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

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

On Tue, 2008-03-04 at 09:52 -0600, Anthony Liguori wrote:
> Yang, Sheng wrote:
> > Hi
> >
> > Here is the last in-kernel PIT patch for KVM. The mainly change from last 
> > version is the supporting to save/restore. I also tested live migration.
> >
> > The other modifies including some date structure changed to be better for 
> > supporting the save/restore. I moved the PIT timer to outside of channel 
> > structure, which explicitly means only one channel (channel 0) would trigger 
> > it.
> >
> > After fix TSC problem on SMP PAE RHEL5/5.1 guest, now the patch works well 
> > without any modify of kernel parameter.
> >   
> 
> How are you measuring the improvements from an in-kernel PIT?  From your 
> mails, you're claiming it increases the timer accuracy.  How are you 
> measuring it and how much does it improve it?
> 

It's also a functionality addition: userspace pit & pic combination
needed to use -tdf option (time drift fix). The tdf took care of pending
pit irqs and tried to make the guest ack the right number of irqs the
pit was configured.

Once we switched to the default in-kernel pic, the userspace pit
couldn't get the acks from the pit.
One can see the effect when running multiple guests (windows, standard
HAL) playing video, the time slows down.

This patch set has a pending counter and takes care for it too.

> Do you expect an overall performance improvement from this or is it 
> simply about improving timer accuracy?
> 

It will probably help older kernels with slow HZ run faster HZ guests.
Without CONFIG_DYNTICK the guests behaved jumpy because of that.

> 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/
> _______________________________________________
> kvm-devel mailing list
> kvm-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/kvm-devel


-------------------------------------------------------------------------
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/