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: Wed, 07 Nov 2012 17:40:30 +0000 Message-ID: References: <1352294551.12977.61.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: <1352294551.12977.61.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 , Philippe.Simonet@swisscom.com Cc: 599161@bugs.debian.org, mrsanna1@gmail.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 07/11/2012 13:22, "Ian Campbell" wrote: >>> (XEN) XXX plt_overflow: plt_now=5ece12d34128 plt_wrap=5ece12d09306 >>> now=5ece12d16292 old_stamp=35c7c new_stamp=800366a5 >>> plt_stamp64=15b800366a5 plt_mask=ffffffff tsc=e3839fd23854 >>> tsc_stamp=e3839fcb0273 >> >> (below is the complete xm dmesg output) >> >> did that help you ? do you need more info ? > > 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. plt_stamp64 oddly has low 32 bits identical to new_stamp. That seems very very improbable! I wonder whether the overflow handling should just be removed, or made conditional on a command-line parameter, or on the 32-bit platform counter being at least somewhat likely to overflow before a softirq occurs -- it seems lots of systems are using 14MHz HPET, and that gives us a couple of minutes for the plt_overflow softirq to do its work before overflow occurs. I think we would notice that outage in other ways. :) -- Keir