From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [RFC PATCH] kvm: Extend irqfd to support level interrupts
Date: Mon, 18 Jun 2012 08:27:51 -0600
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Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	"mtosatti@redhat.com" <mtosatti@redhat.com>,
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To: Avi Kivity <avi@redhat.com>
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On Mon, 2012-06-18 at 13:14 +0300, Avi Kivity wrote:
> On 06/18/2012 01:11 PM, Michael S. Tsirkin wrote:
> 
> >> (vhost,
> >> msi-less ivshmem clone)?
> > 
> > I guess vhost can poll eventfd and reinject an interrupt.
> > Of course to bypass qemu completely we also need to support reads over
> > ioeventfd somehow.
> > 
> 
> eventfd is not suitable for level triggered interrupts as far as I can
> tell.  It's about passing edges, and level interrupts aren't.  We need
> something like a pipe for communicating state (or just use KVM_IRQ_LINE).

Isn't level just two edges with a state in between?  Sure we may be
unnecessarily de-asserting for brief periods, but for an external
assigned device, we don't know whether it's unnecessary.  Thanks,

Alex