Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756744AbXLSQzs (ORCPT ); Wed, 19 Dec 2007 11:55:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754013AbXLSQzi (ORCPT ); Wed, 19 Dec 2007 11:55:38 -0500 Received: from mis011-1.exch011.intermedia.net ([64.78.21.128]:44704 "EHLO mis011-1.exch011.intermedia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754283AbXLSQzh (ORCPT ); Wed, 19 Dec 2007 11:55:37 -0500 From: Amit Shah Organization: Qumranet Technologies To: kvm-devel@lists.sourceforge.net Subject: Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup Date: Wed, 19 Dec 2007 22:25:53 +0530 User-Agent: KMail/1.9.6 Cc: "Glauber de Oliveira Costa" , "Avi Kivity" , linux-kernel , Avi Kivity , Gerd Hoffmann References: <47680173.6060606@qumranet.com> <47692A47.4040803@argo.co.il> <5d6222a80712190732h515a63e6y49c64c0f572f044@mail.gmail.com> In-Reply-To: <5d6222a80712190732h515a63e6y49c64c0f572f044@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200712192225.53748.amit.shah@qumranet.com> X-OriginalArrivalTime: 19 Dec 2007 16:55:36.0136 (UTC) FILETIME=[F9DC7480:01C8425F] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1668 Lines: 40 On Wednesday 19 December 2007 21:02:06 Glauber de Oliveira Costa wrote: > On Dec 19, 2007 12:27 PM, Avi Kivity wrote: > > Ingo Molnar wrote: > > > * Avi Kivity wrote: > > >> Avi Kivity wrote: > > >>> Testing shows wrmsr and rdtsc function normally. > > >>> > > >>> I'll try pinning the vcpus to cpus and see if that helps. > > >> > > >> It does. > > > > > > do we let the guest read the physical CPU's TSC? That would be trouble. > > > > vmx (and svm) allow us to add an offset to the physical tsc. We set it > > on startup to -tsc (so that an rdtsc on boot would return 0), and > > massage it on vcpu migration so that guest rdtsc is monotonic. > > > > The net effect is that tsc on a vcpu can experience large forward jumps > > and changes in rate, but no negative jumps. > > Changes in rate does not sound good. It's possibly what's screwing up > my paravirt clock implementation in smp. Do you mean in the case of VM migration, or just starting them on a single host? > Since the host updates guest time prior to putting vcpu to run, two > vcpus that start running at different times will have different system > values. > > Now if the vcpu that started running later probes the time first, > we'll se the time going backwards. A constant tsc rate is the only way > around > my limited mind sees around the problem (besides, obviously, _not_ > making the system time per-vcpu). -- 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/