[dpdk-dev] [PATCH v8 2/2] doc: annouce deprecation of jumbo frame flag condition

[Ananyev, Konstantin]

> On 11/2/2020 1:18 PM, Andrew Rybchenko wrote:
> > On 11/2/20 11:52 AM, SteveX Yang wrote:
> >> Annouce to replace 'RTE_ETHER_MAX_LEN' with 'RTE_ETHER_MTU' as type
> >> condition of jumbo frame. Involved scopes:
> >> - rte_ethdev;
> >> - app, e.g.: test-pmd, test-eventdev;
> >> - examples, e.g.: ipsec-secgw, l3fwd, vhost;
> >> - net PMDs which support VLAN tag(s) within overhead, e.g.: i40e, ixgbe;
> >>
> >> Signed-off-by: SteveX Yang <stevex.yang at intel.com>
> >> ---
> >>   doc/guides/rel_notes/deprecation.rst | 12 ++++++++++++
> >>   1 file changed, 12 insertions(+)
> >>
> >> diff --git a/doc/guides/rel_notes/deprecation.rst
> >> b/doc/guides/rel_notes/deprecation.rst
> >> index 2e082499b..fae139f01 100644
> >> --- a/doc/guides/rel_notes/deprecation.rst
> >> +++ b/doc/guides/rel_notes/deprecation.rst
> >> @@ -138,6 +138,18 @@ Deprecation Notices
> >>     will be limited to maximum 256 queues.
> >>     Also compile time flag ``RTE_ETHDEV_QUEUE_STAT_CNTRS`` will be removed.
> >> +* ethdev: Offload flag ``DEV_RX_OFFLOAD_JUMBO_FRAME`` will be set according to
> >> +  ``RTE_ETHER_MTU`` in next release. Currently, the jumbo frame uses the
> >> +  ``RTE_ETHER_MAX_LEN`` as boundary condition. When the MTU (1500) set, the
> >> +  frame type of rx packet will be different if used different overhead, it will
> >> +  cause the consistency issue. Hence, using fixed value ``RTE_ETHER_MTU`` can
> >> +  avoid this issue.
> >> +  Following scopes will be changed:
> >> +  - ``rte_ethdev``
> >> +  - ``app``, e.g.: ``test-pmd``, ``test-eventdev``;
> >> +  - ``examples``, e.g.: ``ipsec-secgw``, ``l3fwd``, ``vhost``;
> >> +  - net PMDs which support VLAN tag(s) within overhead, e.g.: ``i40e``;
> >> +
> >>   * cryptodev: support for using IV with all sizes is added, J0 still can
> >>     be used but only when IV length in following structs
> >> ``rte_crypto_auth_xform``,
> >>     ``rte_crypto_aead_xform`` is set to zero. When IV length is greater or equal
> >>
> >
> > If so, what's the point to have the offload? May be just deprecate and
> > later remove it?
> >

Same thought actually, can we remove DEV_RX_OFFLOAD_JUMBO_FRAME flag completely?
PMD can decide based on provided MTU size does segmentation, etc. is needed.

> 
> Above just changes the condition of what is called jumbo frame, nothing more.
> 
> ethdev assumes max frame size (without jumbo frame support) can be
> 'RTE_ETHER_MAX_LEN' (1518)
> 
> But a PMD can support double VLAN, and it can have RTE_ETHER_MAX_LEN + 8 bytes
> frame size and still may not support jumbo frame.
> 
> In that case ethdev overwrites the frame size as RTE_ETHER_MAX_LEN, and this
> will reduce the supported MTU to 1492 (instead of expected 1500).
> Above deprecation notice is to fix this.