netdev - RE: 2.6.27 problem with shaping using netem/ifb (regression?) [TSO]

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Date:	Wed, 01 Oct 2008 21:55:42 -0400
From:	Patrick McManus <mcmanus@...ksong.com>
To:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Cc:	netdev@...r.kernel.org
Subject: RE: 2.6.27 problem with shaping using netem/ifb (regression?) [TSO]

On Wed, 2008-10-01 at 18:42 -0700, Brandeburg, Jesse wrote:
> > Any thoughts on where to look? I hope attaching the script is helpful
> -
> > it is pretty self evident when running it if things are working ok.
> > This
> > is all on amd64 if that is relevant.
> 
> Have you tried disabling TSO and/or GSO on the loopback device?

for some reason with loopback that didn't come to mind. It's a good
suggestion, and indeed is the crux of the problem. Thanks!

Disabling TSO (ethtool -K lo tso off) fixes the problem. GSO has no
impact.

probly not relevant, but worth noting - the scripts also set the MTU of
lo to 1500 down from the default 16436


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