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 10:18 AM, Zhang, Yang Z <yang.z.zhang@xxxxxxxxx> wrote:
> 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.

Sorry, I misread the original patch.

>> 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.

Got it, thanks.

 -George

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel