netdev - Re: [PATCH 2/2] ixgbe: fix select

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Message-ID: <20090321123914.31cac36c@s6510>
Date:	Sat, 21 Mar 2009 12:39:13 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
Cc:	David Miller <davem@...emloft.net>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 2/2] ixgbe: fix select_queue management (v2)

On Sat, 21 Mar 2009 00:43:40 -0700 (Pacific Daylight Time)
"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com> wrote:

> On Sat, 21 Mar 2009, David Miller wrote:
> 
> > From: "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
> > Date: Fri, 20 Mar 2009 23:21:38 -0700 (Pacific Daylight Time)
> > 
> > > I see your point, but it is a hack in my opinion.  The device will have 8 
> > > real Tx queues, not 1.  I'd much rather go with the original proposal, 
> > > since if the code in dev_pick_tx() changed, it could silently break ixgbe.
> > 
> > It can't, if you only advertise one transmit queue the kernel
> > can never ever choose anything other than queue zero.  It's
> > impossible.
> > 
> > Stephen's right, you guys don't need your select queue override.
> > 
> > And if you recall I suspected this from the very beginning.
> > 
> > You guys never ever think out of the box, ever...  if it's
> > not straightforward, you guys won't got for it.  That makes
> > it very frustrating to get anything done.
> 
> This patch will break DCB in ixgbe.  We need all 8 queues, because the 
> user will be assigning tc filters to the sch_multiq qdisc to get traffic 
> into priority queues.  If we take Stephen's patch and tell the stack we 
> have 1 real_num_tx_queues, then we get 1 band in sch_multiq, which makes 
> it impossible to assign traffic to priorities 1 through 8:
> 

How does it make sense to say you have 8 bands, but only use one.
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