Re: [PATCH 0/2] KVM: PPC: Support ioeventfd

[Avi Kivity <avi@redhat.com>]

On 10/16/2012 12:59 PM, Alexander Graf wrote:
> 
> On 16.10.2012, at 12:56, Avi Kivity wrote:
> 
>> On 10/15/2012 02:02 PM, Alexander Graf wrote:
>>> In order to support vhost, we need to be able to support ioeventfd.
>>> 
>>> This patch set adds support for ioeventfd to PPC and makes it possible to
>>> do so without implementing irqfd along the way, as it requires an in-kernel
>>> irqchip which we don't have yet.
>> 
>> It's not strictly required.  You have an interrupt line leading to the
>> core, no?  You could have your irqfd trigger that.
> 
> The irqfd code in KVM directly triggers the in-kernel irqchip. That's what this patch set is cleaning up: enable you to build ioeventfd support without in-kernel irqchip irqfd support.
> 
> Vhost can work without in-kernel irqchip too, by listening to an eventfd (iiuc) in user space. That path works just fine with these patches applied.

That's all true but it wasn't my point.  I was asking whether you can
enable irqfd without in-kernel irqchip.  If your irq input is edge
triggered then it's trivial.  If it's level triggered then you can use
the new resampling irqfd.


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