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

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Message-Id: <20070925.192811.08341847.davem@davemloft.net>
Date:	Tue, 25 Sep 2007 19:28:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hadi@...erus.ca
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	kaber@...sh.net, dada1@...mosbay.com, johnpol@....mipt.ru
Subject: Re: [RFC][NET_SCHED] explict hold dev tx lock

From: jamal <hadi@...erus.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@...erus.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 :)
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