Re: [Xen-devel] [PATCH] Deferrable Timer

[Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>]

Yu, Ke wrote:

> Yu, Ke wrote:
>  
>
> > Dave,
> >
> > Glad to see there is deferrable timer application. Please go ahead
> > with that. And I will keep you updated if there is finding in my side.
> >
> > BTW, Could you please elaborate more on the
> > "guest-handles-missed-tick" case? Since there is no need to inject
> > missed tick to guest, which timer would be used as deferrable timer?
> >    
> Oh, I catch your points now, please ignore my previous question. You
> actually means that: since guest can handle the missed tick correcty, it
> is acceptable that the hpet/vpt timer is defered, so the hpet/vpt timer
> itself can be deferrable timer.
Yes.

> so is the
> "guest-does-not-handle-missed-ticks" case, since xen can handle that by
> inject missed tick respectively. 
>  
For the guest-does-not-handle-missed-ticks case we inject the correct number
of interrupts, i.e. N*period, N an integer, but we can delay a bit before
doing so. So I think we can use deferrable timers for both policies.

> If my understanding is correct, I would say your point is truly good, I
> expect this will reduce the timer count much especially when there is
> multiple HVMs. 
>
> Best Regards
> Ke
>
>  
>
> > Best Regards
> > Ke
> >
> > Dave Winchell wrote:
> >    
> >
> > > Ke,
> > >
> > > One would think that hpet or vpt support for the
> > > guest-handles-missed-ticks policy would be a good application for a
> > > deferrable timer. If a deferrable timer were used, then the
> > > comparator (cmp) would have to be warped to a non-integer multiple
> > > of the period. This is because Linux reads the comparator register
> > > to estimate the delay since the interrupt was posted.
> > > I don't think warping like this will be a problem. At some point, I
> > > can test this. 
> > >
> > > I think we could use the deferrable timer for the
> > > guest-does-not-handle-missed-ticks
> > > policy as well.
> > >
> > > Any investigation that you want to do in the platform timer area
> > > would be fine. Or I can do it, but that will probably be after I do
> > > the vpt.c/hpet.c integration work.
> > >
> > > thanks,
> > > Dave
> > >
> > >      
> > >
> > > > Best Regards
> > > > Ke
> > > >
> > > > _______________________________________________
> > > > Xen-devel mailing list
> > > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.xensource.com/xen-devel
> > > >        
> > _______________________________________________
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> > http://lists.xensource.com/xen-devel
> >    
>  

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