Re: [net-next PATCH 14/14] net: sched: pfifo_fast use skb_array

On Thu, Dec 7, 2017 at 9:58 AM, John Fastabend [off-list ref] wrote:

This converts the pfifo_fast qdisc to use the skb_array data structure
and set the lockless qdisc bit. pfifo_fast is the first qdisc to support
the lockless bit that can be a child of a qdisc requiring locking. So
we add logic to clear the lock bit on initialization in these cases when
the qdisc graft operation occurs.

This also removes the logic used to pick the next band to dequeue from
and instead just checks a per priority array for packets from top priority
to lowest. This might need to be a bit more clever but seems to work
for now.

A very dumb question:

Why do we call it lockless? With skb_array you just shift the per qdisc
spinlock down to each pfifo band, skb_array still uses a spinlock underneath.

What am I missing here?