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

["Xuquan (Quan Xu)" <xuquan8@xxxxxxxxxx>]

On February 23, 2017 7:01 PM, Jan Beulich wrote:
>>>> On 23.02.17 at 11:53, <xuquan8@xxxxxxxxxx> wrote:
>> On February 23, 2017 5:59 PM, Jan Beulich wrote:
>>>>>> On 23.02.17 at 10:28, <xuquan8@xxxxxxxxxx> wrote:
>>>> On February 18, 2017 12:33 AM, Jan Beulich wrote:
>>>>>>>> On 17.02.17 at 09:49, <chao.gao@xxxxxxxxx> wrote:
>>>>>>>diff --git a/xen/arch/x86/hvm/vmx/vmx.c
>>>b/xen/arch/x86/hvm/vmx/vmx.c
>>>>>>>index 61925cf..3887c32 100644
>>>>>>>--- a/xen/arch/x86/hvm/vmx/vmx.c
>>>>>>>+++ b/xen/arch/x86/hvm/vmx/vmx.c
>>>>>>>@@ -1846,8 +1846,7 @@ static void
>>>>>__vmx_deliver_posted_interrupt(struct vcpu *v)
>>>>>>>     {
>>>>>>>         unsigned int cpu = v->processor;
>>>>>>>
>>>>>>>-        if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ,
>>>>>&softirq_pending(cpu))
>>>>>>>-             && (cpu != smp_processor_id()) )
>>>>>>>+        if ( !softirq_pending(cpu) && (cpu != smp_processor_id())
>>>>>>>+ )
>>>>
>>>> Jan,
>>>>     could you help me present the definition of ' smp_processor_id()'
>and '
>>>> current' in __vmx_deliver_posted_interrupt() ? thanks..
>>>
>>>I'm afraid I don't understand the request.
>>
>> 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?
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


Thank you for your patience..
Quan



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