Re: Make QEmu HPET disabled by default for KVM?

[Dor Laor <dlaor@redhat.com>]

On 03/14/2010 09:10 AM, Gleb Natapov wrote:
> On Sun, Mar 14, 2010 at 09:05:50AM +0200, Avi Kivity wrote:
>> On 03/11/2010 09:08 PM, Marcelo Tosatti wrote:
>>>
>>>>
>>>>> I have kept --no-hpet in my setup for
>>>>> months...
>>>> Any details about the problems?  HPET is important to some guests.
>>> As Gleb mentioned in the other thread, reinjection will introduce
>>> another set of problems.
>>>
>>> Ideally all this timer related problems should be fixed by correlating
>>> timer interrupts and time source reads.
>>
>> This still needs reinjection (or slewing of the timer frequency).
>> Correlation doesn't fix drift.
>>
> But only when all time sources are synchronised and correlated with
> interrupts we can slew time frequency without guest noticing (and only
> if guest disables NTP)

In the mean time we should definitely disable hpet by default.
Besides this we need to fully virtualize the tsc, fix win7 64bit rtc 
time drift and some pvclock potential issues. Before we add new timer, 
better fix existing ones.

What about creating a pv time keeping device that will be aware of lost 
ticks and host wall clock time? It's similar to hyper-v enlightenment 
virt timers.

>
>>> Since one already has to use special timer parameters (-rtc-td-hack,
>>> -no-kvm-pit-reinjection), using -no-hpet for problematic Linux
>>> guests seems fine?
>>
>> Depends on how common the problematic ones are.  If they're common,
>> better to have a generic fix.
>>
>> --
>> error compiling committee.c: too many arguments to function
>
> --
> 			Gleb.
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