Re: [Xen-devel] [PATCH v4] x86/apicv: fix RTC periodic timer and apicv issue

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

On January 03, 2017 4:23 PM, Jan Beulich wrote:
>>>> On 03.01.17 at 09:15, <xuquan8@xxxxxxxxxx> wrote:
>
>>
>>>-----Original Message-----
>>>From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>>>Sent: Tuesday, January 03, 2017 3:35 PM
>>>To: Xuquan (Quan Xu)
>>>Cc: Andrew Cooper; George Dunlap; yang.zhang.wz@xxxxxxxxx; Chao
>Gao;
>>>Jun Nakajima; Kevin Tian; Lan Tianyu; xen-devel@xxxxxxxxxxxxx
>>>Subject: RE: [PATCH v4] x86/apicv: fix RTC periodic timer and apicv
>>>issue
>>>
>>>>>> On 23.12.16 at 13:24, <xuquan8@xxxxxxxxxx> wrote:
>>>> On December 22, 2016 4:12 PM, Jan Beulich wrote:
>>>>>>>> On 21.12.16 at 06:44, <xuquan8@xxxxxxxxxx> wrote:
>>>>>> --- a/xen/arch/x86/hvm/vmx/intr.c
>>>>>> +++ b/xen/arch/x86/hvm/vmx/intr.c
>>>>>> @@ -315,9 +315,13 @@ void vmx_intr_assist(void)
>>>>>>          * Set eoi_exit_bitmap for periodic timer interrup to
>>>>>> cause
>>>>>EOI-induced VM
>>>>>>          * exit, then pending periodic time interrups have the
>>>>>> chance
>>>>>to be injected
>>>>>>          * for compensation
>>>>>> +        * Set eoi_exit_bitmap for intack.vector when it's higher
>>>>>> + than
>>>>>pending
>>>>>> +        * periodic time interrupts. This way we can guarantee
>>>>>> + there's
>>>>>always a chance
>>>>>> +        * to post periodic time interrupts when periodic time
>>>>>interrupts becomes the
>>>>>> +        * highest one
>>>>>>          */
>>>>>>          if (pt_vector != -1)
>>>>>> -            vmx_set_eoi_exit_bitmap(v, pt_vector);
>>>>>> +            vmx_set_eoi_exit_bitmap(v, intack.vector);
>>>>>
>>>>>The comment does not clarify why max(pt_vector, intack.vector) is
>>>>>not needed. And I'd expect you to add ASSERT(intack.vector >=
>>>>>pt_vector) then, to prove this (and one might argue that this
>>>>>addition could be sufficient documentation, albeit perhaps a brief
>>>>>comment next to the assertion would help readers of this non-trivial
>piece of code).
>>>>>
>>>> Kevin or Jan..
>>>> ASSERT(...) is ok to me.. Could you help me give a brief comment?
>>>
>>>I don't see why you couldn't simply use what Kevin said in reply to my
>>>earlier question regarding the lack of max() here.
>>>
>>
>> What about """ Set EOI exit bitmap for any vector which may block
>> injection of pt_vector - give a chance to recognize pt_vector in
>> future intack and then do pt interrupts post"""?
>
>To me that doesn't explain the absence of max(pt_vector, intack.vector)
>here.
>

intack.vector is the highest priority vector..

Jan, thanks for your patience.. then, I'd say:
"""
intack.vector is the highest priority vector. So we set eoi_exit_bitmap
for intack.vector - give a chance to post periodic time interrupts when
periodic time interrupts become the highest one.
"""

If this is still not the comment you want, could you help me enhance it?

Quan 



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