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

Gregory Haskins
2009-10-26T13:25:14Z

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Avi Kivity wrote:
> 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.

Yeah, I like this idea. I think we can also get rid of the custom
workqueue if we do this as well, TBD.

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

We lose the ability to detect failure (such as ENOENT) if we do this,
but its moot if we move to the ->set_atomic() model, since this
attribute is no longer necessary and this patch can be dropped.

Kind Regards,
-Greg

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