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



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 ;)


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