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

[Keir Fraser <keir@xxxxxxx>]

On 06/09/2012 11:00, "Li, Jiongxi" <jiongxi.li@xxxxxxxxx> wrote:

>>>  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 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. 
> 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.

Should cause EOI to induce VMExit only when there is more periodic timer
work to be done? That would be better than this hack.

 -- Keir



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