Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758819Ab0FPN6u (ORCPT ); Wed, 16 Jun 2010 09:58:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39865 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756061Ab0FPN6t (ORCPT ); Wed, 16 Jun 2010 09:58:49 -0400 Date: Wed, 16 Jun 2010 10:58:45 -0300 From: Glauber Costa To: Jason Wang Cc: Zachary Amsden , avi@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 11/17] Fix a possible backwards warp of kvmclock Message-ID: <20100616135845.GM19104@mothafucka.localdomain> References: <1276587259-32319-1-git-send-email-zamsden@redhat.com> <1276587259-32319-12-git-send-email-zamsden@redhat.com> <4C18872E.4030105@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C18872E.4030105@redhat.com> X-ChuckNorris: True User-Agent: Jack Bauer Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1007 Lines: 19 On Wed, Jun 16, 2010 at 04:11:26PM +0800, Jason Wang wrote: > Zachary Amsden wrote: > > Kernel time, which advances in discrete steps may progress much slower > > than TSC. As a result, when kvmclock is adjusted to a new base, the > > apparent time to the guest, which runs at a much higher, nsec scaled > > rate based on the current TSC, may have already been observed to have > > a larger value (kernel_ns + scaled tsc) than the value to which we are > > setting it (kernel_ns + 0). > > > This is one issue of kvmclock which tries to supply a clocksource whose > precision may even higher than host. What if we export to the guest the current clock resolution, and when doing guest reads, simply chop whatever value we got to the lowest acceptable value? -- 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/