[kvm-devel] [RFC] Remove tx_timer from virtio_net

[Anthony L. <ali...@us...>]

Avi and I were talking this afternoon and he suggested that we should 
remove the tx_timer from the virtio_net front-end and replace it with a 
tx_timer in the backend.

Since the backend can suppress notifications, this is appealing since it 
gives much more flexibility to the backend in determining how to do tx 
batching.  I've done a quick implementation and performance is pretty good.

We may need an ABI change, however.  When the backend disables 
notifications, there is absolutely no way for the frontend to notify 
anymore.  In the case where the queue fills up, it cannot flush since 
the backend has disabled notifications.  To work around this, I had to 
least notifications enabled and check for the case where the queue fills 
up manually.

I think a possible solution to this would be to differentiate between a 
soft and hard notify.  We would introduce a VRING_USED_F_NOTIFY_ON_FULL 
and a VRING_AVAIL_F_NOTIFY_ON_FULL.

The NO_NOTIFY variants would indicate that the other end never sends a 
notify, whereas NOTIFY_ON_FULL would indicate that the other end never 
sends a notify unless the queue fills up.

Regards,

Anthony Liguori