[Codel] hardware multiqueue in fq_codel?

[Eric Dumazet]

On Mon, 2013-07-15 at 15:40 +0200, Jesper Dangaard Brouer wrote:

> Then they should also be smart enough to change their default fq_codel
> qdisc, to be a prio band based qdisc... shouldn't they ;-)
> 


Some companies do this classification at the edge of their network, so
that they do not have to worry for each machine of their fleet.

Forcing them to learn how to 'fix' things once a new linux version is
installed would be quite lame. I wont be the guy responsible for this.

Listen, there is no point trying to tell me how fq_codel is better than
pfifo_fast. Is an apple better than an orange ?

Instead, we only have to create a clear path.

1) Allow the default qdisc to be specified/chosen in Kconfig, a bit
  like tcp congestion module (cubic is the default)

2) Allow the default qdisc to be selected by a /proc/sys entry, like TCP
congestion module.

3) Define the PRIO + codel/band0 + fq_codel/band1 + codel/band2 as a new
standalone qdisc

4) Eventually switch the default Kconfig from pfifo_fast to this beast.

By the way, tcp_cong.c has a race in its list handling, list_move() is
not RCU compatable.