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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

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?

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)?

 -George

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