Re: [RFC 2/8] xen/arm: gic: Do not configure affinity for guest IRQ during routing

[Julien Grall <julien.grall@arm.com>]

Hi Stefano,

On 22/06/16 11:54, Stefano Stabellini wrote:
> On Tue, 7 Jun 2016, Julien Grall wrote:
>> The affinity of a guest IRQ is set every time the guest enable it (see
>> vgic_enable_irqs).
>>
>> It is not necessary to set the affinity when the IRQ is routed to the
>> guest because Xen will never receive the IRQ until it hass been enabled
>> by the guest.
>>
>> Signed-off-by: Julien grall <julien.grall@arm.com>
>> ---
>>   xen/arch/arm/gic.c | 10 ++++------
>>   1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
>> index 8a1087b..f25381f 100644
>> --- a/xen/arch/arm/gic.c
>> +++ b/xen/arch/arm/gic.c
>> @@ -97,17 +97,13 @@ void gic_restore_state(struct vcpu *v)
>>   }
>>
>>   /*
>> - * needs to be called with a valid cpu_mask, ie each cpu in the mask has
>> - * already called gic_cpu_init
>>    * - desc.lock must be held
>>    * - arch.type must be valid (i.e != IRQ_TYPE_INVALID)
>>    */
>>   static void gic_set_irq_properties(struct irq_desc *desc,
>> -                                   const cpumask_t *cpu_mask,
>>                                      unsigned int priority)
>>   {
>>       gic_hw_ops->set_irq_properties(desc, priority);
>> -    desc->handler->set_affinity(desc, cpu_mask);
>>   }
>>
>>   /* Program the GIC to route an interrupt to the host (i.e. Xen)
>> @@ -123,7 +119,9 @@ void gic_route_irq_to_xen(struct irq_desc *desc, const cpumask_t *cpu_mask,
>>
>>       desc->handler = gic_hw_ops->gic_host_irq_type;
>>
>> -    gic_set_irq_properties(desc, cpu_mask, priority);
>> +    desc->handler->set_affinity(desc, cpu_mask);
>
> You could call irq_set_affinity here, it might make for nicer code.
>
> Actually thinking more about this, I think it would be better to add the
> irq_set_affinity call to xen/arch/arm/irq.c:setup_irq, right after the
> call to gic_route_irq_to_xen.  That way both gic_route_irq_to_xen and
> gic_route_irq_to_guest would behave the same way: just setup the routing
> and not the affinity.
>
> What do you think?

I am fine to call irq_set_affinity from setup_irq. It makes more sense 
than calling the former from gic_route_irq_to_xen.

I will make the change in the next version.

Cheers,

-- 
Julien Grall

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