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

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

On Thu, 2008-03-06 at 14:56 -0600, Anthony Liguori wrote:
> Avi Kivity wrote:
> >
> >> The thing I'm trying to get at is a quantitative statement about why 
> >> moving the pit into the kernel is the right thing.  I'll try to give 
> >> the patches a try myself in the next couple of days.  I don't think 
> >> it's obvious that it's the right thing to do without some sort of 
> >> benchmark supporting it.
> >>   
> >
> > 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 tried out WinXP with the standard HAL and the in-kernel APIC patches.  
> I did not see any appreciable improvement in multimedia playback (video 
> or audio).  I still get the same amount of jitters.  I've tried with and 
> without -tdf too.
> 
> So far, the smoothest play back I've gotten is using the ACPI HAL.  Can 
> you point to a particular example where you see an improvement?  Perhaps 
> a divx or movie trailer that is better with it than without it?
> 

ACPI HAL should perform good. 
The in kernel PIT should fix time drift on standard HAL when playing
movies (pit freq -> 1000hz) and the host cpu is loaded.
If the host is not loaded you might not see the drift.
Use kernel build or tgz + taskset to load the cpu.

Without the patches in-kernel PIC should time drift and userspace PIC +
-tdf shouldn't.

As for quality, sometimes when time drifts the movies looks smoother but
that's not really the required result.

> Regards,
> 
> Anthony Liguori
> 
> 


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