[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] timekeepeing in XEN - request fo comments
Hi Pasi -- The timekeeping problems I am referring to are only(?) for hvm guests. HVM guests with different OS's and different versions of a Linux kernel (32-bit vs 64-bit, even kernel updates between EL5uX and EL5uX+1) behave differently when ticks are delivered at imperfect intervals (which happens frequently for Xen and other hypervisors). Xen distros and "virtual appliance" distributors may specify certain settings of timer_mode and certain kernel parameters (e.g. "clock=pit") to ensure time is kept as accurately as possible. There is no "one size fits all" solution unfortunately. For PV guests, note that there have been patches to dom0 (2.6.18-xen) that improve timekeeping in dom0 and this may affect pv guests with independent_wallclock==0. I don't know if the patches have been applied to pv_ops dom0, or if they are even necessary. In fact, I don't know if there is a concept of independent_wallclock in pv_ops. Dan > -----Original Message----- > From: Pasi Kärkkäinen [mailto:pasik@xxxxxx] > Sent: Monday, November 09, 2009 11:50 AM > To: Dan Magenheimer > Cc: Bartosz Lis; xen-devel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [Xen-devel] timekeepeing in XEN - request fo comments > > > On Mon, Nov 09, 2009 at 08:50:52AM -0800, Dan Magenheimer wrote: > > What kernels are running in your domUs? Are they > > also (all) 2.6.31.5? If your domU's are older kernels > > (e.g. SLES10 or older, RHEL5 or older) there are > > many issues that cannot be entirely solved by > > Xen or dom0. > > > > Could you tell more about these timekeeping problems with > SLES10/RHEL5 PV kernels? > > -- Pasi > > > > -----Original Message----- > > > From: Bartosz Lis [mailto:bartoszl@xxxxxxxxxxxxx] > > > Sent: Monday, November 09, 2009 5:21 AM > > > To: xen-devel@xxxxxxxxxxxxxxxxxxx > > > Subject: [Xen-devel] timekeepeing in XEN - request fo comments > > > > > > > > > Dear developers, > > > > > > I have some issues with time synchronization among dom0 and > > > domUs. In my case > > > helped reconfiguring kernel with HZ=1000 for dom0 and HZ=100 > > > for domUs and > > > running ntpd also on domUs. I think, running ntpd on domU is > > > not a good idea, > > > but it works acceptably good as a workaround for my > > > configuration: XEN 3.4.1 + > > > kernel 3.6.31.5 with pv_ops (taken from git last week). When > > > I don't run ntpd > > > on domU clock slowly drifts. I have choosen xen clocksource > > > in both dom0 and > > > domU. > > > > > > I'm not the only one to have time synchronization issues. > > > Please write some > > > document specifying how time synchronization between dom0 and > > > domU should be > > > achieved. I have a number of special questions, but probably > > > there are more > > > questions that should be aswered: > > > > > > 1. What is the mechanics behind the clocksource named xen? > > > How does it depend > > > on phisical time sources available on different platforms? > > > > > > 2. How gets domU's clock initialized when domU boots? (I > > > observe that just > > > after domU has started its clock differs from dom0. The > > > difference is about > > > 10s.) > > > > > > 3. What are the consequences of not selecting xen clocksource > > > (by selecting > > > one of hpet, acpi_pm, etc.) for dom0 and for domU? > > > > > > 4. What are the best practices to achieve clock synchronization? > > > > > > 5. What has changed recently in timekeeping? What is going to > > > change? Are > > > there any improvements/bugfixes added to redhat or suse > > > kernels? Are these > > > bugfixes planned to be added upstream? > > > > > > Thank you in advance, > > > > > > -- > > > Bartosz Lis @ Inst. of Information Technology, Technical > > > Univ. of Lodz, Poland > > > bartoszl @ ics.p.lodz.pl > > > > > > _______________________________________________ > > > Xen-devel mailing list > > > Xen-devel@xxxxxxxxxxxxxxxxxxx > > > http://lists.xensource.com/xen-devel > > > > > > > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@xxxxxxxxxxxxxxxxxxx > > http://lists.xensource.com/xen-devel > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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