From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Magenheimer Subject: RE: xen tsc problems? Date: Tue, 13 Jul 2010 08:37:41 -0700 (PDT) Message-ID: <8a9d6a6f-4727-4211-979d-5cf7ec2eade6@default> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser , Stefano Stabellini , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org > From: Keir Fraser [mailto:keir.fraser@eu.citrix.com] >=20 > On 13/07/2010 15:37, "Stefano Stabellini" > > wrote: >=20 > > Does this mean that the host has some serious tsc issues? > > Can this be a symptom of a bug in xen? > > Suggestion are welcome. >=20 > The 's' and 't' debug key handlers will be useful to get an idea of how > stable host TSCs are. >=20 > -- Keir Also you can try max_cstate=3D0 as a Xen boot parameter to rule out power management screwing up the tsc. > > Does this mean that the host has some serious tsc issues? Probably. But the default tsc_mode (0) is intended to hide all such issues. Could you check the 's' debug-key output to ensure your guest is actually running with tsc_mode=3D0? > > Can this be a symptom of a bug in xen? Well, if the guest has problems with the default tsc_mode (0), which does complete tsc emulation, I suppose it could be a bug in Xen. In particular, I wonder if the code that recovers from deep C-states (and writes to the TSC) is broken. IIRC, there was some changesets in that area recently. If the problem goes away with max_cstate=3D0, that would be a good place to start. Dan