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

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Date:	Sun, 25 Oct 2009 16:30:12 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	alacrityvm-devel@...ts.sourceforge.net
Subject: Re: [KVM PATCH v2 1/2] KVM: export lockless GSI attribute

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

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