Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751414AbVJKIGn (ORCPT ); Tue, 11 Oct 2005 04:06:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751417AbVJKIGn (ORCPT ); Tue, 11 Oct 2005 04:06:43 -0400 Received: from mx1.suse.de ([195.135.220.2]:1413 "EHLO mx1.suse.de") by vger.kernel.org with ESMTP id S1751414AbVJKIGm (ORCPT ); Tue, 11 Oct 2005 04:06:42 -0400 To: "Vladimir B. Savkin" Cc: john stultz , lkml , Andrew Morton , discuss@x86-64.org Subject: Re: [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs References: <1127157404.3455.209.camel@cog.beaverton.ibm.com> <20051007122624.GA23606@tentacle.sectorb.msk.ru> <200510071431.47245.ak@suse.de> <20051008101153.GA1541@tentacle.sectorb.msk.ru> <1128967404.8195.419.camel@cog.beaverton.ibm.com> <20051010181216.GA21548@tentacle.sectorb.msk.ru> <434AB0BE.3080206@mysql.com> <20051011073532.GA29254@tentacle.sectorb.msk.ru> From: Andi Kleen Date: 11 Oct 2005 10:06:33 +0200 In-Reply-To: <20051011073532.GA29254@tentacle.sectorb.msk.ru> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 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 Content-Length: 1267 Lines: 26 "Vladimir B. Savkin" writes: > On Mon, Oct 10, 2005 at 08:19:42PM +0200, Jonas Oreland wrote: > > Hi, > > > > check http://bugzilla.kernel.org/show_bug.cgi?id=5283 > > Excuse me for possibly dumb question, but is it safe to leave TSCs > unsynchronized when using other time source? > How will other subsystems e.g. traffic queueing disciplines react? They might see hickups, but normally they all have relatively benign failure modes so I wouldn't worry too much. If you use it on a Opteron with frequency scaling and multiple sockets it would be safer to patch them to use do_gettimeofday() or better monotonic_clock(), because the differences can be very large there (CPUs running with completely different frequencies). Drawback would be that it would be slower. On systems without frequency scaling you would likely only see problems if at all after a long uptime. For some subsystems it is ok, e.g. the scheduler which also uses TSCs especially deals with unsynchronized clocks. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/