ORG Thu Apr 1 10:12:17 2004 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 6173316A4CF for ; Thu, 1 Apr 2004 10:12:17 -0800 (PST) Received: from mail5.speakeasy.net (mail5.speakeasy.net [216.254.0.205]) by mx1.FreeBSD.org (Postfix) with ESMTP id 33CEC43D41 for ; Thu, 1 Apr 2004 10:12:17 -0800 (PST) (envelope-from jhb@FreeBSD.org) Received: (qmail 4616 invoked from network); 1 Apr 2004 18:12:16 -0000 Received: from dsl027-160-063.atl1.dsl.speakeasy.net (HELO server.baldwin.cx) ([216.27.160.63]) (envelope-sender ) encrypted SMTP for ; 1 Apr 2004 18:12:16 -0000 Received: from 10.50.40.205 (gw1.twc.weather.com [216.133.140.1]) by server.baldwin.cx (8.12.10/8.12.10) with ESMTP id i31IC2DF054115; Thu, 1 Apr 2004 13:12:02 -0500 (EST) (envelope-from jhb@FreeBSD.org) From: John Baldwin To: Bruce Evans Date: Thu, 1 Apr 2004 11:23:35 -0500 User-Agent: KMail/1.6 References: <20040328094048.GA40406@phantom.cris.net> <200403311105.19088.john@baldwin.cx> <20040401145536.A5418@gamplex.bde.org> In-Reply-To: <20040401145536.A5418@gamplex.bde.org> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message-Id: <200404011123.36337.jhb@FreeBSD.org> X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on server.baldwin.cx cc: arch@freebsd.org cc: Alexey Zelkin cc: Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= Subject: Re: CFD: XMLification of NOTES X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 01 Apr 2004 18:12:17 -0000 On Thursday 01 April 2004 12:11 am, Bruce Evans wrote: > On Wed, 31 Mar 2004, John Baldwin wrote: > > On Tuesday 30 March 2004 06:54 pm, Dag-Erling Sm=F8rgrav wrote: > > > CPU_I386 should not conflict with SMP, but a kernel build with both > > > will be very slow. > > > > No, it does conflict. There's no cmpxchg on i386 and no one has had the > > desire or time to emulate one for 386 machines. Doing so would be a > > waste in my opinion as well. > > des only claimed that it "should not". > > Emulating cmpxchg might make a kernel built with both slow, but the > current CPU_I386 only adds a tiny amount of slowness. It just doesn't > work on multi-CPU systems if multiple CPUs are actually used. > > Does it actually conflict in practice (except for the forced #error) > if the hardware is UP? jhb's APIC changes made configuring with SMP > not require APIC, so SMP kernels work on UP systems. Configuring with > I386_CPU shouldn't affect this, but it does because of the forced #error > at compile time. > > Bruce Hmm. Well, if the hardware is UP the kernel still does 'cmpxchg'=20 instructions, so you'd still have to emulate cmpxchg for the kernel. There= 's=20 another problem in that I think Peter changed the pmap to make using invltl= b=20 in place of invlpg be a compile time decision rather than a runtime decisio= n. If someone wants to write an in-kernel cmpxchg emulator then I wouldn't min= d=20 having I386_CPU just turn on the extra runtime checks for invltlb vs. invlp= g. =2D-=20 John Baldwin <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" =3D http://www.FreeBSD.org