Re: [Xen-devel] [PATCH] x86/apicv: enhance posted-interrupt processing

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.02.17 at 12:55, <xuquan8@xxxxxxxxxx> wrote:
> On February 23, 2017 7:01 PM, Jan Beulich wrote:
>>>>> On 23.02.17 at 11:53, <xuquan8@xxxxxxxxxx> wrote:
>>> IOW,
>>>  which vcpu does the 'current' refer to?
>>>  which cpu does the ' smp_processor_id()' refer to?
>>
>>current: currently running vCPU
> 
> in a SMP machine, are there more than one currently running vCPU?

Of course. "current" obviously is the one running on the CPU we're
on.

> I think so, the condition "if ( running && (in_irq() || (v != current)) )", 
> in 
> __vmx_deliver_posted_interrupt() looks strange -- when vCPU is running, why 
> to 
> check ' v != current '..
> 
> 
>>smp_processor_id(): processor ID of the CPU we're running on
>>
> I think if vcpu is running, ' cpu != smp_processor_id() ' should be true.
> 
> 
> I think we could simplify __vmx_deliver_posted_interrupt():
> 
>    1. set VCPU_KICK_SOFTIRQ bit of v->processor.
>    2. IF vcpu is running:
>          - send_IPI
>      ELSE
>          - vcpu_kick

If this can be done in a race free manner (after all, the running
state of a vCPU running on another pCPU may change at any
time) ...

Jan


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