netdev - Re: [PATCH] NET: Multiqueue network device support.

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Date:	Wed, 06 Jun 2007 16:56:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hadi@...erus.ca
Cc:	peter.p.waskiewicz.jr@...el.com, kaber@...sh.net,
	netdev@...r.kernel.org, jeff@...zik.org, auke-jan.h.kok@...el.com
Subject: Re: [PATCH] NET: Multiqueue network device support.

From: jamal <hadi@...erus.ca>
Date: Wed, 06 Jun 2007 19:35:46 -0400

> There is no potential for parallelizing on transmit that i can think of.
> Dave, please explain it slowly so i can understand it.
> 
> There is huge potential for parallelizing on receive. But i am certainly
> missing the value in the transmit.

I gave an example in another response, you have N processes
queueing up data for TCP or UDP or whatever in parallel on
different cpus, all going out the same 10gbit device.

All of them enter into ->hard_start_xmit(), and thus all of them try
to take the same netdev->tx_lock

If they have multiple TX queues, independantly programmable, that
single lock is stupid.

We could use per-queue TX locks for such hardware, but we can't
support that currently.
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