Messages in this thread | | | Subject | Re: [PATCH] xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next online VCPU | From | Anoob Soman <> | Date | Mon, 5 Jun 2017 11:14:42 +0100 |
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On 02/06/17 17:24, Boris Ostrovsky wrote: >> >> 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.
Sure, I will do it.
> > Why is it a percpu variable BTW? Wouldn't making it global result in > better interrupt distribution?
The reason for percpu instead of global, was to avoid locking. We can have a global variable (last_cpu) without locking, but value of last_cpu wont be consistent, without locks. Moreover, since irq_affinity is also used in the calculation of cpu to bind, having a percpu or global wouldn't really matter, as the result (selected_cpu) is more likely to be random (because different irqs can have different affinity). What do you guys suggest.
> >> + >> 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 >
I think we would still require spin_lock(). spin_lock is for irq_desc.
>> + 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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