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

[Chao Gao <chao.gao@xxxxxxxxx>]

On Thu, Feb 23, 2017 at 11:55:15AM +0000, Xuquan (Quan Xu) wrote:
>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 am afraid it is not right. when the 'current' wants to deliver posted
interrupt to 'current', the vcpu is running and cpu == smp_processor_id().  

>
>I think we could simplify __vmx_deliver_posted_interrupt():
>
>   1. set VCPU_KICK_SOFTIRQ bit of v->processor.

Do we need set VCPU_KICK_SOFTIRQ bit when vcpu is not running? IMO, if vcpu is
not running, just unblock (or, vcpu_kick since when vcpu is not running,
vcpu_kick is the same with vcpu_unblock )is enough.

>   2. IF vcpu is running:
>         - send_IPI

Do we need send self-IPI when the target vcpu is 'current'? IMO, set
VCPU_KICK_SOFTIQR is enough.  

>     ELSE
>         - vcpu_kick
>
>
>Thank you for your patience..
>Quan
>
>

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