From: Hannes Frederic Sowa <redacted>
Date: Mon, 01 Sep 2014 22:05:42 +0200

But as soon as we try to make Qdiscs absolutely lockless, we don't have
any guard that we don't concurrently dequeue skbs from it and suddenly
one Qdisc dequeue processing entity couldn't notify the driver that the
end of the batching was reached. I think this could become a problem
depending on how much of the locking is removed?

I am certain that batching will require taking the device transmit
lock over the ->ndo_start_xmit() invocations, and therefore the
deferral decisions must atomically be made inside of that context.