From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: #599161: Xen debug patch for the "clock shifts by 50 minutes" bug. Date: Thu, 08 Nov 2012 12:54:17 +0000 Message-ID: References: <1352375011.12977.95.camel@hastur.hellion.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1352375011.12977.95.camel@hastur.hellion.org.uk> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: "Philippe.Simonet@swisscom.com" , "599161@bugs.debian.org" <599161@bugs.debian.org>, "mrsanna1@gmail.com" , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 08/11/2012 11:43, "Ian Campbell" wrote: >>> I'll leave this to Keir (who wrote the debugging patch) to answer but it >>> looks to me like it should be useful! >> >> I'm scratching my head. plt_wrap is earlier than plt_now, which should be >> impossible. > > impossible due to guarantees made by the h/w or by construction in Xen. That's a question, right? By construction in Xen. > There appears to be a certain amount of hardware-specificness to the > issue -- so I'm wondering if maybe there are some platforms whose tsc is > not as monotonically increasing as it needs to be... plt_* timestamps are not derived from TSC at all. >> plt_stamp64 oddly has low 32 bits identical to new_stamp. That >> seems very very improbable! > > Does this code run on all cpus or just one? Is it always the same one? Always cpu0. -- Keir