Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table

[Avi Kivity]

On Tue, Nov 26, 2013 at 3:47 PM, Paolo Bonzini <address@hidden> wrote:

Il 26/11/2013 14:18, Avi Kivity ha scritto:

>
>> I don't think a workqueue is even needed.  You just need to use call_rcu
>> to free "old" after releasing kvm->irq_lock.
>>
>> What do you think?
>
> Can this cause an interrupt to be delivered to the wrong (old) vcpu?

No, this would be exactly the same code that is running now:

        mutex_lock(&kvm->irq_lock);
        old = kvm->irq_routing;
        kvm_irq_routing_update(kvm, new);
        mutex_unlock(&kvm->irq_lock);

        synchronize_rcu();
        kfree(old);
        return 0;

Except that the kfree would run in the call_rcu kernel thread instead of
the vcpu thread.  But the vcpus already see the new routing table after
the rcu_assign_pointer that is in kvm_irq_routing_update.

I understood the proposal was also to eliminate the synchronize_rcu(), so while new interrupts would see the new routing table, interrupts already in flight could pick up the old one.