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

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Date:	Fri, 20 Mar 2009 10:14:38 -0700 (Pacific Daylight Time)
From:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
To:	Stephen Hemminger <shemminger@...tta.com>
cc:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	David Miller <davem@...emloft.net>,
	"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

On Fri, 20 Mar 2009, Stephen Hemminger wrote:

> On Fri, 20 Mar 2009 00:23:39 -0700 (Pacific Daylight Time)
> "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com> wrote:
> 
> > On Thu, 19 Mar 2009, Stephen Hemminger wrote:
> > 
> > > Convert ixgbe to use net_device_ops properly.
> > > Rather than changing the select_queue function pointer
> > > just check the flag.
> > > 
> > > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > Thanks Stephen.  I was looking at reassigning a DCB netdev_ops struct when 
> > DCB is enabled, and then having a default netdev_ops struct when it's not 
> > enabled.  I agree the check is cleaner the way you have it below, but it's 
> > another conditional check in the Tx hotpath, which we have too many of in 
> > the first place.
> 
> Changing number of tx queues is actually the fastest, since then
> indirection is not needed
> 
> > On a related side note, why is the netdev_ops member of net_device 
> > declared const?
> 
> The purpose of having an ops structure is two fold. First, the ops
> can be in read-only section (if driver wants) to avoid cache issues.
> More importantly only one instance is necessary when there are multiple
> boards, or 1000's of vlans.

Ah, gotcha.  Clears up my questions.

Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
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