Re: [Qemu-devel] Re: [RFC: 0/2] patch for QEMU HPET periodic timer emulation to alleviate time drift

[Avi Kivity <avi@redhat.com>]

On 02/07/2011 03:11 PM, Anthony Liguori wrote:
> On 02/07/2011 06:34 AM, Avi Kivity wrote:
>> On 02/04/2011 10:56 AM, Jan Kiszka wrote:
>>> >
>>> >  This should be a rare event.  If you are missing 50% of your
>>> >  notifications, not amount of gradual catchup is going to help you 
>>> out.
>>>
>>> But that's the only thing this patch is after: lost ticks at QEMU 
>>> level.
>>
>> Most lost ticks will happen at the vcpu level.  The iothread has low 
>> utilization and will therefore be scheduled promptly, whereas the 
>> vcpu thread may have high utilization and will thus be preempted.  
>> When it is preempted for longer than the timer tick, we will see 
>> vcpu-level coalescing.  All it takes is 2:1 overcommit to see time go 
>> half as fast; I don't think you'll ever see that on bare metal.
>
> But that's not to say that doing something about lost ticks in QEMU 
> isn't still useful.
>

If it doesn't solve the majority of the problems it isn't very useful 
IMO.  It's a good first step, but not sufficient for real world use with 
overcommit.

-- 
error compiling committee.c: too many arguments to function