Re: [PATCH RFC 00/11] ixgbe/mbuf: add TSO support

[Stephen Hemminger <stephen-OTpzqLSitTUnbdJkjeBofR2eb7JE58TQ@public.gmane.org>]

On Fri, 09 May 2014 23:49:45 +0200
Olivier MATZ <olivier.matz-pdR9zngts4EAvxtiuMwx3w@public.gmane.org> wrote:

> Hi Stephen,
> 
> On 05/09/2014 07:04 PM, Stephen Hemminger wrote:
> > I would also like to propose changing the checksum offload flags.
> > Many devices can indicate good checksum in some cases but can't test
> > for many other types of packets. By changing the flags to be:
> >  PKT_RX_L4_CKSUM_GOOD and PKT_RX_IP_CKSUM_GOOD
> > 
> > It is then possible to support devices where some cases (IPv4 + TCP)
> > are supported but others are not.
> 
> I agree. That's also what I'm talking about in the commit log of
> the patch 08/11.
> 
> If there is not much rework for all the patches, I think it's feasible
> to include this kind of modification in the v2 of this series.
> 
> Regards,
> Olivier
> 

There are three checksum states:
	1. Known good
	2. Known bad
	3. Can't tell

Current choice of flags makes handling #3 impossible. If you change it to CKSUM_GOOD
then 1 => GOOD, 2 => not GOOD, 3 => not GOOD. And for case #3 the software can
validate it.  For most cases IP checksum offload is meaning less anyway because
the IP header fits in a single cache line, and the cost to checksum is minimal.