svn commit: r299182 - head/sys/dev/e1000

[Kenneth D. Merry]

On Fri, May 06, 2016 at 15:41:38 +0000, Sean Bruno wrote:
> Author: sbruno
> Date: Fri May  6 15:41:38 2016
> New Revision: 299182
> URL: https://svnweb.freebsd.org/changeset/base/299182
> 
> Log:
>   If ALTQ is defined in the kern conf, switch to Legacy Mode.
>   
>   PR:		208409
>   Submitted by:	freebsd at mcwest.org
>   MFC after:	2 weeks
> 
> Modified:
>   head/sys/dev/e1000/if_igb.h

Just for the mail archives (and hopefully for someone who is interested in
fixing it), IGB_LEGACY_TX is broken.  (It leads to panics.)

See:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=213257
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=212413

And some comments about it in this particular bug as well:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=208409

This bit me last night on 10-stable.  I have ALTQ in my kernel
configuration, but I'm only using it on em(4) interfaces, not igb(4)
interfaces.  (I bought an em(4) NIC in mid-2015 because of this particular
problem.)

Some folks have been able to get around the problem by rate-limiting
traffic on the igb(4) interfaces, but that is fairly kludgy.

IMO, we shouldn't enable IGB_LEGACY_TX automatically when ALTQ is enabled
when it can lead to crashes.

There are several possible ways to fix things:

1. Actually fix IGB_LEGACY_TX so that it doesn't cause crashes.
2. If ALTQ is actually in use with igb(4), switch igb(4) into single queue
   mode.  (Not sure how feasible that is.)
3. Come up with a way for ALTQ to generically and easily work on top of
   multiqueue interfaces.

I'm sure other folks more well versed in the network stack will have
additional ideas.

Ken
-- 
Kenneth Merry
ken at FreeBSD.ORG