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

[Julien Grall <julien.grall@xxxxxxx>]

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@xxxxxxx>
> > ---
> >   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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