Re: How do I use multiqueue tx

[David Miller <davem@davemloft.net>]

From: Andrew Gallatin <gallatin@myri.com>
Date: Tue, 03 Jun 2008 11:34:18 -0400

> I've done a patch to myri10ge which enables the use of multiple
> transmit queues in our Linux driver using CONFIG_NETDEVICES_MULTIQUEUE
> netdev subqueues.  Our current hardware uses multiple queues purely
> for increasing host parallelism, not priority/QOS.  I'm looking for a
> way, beyond pktgen, to actually use any transmit queue other than 0 to
> increase parallelism.

Even though there are seperate per-TX-queue start/stop states
available to manage, all of the transmit path still uses a
single global lock to manage the packet queue in the generic
device structure.

So you will get zero extra parallelism by using the other queues.

I plan to work on this and have presented my ideas about how to
solve this problem in two presentations I gave in Japan several
months ago, and last week in Berlin.

http://vger.kernel.org/~davem/davem_tokyo08.pdf
http://vger.kernel.org/~davem/davem_berlin08.pdf

Don't even bother trying to get better TX parallelism at the
current time, it'll be so much easier to accomplish after
I do this development which I anticipate should be in a testable
state in about one month.