Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754213Ab0DSKvT (ORCPT ); Mon, 19 Apr 2010 06:51:19 -0400 Received: from casper.infradead.org ([85.118.1.10]:60748 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753980Ab0DSKvR (ORCPT ); Mon, 19 Apr 2010 06:51:17 -0400 Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock From: Peter Zijlstra To: Avi Kivity Cc: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden In-Reply-To: <4BCC3520.6090305@redhat.com> References: <1271356648-5108-1-git-send-email-glommer@redhat.com> <1271356648-5108-2-git-send-email-glommer@redhat.com> <4BCA026D.3070309@redhat.com> <1271673975.1674.763.camel@laptop> <4BCC3520.6090305@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 19 Apr 2010 12:51:13 +0200 Message-ID: <1271674273.1674.777.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1229 Lines: 32 On Mon, 2010-04-19 at 13:49 +0300, Avi Kivity wrote: > On 04/19/2010 01:46 PM, Peter Zijlstra wrote: > > On Sat, 2010-04-17 at 21:48 +0300, Avi Kivity wrote: > > > >>> After this patch is applied, I don't see a single warp in time during 5 days > >>> of execution, in any of the machines I saw them before. > >>> > >>> > >>> > >> Please define a cpuid bit that makes this optional. When we eventually > >> enable it in the future, it will allow a wider range of guests to enjoy it. > >> > > Right, so on x86 we have: > > > > X86_FEATURE_CONSTANT_TSC, which only states that TSC is frequency > > independent, not that it doesn't stop in C states and similar fun stuff. > > > > X86_FEATURE_TSC_RELIABLE, which IIRC should indicate the TSC is constant > > and synced between cores. > > > > > > Sockets and boards too? (IOW, how reliable is TSC_RELIABLE)? Not sure, IIRC we clear that when the TSC sync test fails, eg when we mark the tsc clocksource unusable. -- 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/