netdev - Re: tc H/W offload issue with vxlan tunnels [was: nfp: flower vxlan tunnel offload]

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Date:   Wed, 27 Sep 2017 14:31:36 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Or Gerlitz <gerlitz.or@...il.com>, Jiri Benc <jbenc@...hat.com>,
        Simon Horman <simon.horman@...ronome.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com, John Hurley <john.hurley@...ronome.com>,
        Paul Blakey <paulb@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>
Subject: Re: tc H/W offload issue with vxlan tunnels [was: nfp: flower vxlan
 tunnel offload]

On Wed, 2017-09-27 at 13:11 +0200, Jiri Pirko wrote:
> Wed, Sep 27, 2017 at 11:46:58AM CEST, pabeni@...hat.com wrote:
> > On Wed, 2017-09-27 at 11:17 +0200, Jiri Pirko wrote:
> > > Wed, Sep 27, 2017 at 10:29:35AM CEST, pabeni@...hat.com wrote:
> > > > So it looks like the H/W offload hook will still be called with the
> > > > same arguments in both case, and 'bad' rule will still be pushed to the
> > > > H/W as the driver itself has no way to distinct between the two
> > > > scenarios.
> > > 
> > > Why "bad"?
> > 
> > Such rule is coped differently by the SW and the HW data path.
> > 
> > a rule like:
> > 
> > tc filter add dev eth0 protocol ip parent ffff: flower \
> >   enc_key_id 102 enc_dst_port 4789 src_ip 3.4.5.6 skip_hw \
> >   action action mirred redirect eth0_vf_1
> > 
> > will match 0 packets, while:
> > 
> > tc filter add dev eth0 protocol ip parent ffff: flower \
> >   enc_key_id 102 enc_dst_port 4789 src_ip 3.4.5.6 skip_sw \
> >   action action mirred redirect eth0_vf_1
> > 
> > [just flipped 'skip_sw' and 'skip_hw' ]
> > will match the vxlan-tunneled packets. I understand that one of the
> > design goal for the h/w offload path is being consistent with the sw
> > one, but that does not hold in the above scenario.
> 
> Sure, the consistency is important. Howcome "skip_hw" won't match and
> "skip_sw" will match? What's different?

For the SW datapath, we need a metadata based/lwt tunnel to collect the
tunnel information. eth0 is not a such device and does not provide the
metadata. Any match on tunnel based field will fail - correctly.

When the HW datapath is used, the underlaying NIC is programmed exactly
as done when we replace eth0 with vxlan0. The programmed flow matches
vxlan encapsulated traffic.

Cheers,

Paolo