From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263407AbTHFOgo (ORCPT ); Wed, 6 Aug 2003 10:36:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263738AbTHFOgo (ORCPT ); Wed, 6 Aug 2003 10:36:44 -0400 Received: from delta.ds2.pg.gda.pl ([213.192.72.1]:33765 "EHLO delta.ds2.pg.gda.pl") by vger.kernel.org with ESMTP id S263407AbTHFOgn (ORCPT ); Wed, 6 Aug 2003 10:36:43 -0400 Date: Wed, 6 Aug 2003 16:33:14 +0200 (MET DST) From: "Maciej W. Rozycki" To: Pavel Machek cc: Alan Cox , Adrian Bunk , lkml Subject: Re: TSCs are a no-no on i386 In-Reply-To: <20030806110855.GA583@elf.ucw.cz> Message-ID: Organization: Technical University of Gdansk MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 6 Aug 2003, Pavel Machek wrote: > > > Note that this can also allow Step-A 486's to correctly run multi-thread > > > applications since cmpxchg has a wrong opcode on this early CPU. > > > > > > Don't use this to enable multi-threading on an SMP machine, the lock > > > atomicity can't be guaranted! > > > > That is of course the other problem with this approach - you can't > > really get the intended results without some extremely heavyweight code > > (using an IPI to halt all CPU's, doing the access and then resuming > > them) > > Hopefully there are not too many SMP-486 machines out there ;-). Step-A i486 processors are supposedly very rare and they were the earliest ones (predating the DX suffix), so they were probably never used for SMP systems. And I think the i82489DX APIC was introduced a bit later anyway -- we don't support non-APIC SMP implementations. BTW, the step-A i486 reused opcodes of the famous i386's ibts and xbts instructions. Once the chips were out, Intel discovered there is actually some software out there expecting ibts/xbts semantics with these opcodes, so the encoding of cmpxchg was quickly changed. ;-) -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available +