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

["Yu, Ke" <ke.yu@xxxxxxxxx>]

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. so is the
"guest-does-not-handle-missed-ticks" case, since xen can handle that by
inject missed tick respectively. 

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
>>> 
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> 
> 
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