Re: [Xen-devel] [RFC v1 14/15] Suppress posting interrupts when 'SN' is set

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 30/03/15 03:11, Wu, Feng wrote:
>
>> -----Original Message-----
>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>> Sent: Friday, March 27, 2015 9:49 PM
>> To: Wu, Feng; xen-devel@xxxxxxxxxxxxx
>> Cc: Zhang, Yang Z; Tian, Kevin; keir@xxxxxxx; JBeulich@xxxxxxxx
>> Subject: Re: [Xen-devel] [RFC v1 14/15] Suppress posting interrupts when 
>> 'SN' is
>> set
>>
>> On 27/03/15 13:45, Wu, Feng wrote:
>>>> -----Original Message-----
>>>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>>>> Sent: Friday, March 27, 2015 8:06 PM
>>>> To: Wu, Feng; xen-devel@xxxxxxxxxxxxx
>>>> Cc: Zhang, Yang Z; Tian, Kevin; keir@xxxxxxx; JBeulich@xxxxxxxx
>>>> Subject: Re: [Xen-devel] [RFC v1 14/15] Suppress posting interrupts when
>> 'SN' is
>>>> set
>>>>
>>>> On 27/03/15 03:00, Wu, Feng wrote:
>>>>>>>     static void vmx_deliver_posted_intr(struct vcpu *v, u8 vector)
>>>>>>>     {
>>>>>>> +    int r, sn;
>>>>>>> +
>>>>>>>         if ( pi_test_and_set_pir(vector, &v->arch.hvm_vmx.pi_desc) )
>>>>>>>             return;
>>>>>>>
>>>>>>> +    /*
>>>>>>> +     * Currently, we don't support urgent interrupt, all interrupts
>>>>>>> +     * are recognized as non-urgent interrupt, so we cannot send
>>>>>>> +     * posted-interrupt when 'SN' is set.
>>>>>>> +     */
>>>>>>> +
>>>>>>> +    sn = pi_test_sn(&v->arch.hvm_vmx.pi_desc);
>>>>>> Is there anywhere which sets sn at all? I cant spot anywhere.
>>>>>>
>>>>> SN is set in [13/15] while vCPU is going to runnable state.
>>>> Then please do not set SN in the first place if we don't support it.
>>> What do you mean here. Setting 'SN' can suppress non-urgent interrupt. (we
>> only support this)
>>
>> Sorry, in which case patch 13 shouldn't clear SN then.
>>
>> Either way - we should not be fixing up something in this patch which
>> was introduced in the previous patch.
> I think there are some misunderstanding here. 
>
> - In patch 13, we need to set 'SN', so as to suppress the interrupts when vCPU
> is in runnable state, since we don't need to send notification event then.
> - Here in patch 14, it is another story. From hardware p.o.v, if 'SN' is set, 
> it doesn't
> send notification event. vmx_deliver_posted_intr() is the software way to 
> delivery
> posted-interrupts, so we need to follow the HW's behavior. Hence we check 'SN'
> first, and not send notification event if it is set.

Ah I see.  Thanks for the clarification.

~Andrew

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