Re: [RFC][NET_SCHED] explict hold dev tx lock

[David Miller <davem@davemloft.net>]

From: jamal <hadi@cyberus.ca>
Date: Wed, 19 Sep 2007 22:43:03 -0400

> [NET_SCHED] explict hold dev tx lock
> 
> For N cpus, with full throttle traffic on all N CPUs, funneling traffic
> to the same ethernet device, the devices queue lock is contended by all
> N CPUs constantly. The TX lock is only contended by a max of 2 CPUS.
> In the current mode of operation, after all the work of entering the
> dequeue region, we may endup aborting the path if we are unable to get
> the tx lock and go back to contend for the queue lock. As N goes up,
> this gets worse.
> 
> The changes in this patch result in a small increase in performance
> with a 4CPU (2xdual-core) with no irq binding. Both e1000 and tg3
> showed similar behavior;
> 
> Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>

I've applied this to net-2.6.24, although I want to study more deeply
the implications of this change myself at some point :)