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

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Date:	Thu, 7 Jun 2007 09:59:14 -0700
From:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
To:	"Stephen Hemminger" <shemminger@...ux-foundation.org>,
	"David Miller" <davem@...emloft.net>
Cc:	<hadi@...erus.ca>, <kaber@...sh.net>, <netdev@...r.kernel.org>,
	<jeff@...zik.org>, "Kok, Auke-jan H" <auke-jan.h.kok@...el.com>
Subject: RE: [PATCH] NET: Multiqueue network device support.

> > 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.
> 
> There could be bad packet reordering with this (like some SMP 
> routers used to do).

My original multiqueue patches I submitted actually had a per-queue Tx
lock, but it was removed since the asymmetry in the stack for locking
was something people didn't like.  Locking a queue for ->enqueue(),
unlocking, then locking for ->dequeue(), unlocking, was something people
didn't like very much.  Also knowing what queue to lock on ->enqueue()
was where the original ->map_queue() idea came from, since we wanted to
lock before calling ->enqueue().

-PJ
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