On Thu, Mar 11, 2010 at 10:46:06AM +0200, Avi Kivity wrote: > On 03/11/2010 10:42 AM, Gleb Natapov wrote: > >On Thu, Mar 11, 2010 at 04:38:48PM +0800, Sheng Yang wrote: > >>On Thursday 11 March 2010 16:31:57 Gleb Natapov wrote: > >>>On Thu, Mar 11, 2010 at 10:28:12AM +0200, Avi Kivity wrote: > >>>>On 03/11/2010 10:23 AM, Sheng Yang wrote: > >>>>>>>I have kept --no-hpet in my setup for > >>>>>>>months... > >>>>>>Any details about the problems? HPET is important to some guests. > >>>>>Seems like HPET reaction is too slow to satisfy some guests(for it would > >>>>>replace PIT). > >>>>> > >>>>>Here is the thread last time. > >>>>> > >>>>>http://thread.gmane.org/gmane.comp.emulators.kvm.devel/44899 > >>>>Thanks. We can address this in three ways: first, adjust the guest > >>>>not to do timing related tests when virtualized (since no matter > >>>>what we do, the tests may fail). Second, I think we should > >>>>implement userspace ack notifiers (similar to tpr access notifiers > >>>>already present). Third, we can implement a kernel hpet, which, > >>>>after we solve the zillion bug it introduces, will also give a nice > >>>>performance improvement for hpet intensive workloads. > >>>Second will not solve the problem. Presence of ack notifiers will not > >>>make HPET interrupt arrive faster. > >>The slow may also due to lost tick. And with the lost tick, hpet is still > >>unusable... > >> > >If the problem it due to lost ticks reinjection may solve it, but only partially. > >What if IO thread haven't run even once during the time vcpu did clock > >source check? IIRC sometimes we trigger this even with in kernel PIT. > > That is true. Reinjection can correct problems in the long term, > but may fail in the short term. 10 ticks is easily short term in a > heavily loaded system. > > How does it happen with kernel PIT? I could understand it if we had > a work item doing the injection, but everything happens either from > hrtimer context or vcpu context. > Do we kick vcpu out of guest mode when hrtimer triggers? I don't see us doing it in __kvm_timer_fn(). -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
