[libvirt] [virt-devel] RFC: Modelling timers / clocks & tick policies in libvirt

[Zachary Amsden]

On 03/05/2010 07:05 AM, Daniel P. Berrange wrote:
> On Fri, Mar 05, 2010 at 06:50:47AM -1000, Zachary Amsden wrote:
>    
>> On 03/05/2010 04:27 AM, Daniel P. Berrange wrote:
>>      
>>>   * HPET
>>>      Multiple timers with periodic interrupts
>>>      Can replace PIT/RTC timers
>>>
>>> They all generally suck in real hardware, and this gets worse in virtual
>>> machines.
>>> Many different approaches to making them suck less in VMWare, Xen&   KVM,
>>> but there
>>> are some reasonably common concepts....
>>>
>>>        
>> HPET doesn't suck.
>>      
> The VMWare timekeeping docs mentions that it has timeout race conditions,
> poorly defined spec for timer granularity, drift&  speed of access,&  bad
> implementations in the real world which I read as 'sucks' ;-)
>    

Which can also be read as nearly perfectly virtualizable due to extreme 
variations in tolerance and hardened guest code ;)