Re: [virtio-comment] [PATCH v3] Introduction of Virtio Network device notifications coalescing feature.

[Alvaro Karsz <alvaro.karsz@solid-run.com>]

After some more thought, I'm not sure that the notifications
coalescing feature can work if VIRTIO_F_EVENT_IDX is negotiated.

Quoting Virtio Spec:
> Note: For example, if used_event is 0, then a device using VIRTIO_F_EVENT_IDX would send a used buffer notification to the driver after the first buffer is used (and again after the 65536th buffer, etc).

So, if the driver sets the event index to #X and doesn't change the
value after receiving the notification, it is meaningless to use the
interrupt coalescing parameters. since it will anyway receive a
notification every 65536 packets (uint16_t overflow).

I'm thinking of adding a constraint that the driver MUST NOT accept
this feature if VIRTIO_F_EVENT_IDX is offered by the device.
What do you think?