From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Magenheimer Subject: RE: [Xen-devel] Domain-Virtual time Date: Thu, 25 Feb 2010 12:36:00 -0800 (PST) Message-ID: References: <5c3550fe1002250803q21decea2j101c53fe390b856c@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <5c3550fe1002250803q21decea2j101c53fe390b856c@mail.gmail.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-users-bounces@lists.xensource.com Errors-To: xen-users-bounces@lists.xensource.com To: Priya , xen-devel@lists.xensource.com, xen-users@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Should be "true" system time, i.e. should be very close to what you see on a "wallclock" (clock on the wall). HVM's are sadly very widely varied in the parameters needed to minimize time drift. In general in the past, timer_mode=3D0 (or timer_mode unspecified) would be best for 32-bit Linux domains, timer_mode=3D1 would be best for Windows domains, and timer_mode=3D2 would be best for 64-bit Linux domains. However, for best results on Linux, this must be combined with kernel boot parameters that properly select a clock -- and on some Linux kernel versions, the parameters needed are different between 32-bit and 64-bit versions of the same kernel version. It is up to providers of HVM templates (aka "appliances") to choose parameters wisely. Also, you haven't specified your Xen version, but I believe Xen 4.0 switches the timer_mode default from 0 to 1 so, sadly, clock behavior may change when moving an unchanged HVM domain from pre-4.0 to 4.0. So for best results you should run ntpd in any Linux HVM domain (and I don't know what you do in Windows). But even ntpd may be inadequate to avoid drift if poor parameters are chosen. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D From: Priya [mailto:pbhat@acis.ufl.edu]=20 Sent: Thursday, February 25, 2010 9:04 AM To: xen-devel@lists.xensource.com; xen-users@lists.xensource.com Subject: [Xen-devel] Domain-Virtual time Sorry for multiple emails. I sent the last one from the wrong address. Can anyone please tell me if the value returned by a time querying instruct= ion like gettimeofday() on a Xen (Linux) HVM is the true (System) time or t= he Domain-virtual time? PS: Domain virtual time is defined as the time that progresses at the same = pace as cycle counter, but only while a domain is executing. It stops while= the domain is de-scheduled where as System time accurately reflects the pa= ssage of real time. I am facing issues because my HVMs show a time drift.=20 Thanks