Re: [PATCH] Deferrable Timer

[Dave Winchell <dwinchell@virtualiron.com>]

Yu, Ke wrote:

>Keir Fraser wrote:
>  
>
>>On 17/7/08 13:54, "Yu, Ke" <ke.yu@intel.com> wrote:
>>
>>    
>>
>>>This patch adds new ac timer API set_timer_deferrable for the
>>>deferrable timer.
>>>      
>>>
>>Whether this is worthwhile depends on what likely users there are.
>>platform-timer overflow is not very compelling since if you're using
>>anything other than PIT (which ought to be likely on a modern system
>>supporting deep sleep) the overflow period should be multiple seconds.
>>
>> -- Keir
>>    
>>
>
>True. Another user is the Px state sampling timer, which is 20ms. Other
>potential timers (e.g. sched timer, hvm pt timers) are also under
>evaluation, the principle is to make sure there is no performance
>downgrade.
>  
>
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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