Re: [PATCH] Deferrable Timer

[Dave Winchell <dwinchell@virtualiron.com>]

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
>>>>
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>>>>
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>>    
>>
>
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