netdev - Re: Network drivers that don't suspend on interface down

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Message-ID: <20061220164054.GA27938@dspnet.fr.eu.org>
Date:	Wed, 20 Dec 2006 17:40:54 +0100
From:	Olivier Galibert <galibert@...ox.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Network drivers that don't suspend on interface down

On Wed, Dec 20, 2006 at 04:34:17PM +0100, Arjan van de Ven wrote:
> 5 seconds is unfair and unrealistic though. The *hardware* negotiation
> before link is seen can easily take upto 45 seconds already.
> That's a network topology/hardware issue (spanning tree fun) that
> software or even the hardware in your PC can do nothing about.

It's about ergonomics, not technical capabilities or fairness.

> this means that the "power up time" needs to be at least 45 seconds, if
> it's then down 5 seconds inbetween... that's not real power savings.

Then that means you can't have usable autodetection and power savings
at the same time.  That's a pefectly acceptable answer, you just have
to give the choice between the two to the user.  From the kernel
p.o.v, it just means that you probably need 3 modes:
1- active and exchanging packets

2- inactive but waiting for plugging and able to tell something is
   going on fast (like 0.5s fast)

3- powered off

and they probably already exist (UP+addr/procmisc. set, UP and DOWN).
And if the second mode can't be lower power than the first, that's
just life.  An hypothetical mode 4 identical to 2 without the "fast"
part is just not worth bothering with.

  OG.
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