Re: Make QEmu HPET disabled by default for KVM?

Avi Kivity
2010-03-11T08:36:11Z

On 03/11/2010 10:31 AM, 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.
>

But it will allow us to compensate for interrupts being coalesced, which
may be the root of the problem.

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