Re: [Xen-devel] [PATCH 2/4] VMX: Turn on posted interrupt bit in vmcs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.13 at 10:30, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
> Jan Beulich wrote on 2013-04-09:
>>>>> On 09.04.13 at 08:01, Yang Zhang <yang.z.zhang@xxxxxxxxx> wrote:
>>> --- a/xen/include/asm-x86/mach-default/irq_vectors.h
>>> +++ b/xen/include/asm-x86/mach-default/irq_vectors.h
>>> @@ -9,12 +9,13 @@
>>>  #define CALL_FUNCTION_VECTOR       0xfb
>>>  #define LOCAL_TIMER_VECTOR 0xfa
>>>  #define PMU_APIC_VECTOR    0xf9
>>> +#define POSTED_INTERRUPT_VECTOR    0xf8
>> 
>> Is it really necessary to use a static, high priority vector here?
> There is an corner case. During vmenty, cpu will not respond external 
> interrupt. And it is possible that posted interrupt and another interrupt are 
> pending in IRR. We hope posted interrupt have high priority and it can be 
> consumed immediately after vmentry finished. Or else, there may two separate 
> interrupt arrived in hypervisor.

If there is a window, using a static, high priority vector only shrinks
its size. If what you describe is an actual problem (and not just a
latency issue), then it needs to be fixed properly rather just lowering
its likelihood to occur. And if it isn't, I think you ought to demonstrate
that using a static vector indeed provides meaningful benefit over
a dynamically allocated one.

Jan


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