Re: new ipdelay= option for faster netboot

David Miller wrote:

From: Tim Bird <redacted>
Date: Mon, 17 Aug 2009 15:35:01 -0700

quoted

Tim Bird wrote:

quoted

See the definitions of CONF_PRE_OPEN and CON_POST_OPEN
in net/ipv4/ipconfig.c

They are set to ridiculously long values.  In my experience,
you can cut them down considerably with no dangerous side
effects (but I haven't asked the network guys about the
possible downsides).

It turns out that others have seen this delay.  Simon
Arlott recently posted a patch to make the delay avoidable
at boot time from the kernel command line.

See http://patchwork.kernel.org/patch/31678/

"Rediculiously long" is a relative term.

No offense intended.  I could have phrased this
better.  The delays were a few orders of
magnitude longer than apparently needed, on my
embedded test systems with ethernet.  I didn't
try eliminating them completely, as in the Arlott patch.

1.5 seconds is a long time for me.  My bootup time budget for
the kernel ranges from 0.5 to 3.0 seconds, depending on the
product.

I have card/switch combinations that take up to 10 seconds to
negotiate a proper link.

What types of delays are these timeouts supposed to
cover?  Networking delays or hardware bring-up delays?
(Or both)?  If for networking delays, is this for all
types of networks, or just some (e.g. ones that create
virtual circuits)?

I'm trying to get a sense for whether the card/switch
combinations that would take this long would be encountered
in the types of embedded devices I code for.  (TVs, camcorders,
etc.)

So what's there now is actually a quite agressive setting.

And BTW, discussions about stuff like this belong on
netdev@vger.kernel.org, which has been added to the CC:

I was going to wait to see if this solved Robert's
problem, before widening the discussion.  But I'm happy
to find out more about these delays now.

Thanks,
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================