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Re: [Qemu-devel] [PATCH v2 2/3] virtio-mmio: introduce set_guest_notifie
Re: [Qemu-devel] [PATCH v2 2/3] virtio-mmio: introduce set_guest_notifiers
Fri, 08 May 2015 09:45:00 +0300
> Hm, weren't there some patches for irqfd on arm?
Yes, there were. However, they had a design problem by breaking backwards
with unmodified virtio. Their idea was to set up one more shared memory area
virtio and vhost-net and use it to pass ISR value, which helps to distinguish,
took place (queue update or config change). So, this idea was rejected.
I thought about it, and technically, i think, this can be done in better way.
as far as i understood, all we need is mechanism for distinguishing between
events. On PCI we do this by using multiple IRQs via MSI-X, and one IRQ signals
one type of event. MSI-X code also has "two IRQs" mode as a failsafe, where one
signals config change and another IRQ signals queues update (and all queues are
turn). I think a similar thing could be done for virtio-mmio. It could allocate
instead of one and describe both of them in the device tree. Guest side, upon
could make use of those two IRQs and acknowledge to the host side that "yes, i
version and use new mode".
But, sorry, i will unlikely implement this, because we already have PCI with
hope this is going to be published soon), so my project can use PCI emulation.
implementing irqfds for virtio-mmio is a bit out of my scope.
Samsung Electronics Research center Russia