From: Ben Greear <redacted>
Date: Thu, 26 Aug 2010 21:14:39 -0700

I'll look into the NET_XMIT_CN, but if that propagates backpressure up
through mac-vlan, then something must know how to re-start the tx
logic.

It doesn't need to, as it drops and frees up the packet.

One thing that really bothers me about the current qdisc stuff is that
it just frees the packet when it cannot accept it.

Without the drop, things like RED simply would not work.

This *should* allow us to better throttle UDP sockets without
dropping as many packets on the sending side, and would probably
help TCP as well.

UDP is well throttled by the socket send buffer.

The only problematic case is pktgen and it's an abberation and
an obscure case.  It's in fact trying to bypass all of the
queueing and accounting the stack normally makes use of.