Re: [Xen-devel] [PATCH] xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next online VCPU

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

>  
>  static int set_affinity_irq(struct irq_data *data, const struct cpumask 
> *dest,
>                           bool force)
> diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
> index 10f1ef5..1192f24 100644
> --- a/drivers/xen/evtchn.c
> +++ b/drivers/xen/evtchn.c
> @@ -58,6 +58,8 @@
>  #include <xen/xen-ops.h>
>  #include <asm/xen/hypervisor.h>
>  
> +static DEFINE_PER_CPU(int, bind_last_selected_cpu);

This should be moved into evtchn_bind_interdom_next_vcpu() since that's
the only place referencing it.

Why is it a percpu variable BTW? Wouldn't making it global result in
better interrupt distribution?

> +
>  struct per_user_data {
>       struct mutex bind_mutex; /* serialize bind/unbind operations */
>       struct rb_root evtchns;
> @@ -421,6 +423,36 @@ static void evtchn_unbind_from_user(struct per_user_data 
> *u,
>       del_evtchn(u, evtchn);
>  }
>  
> +static void evtchn_bind_interdom_next_vcpu(int evtchn)
> +{
> +     unsigned int selected_cpu, irq;
> +     struct irq_desc *desc = NULL;
> +     unsigned long flags;
> +
> +     irq = irq_from_evtchn(evtchn);
> +     desc = irq_to_desc(irq);
> +
> +     if (!desc)
> +             return;
> +
> +     raw_spin_lock_irqsave(&desc->lock, flags);
> +     selected_cpu = this_cpu_read(bind_last_selected_cpu);
> +     selected_cpu = cpumask_next_and(selected_cpu,
> +                     desc->irq_common_data.affinity, cpu_online_mask);
> +
> +     if (unlikely(selected_cpu >= nr_cpu_ids))
> +             selected_cpu = cpumask_first_and(desc->irq_common_data.affinity,
> +                             cpu_online_mask);
> +
> +     raw_spin_unlock_irqrestore(&desc->lock, flags);

I think if you follow Juergen's suggestion of wrapping everything into
irq_enable/disable you can drop the lock altogether (assuming you keep
bind_last_selected_cpu percpu).

-boris


> +     this_cpu_write(bind_last_selected_cpu, selected_cpu);
> +
> +     local_irq_disable();
> +     /* unmask expects irqs to be disabled */
> +     xen_rebind_evtchn_to_cpu(evtchn, selected_cpu);
> +     local_irq_enable();
> +}
> +
>


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