Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors

On 10/15/2014 01:40 PM, Rusty Russell wrote:

Jason Wang [off-list ref] writes:

quoted

Below should be useful for some experiments Jason is doing.
I thought I'd send it out for early review/feedback.

event idx feature allows us to defer interrupts until
a specific # of descriptors were used.
Sometimes it might be useful to get an interrupt after
a specific descriptor, regardless.
This adds a descriptor flag for this, and an API
to create an urgent output descriptor.
This is still an RFC:
we'll need a feature bit for drivers to detect this,
but we've run out of feature bits for virtio 0.X.
For experimentation purposes, drivers can assume
this is set, or add a driver-specific feature bit.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <redacted>

The new VRING_DESC_F_URGENT bit is theoretically nicer, but for
networking (which tends to take packets in order) couldn't we just set
the event counter to give us a tx interrupt at the packet we want?

Cheers,
Rusty.

Yes, we could. Recent RFC of enabling tx interrupt use this.