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

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Message-Id: <1181262703.3688.10.camel@w-sridhar2.beaverton.ibm.com>
Date:	Thu, 07 Jun 2007 17:31:43 -0700
From:	Sridhar Samudrala <sri@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	hadi@...erus.ca, auke-jan.h.kok@...el.com, jeff@...zik.org,
	kaber@...sh.net, peter.p.waskiewicz.jr@...el.com,
	netdev@...r.kernel.org, jesse.brandeburg@...el.com
Subject: Re: [PATCH] NET: Multiqueue network device support.

On Thu, 2007-06-07 at 16:00 -0700, David Miller wrote:
> From: jamal <hadi@...erus.ca>
> Date: Thu, 07 Jun 2007 18:54:08 -0400
> 
> > On Thu, 2007-07-06 at 15:44 -0700, David Miller wrote:
> > > From: jamal <hadi@...erus.ca>
> > > Date: Thu, 07 Jun 2007 17:57:25 -0400
> > > 
> > > > I empathize but take a closer look; seems mostly useless.
> > > 
> > > I thought E1000 still uses LLTX, and if so then multiple cpus can most
> > > definitely get into the ->hard_start_xmit() in parallel.
> > 
> > AFAICS, only one CPU can dequeue from the qdisc i.e s/he who holds
> > __LINK_STATE_QDISC_RUNNING is the only one who can call qdisc_restart
> > and only s/he can enter ->hard_start_xmit().
> > 
> > Am i missing something?
> 
> That's right we fixed that the other week.

If the QDISC_RUNNING flag guarantees that only one CPU can call
dev->hard_start_xmit(), then why do we need to hold netif_tx_lock
for non-LLTX drivers?

Thanks
Sridhar

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