Re: [dpdk-dev] [PATCH v6 1/2] ethdev: introduce generic IP/UDP tunnel checksum and TSO

[Olivier Matz <olivier.matz@6wind.com>]

On Wed, Apr 18, 2018 at 08:02:35PM +0200, Thomas Monjalon wrote:
> 18/04/2018 18:45, Ananyev, Konstantin:
> > From: Thomas Monjalon
> > > 18/04/2018 15:58, Xueming Li:
> > > > The new flag PKT_TX_TUNNEL_IP is redundant with PKT_TX_OUTER_IP_CKSUM.
> > > > The old flag PKT_TX_OUTER_IP_CKSUM can be deprecated and removed in
> > > > later release.
> > > >
> > > > Signed-off-by: Xueming Li <xuemingl@mellanox.com>
> > > 
> > > Except a small comment below, it looks OK.
> > > 
> > > Acked-by: Thomas Monjalon <thomas@monjalon.net>
> > > 
> > > Please send a deprecation notice for PKT_TX_OUTER_IP_CKSUM.
> > 
> > I probably missed something, but why PKT_TX_OUTER_IP_CKSUM
> > is supposed to be deprecated?
> 
> Because PKT_TX_TUNNEL_* flags sepersede it. I think we need to discuss it.
> 
> We use the offload flags PKT_TX_TUNNEL_* when we request some offloads
> in the outer and the inner headers at the same time.
> When setting a tunnel flag PKT_TX_TUNNEL_*, it can be expected that
> the outer checksums will be offloaded, otherwise it is almost
> impossible to request an offload in the inner header.
> In the case of an UDP tunnel, any change in the inner packet will
> require an UDP checksum update.
> In the case of an IP tunnel, a change of the inner packet size
> (like TSO) will require an IP checksum update.
> 
> If we really require PKT_TX_OUTER_IP_CKSUM to be set in addition to
> PKT_TX_TUNNEL_* flags, then we should add more PKT_TX_OUTER_*_CKSUM,
> like PKT_TX_OUTER_UDP_CKSUM which is missing.

I agree, I think PKT_TX_TUNNEL_* implies PKT_TX_OUTER_IP_CKSUM.
And I don't see use-case where we only need PKT_TX_OUTER_IP_CKSUM,
because in that case we can use PKT_TX_IP_CKSUM.

But this can be discussed in a second step, for now I think it's safer
to keep it as is.

Olivier