From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: softtsc for PV guests Date: Fri, 21 Aug 2009 16:59:58 -0700 Message-ID: <4A8F34FE.6040602@goop.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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: Dan Magenheimer Cc: "Xen-Devel (E-mail)" List-Id: xen-devel@lists.xenproject.org On 08/21/09 16:31, Dan Magenheimer wrote: > Enabling CR4_TSD only traps ring>0 rdtscs. Trapping guest kernel > rdtsc's is ultimately necessary because the Linux kernel does NOT > adequately handle all the possible changes in TSC characteristics > that can occur if Xen moves an already booted guest from one > physical machine to another (or even from one set of pcpus > to another on certain physical machines). I recognize this > is very ugly, but it may be the only way to guarantee > correctness 100% of the time. PV guests already correct for that by using the data Xen provides; they don't require Xen to do any correction or synthesis of tsc values. > The system is definitely not dead, but dom0 is busy looping or > something. I can probably isolate the code, but the xen > changes seem small enough that it's hard to believe they > could cause this kind of problem. > '0' on the Xen console will tell you where its spinning. Oh, is it dom0 or domU? J