Re: [Xen-devel] [PATCH] Remove a set operation for VCPU_KICK_SOFTIRQ when post interrupt to vm.

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

George Dunlap wrote on 2015-09-23:
> On Wed, Sep 23, 2015 at 8:42 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 23.09.15 at 05:50, <yang.z.zhang@xxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>> @@ -1678,8 +1678,9 @@ 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 ( !test_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu)) +   
>>>          && pi_test_on(&v->arch.hvm_vmx.pi_desc) +             && (cpu
>>> != smp_processor_id()))
>>>              send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
>>>      }
>>>  }
>> 
>> So this still removes the setting of the softirq - how can that be
>> correct (namely in the cpu == smp_processor_id() case)? Did you
>> perhaps mean
>> 
>>         if ( pi_test_on(&v->arch.hvm_vmx.pi_desc)
>>              && !test_and_set_bit(VCPU_KICK_SOFTIRQ,
>>              &softirq_pending(cpu)) && (cpu != smp_processor_id()))
> 
> So the problem before was setting the SOFTIRQ for another cpu but then
> never sending an interrupt?

No, the problem is the setting SOFTIRQ doesnât be cleared in time and cause the 
subsequent interrupt injection be delayed.

> 
> Is there a reason why this code isn't using cpu_raise_softirq() here,
> rather than manually doing the same thing (and doing it incorrectly, 
> apparently)?

The vector is different which uses posted_intr_vector here not 
EVENT_CHECK_VECTOR.

> 
>  -George


Best regards,
Yang


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