Re: [Xen-devel] [ PATCH 2/2] xen: enable Virtual-interrupt delivery

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2012-09-06:
>>>> On 06.09.12 at 12:00, "Li, Jiongxi" <jiongxi.li@xxxxxxxxx> wrote:
>>> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx]
>>> On 31/08/2012 10:30, "Li, Jiongxi" <jiongxi.li@xxxxxxxxx> wrote:
>>>> --- a/xen/arch/x86/hvm/irq.c  Fri Aug 31 09:30:38 2012 +0800
>>>> +++ b/xen/arch/x86/hvm/irq.c         Fri Aug 31 09:49:39 2012 +0800
>>>> @@ -452,7 +452,11 @@ struct hvm_intack hvm_vcpu_ack_pending_i
>>>> 
>>>>  int hvm_local_events_need_delivery(struct vcpu *v) {
>>>> -    struct hvm_intack intack = hvm_vcpu_has_pending_irq(v);
>>>> +    struct hvm_intack intack;
>>>> +
>>>> +    pt_update_irq(v);
>>> 
>>> Why would this change be needed for vAPIC?
>> When vcpu is scheduled out, there will be periodic timer interrupt pending
> 
> Probably rather "may"?

yes, there may have pending timer interrupt.

>> for injection. Every VMExit is a chance to inject the pending periodic timer
>> interrupt on vmx_intr_assist. In no virtual interrupt delivery case, although
>> injected timer interrupt is edge trigger, EOI always induces VMExit, pending
>> periodic timer can be kept injected till there is no pending left. But in
>> virtual interrupt delivery case, only level trigger interrupt can induce
>> VMExit, there is much less chance for injecting pending timer interrupt
>> through VMExit.
> 
> And it's not possible to set the respective VIRR[] bit, and let the
> hardware take care of injecting at the right time?

Right, we can use this way to inject the interrupt. 
But it still need a watchdog to aware when the bit in VIRR is cleared by guest, 
and the cost is same with forcing VM exit when writing EOI for timer interrupt.

>> Adding pt_update_irq here is another code path to inject pending periodic
>> timer, but it can't guarantee every pending timer interrupt can be injected.
>> Another way is to make every EOI of pending timer interrupt induce VMExit,
>> but it may obey the spirit of virtual interrupt delivery - reducing VMExit.
>> We have been evaluating that.
> 
> With which result?

We are doing it now. Will let you know the result when get it.

> Jan
> 
> 
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Best regards,
Yang



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