Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753245Ab0DSSfz (ORCPT ); Mon, 19 Apr 2010 14:35:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42124 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751526Ab0DSSfx (ORCPT ); Mon, 19 Apr 2010 14:35:53 -0400 Message-ID: <4BCCA281.6040509@redhat.com> Date: Mon, 19 Apr 2010 08:35:45 -1000 From: Zachary Amsden User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3 MIME-Version: 1.0 To: Avi Kivity CC: Peter Zijlstra , Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock 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> <1271674273.1674.777.camel@laptop> <4BCC3654.2090600@redhat.com> In-Reply-To: <4BCC3654.2090600@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1097 Lines: 30 On 04/19/2010 12:54 AM, Avi Kivity wrote: > On 04/19/2010 01:51 PM, Peter Zijlstra wrote: >> >>>> 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. > > Worrying. By the time we detect this the guest may already have > gotten confused by clocks going backwards. Upstream, we are marking the TSC unstable preemptively when hardware which will eventually sync test is detected, so this should be fine. Zach -- 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/