Hi! Can anybody explain how Xen deals with time? On traditional, non-virtualized systems I run an ntpd on every system to keep the time accurate. But what to do on xenified systems? Do all the domU''s get the time from dom0 meaning it is sufficient to run an ntpd there or do I have it to setup in every domU? Thanks for your help! Kind regards, Stephan _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Am Freitag, 7. April 2006 09:10 schrieb Stephan Austermühle:> Do all the domU''s get the > time from dom0 meaning it is sufficient to run an ntpd there or do I have > it to setup in every domU?Yes. Best Regards Philipp _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Am Freitag, 7. April 2006 09:10 schrieb Stephan Austermühle:> Do all the domU''s get the > time from dom0 meaning it is sufficient to run an ntpd thereForgot to remove the part that does not apply in my last mail... domU gets the time from dom0 and is not allowed to change it -> synchronizing the time can only be done in dom0. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Fri, Apr 07, 2006 at 10:31:58AM +0200, Jan Philipp Giel wrote:> Am Freitag, 7. April 2006 09:10 schrieb Stephan Austermühle: > > Do all the domU''s get the > > time from dom0 meaning it is sufficient to run an ntpd there > > Forgot to remove the part that does not apply in my last mail... > domU gets the time from dom0 and is not allowed to change it -> synchronizing > the time can only be done in dom0.Not entirely true. You can set the domUs to have an independent clock with echo 1 > /proc/sys/xen/independent_wallclock and in fact with my systems I have had to do this to stop the domU clocks slipping out of synch dramatically (I have seen this reported on the list before but haven''t had a chance to properly investigate yet). Dominic. -- Dominic Hargreaves | http://www.larted.org.uk/~dom/ PGP key 5178E2A5 from the.earth.li (keyserver,web,email) _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Jan Philipp Giel <mail@philsown.de> writes:> Am Freitag, 7. April 2006 09:10 schrieb Stephan Austermühle: > > Do all the domU''s get the > > time from dom0 meaning it is sufficient to run an ntpd there or do I have > > it to setup in every domU? > > Yes.How does that work? I thought every domU has its own software system clock updated by regular interrupts e.g. at 100Hz or 1000Hz. This would require running ntpd to synchronize the clock to some external reference clock. Or is the gettimeofday system call modified in domU so that it communicates to dom0 to get the time, i.e. no more interrupt driven software clock in the domU? urs _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi! Urs Thuermann schrieb:> How does that work? I thought every domU has its own software system > clock updated by regular interrupts e.g. at 100Hz or 1000Hz. This > would require running ntpd to synchronize the clock to some external > reference clock. Or is the gettimeofday system call modified in domU > so that it communicates to dom0 to get the time, i.e. no more > interrupt driven software clock in the domU?Although I have not taken a look into the sources it seems that the hardware clock (RTC) is present only once (in dom0) and is reported to domU''s when they are created. Once a domU is running the guest kernel maintains its own system clock. To prevent it drifting away time synchronization is necessary in every domU. The independent wallclock switch just seems to allow a domU to write a time to the virtual RTC that is different from the real RTC. Maybe the Xen people can clarify this? Kind regards, Stephan _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users