Re: [KVM PATCH v2 1/2] KVM: export lockless GSI attribute

Avi Kivity
2009-10-25T14:30:23Z

On 10/23/2009 04:38 AM, Gregory Haskins wrote:
> Certain GSI's support lockless injecton, but we have no way to detect
> which ones at the GSI level. Knowledge of this attribute will be
> useful later in the series so that we can optimize irqfd injection
> paths for cases where we know the code will not sleep. Therefore,
> we provide an API to query a specific GSI.
>
>

Instead of a lockless attribute, how about a ->set_atomic() method. For
msi this can be the same as ->set(), for non-msi it can be a function
that schedules the work (which will eventually call ->set()).

The benefit is that we make a decision only once, when preparing the
routing entry, and install that decision in the routing entry instead of
making it again and again later.

> +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq)
>

bool kvm_irq_check_lockless(...)

> +{
> + struct kvm_kernel_irq_routing_entry *e;
> + struct kvm_irq_routing_table *irq_rt;
> + struct hlist_node *n;
> + int ret = -ENOENT;
> +
> + rcu_read_lock();
> + irq_rt = rcu_dereference(kvm->irq_routing);
> + if (irq< irq_rt->nr_rt_entries)
> + hlist_for_each_entry(e, n,&irq_rt->map[irq], link)
> + ret = e->lockless ? 1 : 0;
>

ret = e->lockless;

> + rcu_read_unlock();
> +
> + return ret;
> +}
> +
>

--
error compiling committee.c: too many arguments to function