Subject: Re: Ethernet frame padding changes
To: Charles M. Hannum <>
From: Manuel Bouyer <>
List: tech-kern
Date: 07/06/2004 19:59:08
On Tue, Jul 06, 2004 at 11:51:27AM +0000, Charles M. Hannum wrote:
> > > to require padding always fits with a single mbuf, and in this case it is
> > > always most efficient to just pad it with 0s in core before sending it to
> > > the device.  Even using an extra DMA descriptor (as in smc83c170.c) is
> > > less efficient.
> >
> > Are we sure that the mbuf will never point to external storage for small
> > packets ? At the time I did the fixes, I didn't find anything proving that
> > this couldn't happen.
> There's no absolute guarantee of that, but that doesn't prevent making the 
> common case optimal.

I'm not sure it would be more efficient. Even for small packets, you may have
a mbuf chain (and this may be the common case, in fact).

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference