Re: add back pending timer irqs for kernel APIC timer

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Dong, Eddie wrote:
> Avi Kivity wrote:
>   
>> Dong, Eddie wrote:
>>     
>>>     Add back pending irqs for apic timer to get precise guest    
>>> APIC timer interrupt. 
>>>
>>>       
>> Can you explain the problem and the solution in more detail?
>>     
>
> Today guest sleep 10 seconds only get about 5-6 seconds in host time.
> A design philosiphy in various VMM is that guest wall clock should catch
> up host wall clock. 
>
> The reason (partly) is that A VM may be descheduled, while the host time
> is still going.  For periodic timer like APIC timer, guest expect to see
> certain amount of interrupt that stands for the time passed (host time).
> In previous
> APIC timer virtualization policy, we inject an IRQ to APIC when a period
> of  host time is passed, but the guest may not take it if it is
> descheduled.
> In that way the previous irq in APIC will be overwritten by next
> injection from fire of 
> host hrtimer.  In that way guest get less amount of APIC timer IRQ.
>
> This patch keep track of the pending irqs and inject them back to guest
> eventually
> even the guest may be descheduled. This is also what we did in Xen.
> BTW, This policy will also be applied to future kernel PIT, I just do it
> step by step.
>
>   

I see.  We have something like that in userspace (called the 
time-drift-fix, or tdf).  Will look at the patch now.


-- 
error compiling committee.c: too many arguments to function


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