Re: Make QEmu HPET disabled by default for KVM?

Sheng Yang
2010-03-11T08:37:17Z

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...

--
regards
Yang, Sheng