From: Jeremy Fitzhardinge Subject: Re: [Xen-devel] Re: [PATCH] x86/pvclock-xen: zero last_value on resume Date: Wed, 27 Oct 2010 11:53:18 -0700 Message-ID: <4CC8751E.40306@goop.org> References: <4CC708DE.1070000@goop.org> <1288115334.3530.7.camel@mothafucka.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1288115334.3530.7.camel@mothafucka.localdomain> Sender: kvm-owner@vger.kernel.org To: Glauber Costa Cc: "Xen-devel@lists.xensource.com" , kvm-devel , Eelco Dolstra , the arch/x86 maintainers , Linux Kernel Mailing List , Linux Virtualization , Olivier Hanesse , Avi Kivity , "H. Peter Anvin" List-Id: xen-devel@lists.xenproject.org On 10/26/2010 10:48 AM, Glauber Costa wrote: > On Tue, 2010-10-26 at 09:59 -0700, Jeremy Fitzhardinge wrote: >> If the guest domain has been suspend/resumed or migrated, then the >> system clock backing the pvclock clocksource may revert to a smaller >> value (ie, can be non-monotonic across the migration/save-restore). >> Make sure we zero last_value in that case so that the domain >> continues to see clock updates. >> >> [ I don't know if kvm needs an analogous fix or not. ] > After migration, save/restore, etc, we issue an ioctl where we tell > the host the last clock value. That (in theory) guarantees monotonicity. > > I am not opposed to this patch in any way, however. Thanks. HPA, do you want to take this, or shall I send it on? Thanks, J