Re: [PATCH 0/6] In kernel PIT patch

[Dor Laor <dor.laor@gmail.com>]

On Wed, 2008-03-05 at 17:05 -0600, Anthony Liguori wrote:
> Dor Laor wrote:
> > On Wed, 2008-03-05 at 19:30 +0200, Avi Kivity wrote:
> >   
> >>
> >> Playing a movie is better than any benchmark; it reflects actual user 
> >> experience in a real and important use case.  Benchmarks are substitutes 
> >> for real use cases, not the goal of the optimization.
> >>
> >>     
> >
> > I forgot to mention that the benchmark is measuring time drift in the
> > guest. Playing a movie in winxp changes the guest clock frequency from
> > 100HZ to 1000HZ, thus causing a 250HZ host to coalesce pit irqs.
> >
> > So good pic & pit combination can handle guest multimedia without drifts
> > while insufficient implementation just can't.
> >   
> 
> I'll try out these patches in the next day or so.  Is the expectation 
> that Standard HAL + in-kernel APIC/PIT will have smoother playback than 
> ACPI HAL w/o in-kernel APIC/PIT?  I presume that the ACPI HAL is 
> unaffected by in-kernel PIT?
> 

Standard HAL + userspace pic + -tdf option should give no guest time
drift (actually sometimes massive correction of irq injection do the
opposite, also since time drifts without -dtf it might look better but
the movie does not runs in real time).
Standard HAL + in-kernel pit patch + in-kernel irqchip should not drift.
All other combinations should drift (sometimes you need to overload the
cpu to see the drift).

As for ACPI hal, the in-kernel apic doesn't drift, it also enable having
flex priority or Avi's tpr optimization that boost overall performance.

ACPI HAL should not be affected by the in-kernel pit.

> Regards,
> 
> Anthony Liguori
> 
> 


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/