[PATCH] doc: announce header split deprecation

[Thomas Monjalon]

14/07/2022 14:54, Ding, Xuan:
> Hi,
> 
> From: Thomas Monjalon <thomas at monjalon.net>
> > 14/07/2022 07:50, Ding, Xuan:
> > > From: Thomas Monjalon <thomas at monjalon.net>
> > > > 23/05/2022 16:20, xuan.ding at intel.com:
> > > > > From: Xuan Ding <xuan.ding at intel.com>
> > > > >
> > > > > RTE_ETH_RX_OFFLOAD_HEADER_SPLIT offload was introduced some
> > time
> > > > ago
> > > > > to substitute bit-field header_split in struct rte_eth_rxmode. It
> > > > > allows to enable header split offload with the header size
> > > > > controlled using split_hdr_size in the same structure.
> > > > >
> > > > > Right now, no single PMD actually supports
> > > > > RTE_ETH_RX_OFFLOAD_HEADER_SPLIT with above definition. Many
> > > > > examples and test apps initialize the field to 0 explicitly. The
> > > > > most of drivers simply ignore split_hdr_size since the offload is
> > > > > not advertised, but
> > > > some double-check that its value is 0.
> > > > >
> > > > > So the RTE_ETH_RX_OFFLOAD_HEADER_SPLIT and split_header_size
> > field
> > > > > will be removed in DPDK 22.11.
> > > > >
> > > > > Signed-off-by: Xuan Ding <xuan.ding at intel.com>
> > > > > ---
> > > > >  doc/guides/rel_notes/deprecation.rst | 4 ++++
> > > > >  1 file changed, 4 insertions(+)
> > > > >
> > > > > diff --git a/doc/guides/rel_notes/deprecation.rst
> > > > > b/doc/guides/rel_notes/deprecation.rst
> > > > > index 4e5b23c53d..b8114f29ed 100644
> > > > > --- a/doc/guides/rel_notes/deprecation.rst
> > > > > +++ b/doc/guides/rel_notes/deprecation.rst
> > > > > @@ -125,3 +125,7 @@ Deprecation Notices
> > > > >    applications should be updated to use the ``dmadev`` library instead,
> > > > >    with the underlying HW-functionality being provided by the ``ioat`` or
> > > > >    ``idxd`` dma drivers
> > > > > +
> > > > > +* ethdev: After bit-field header split was removed, the
> > > > > +``RTE_ETH_RX_OFFLOAD_HEADER_SPLIT``
> > > > > +offload and the ``split_hdr_size`` field in structure
> > > > > +``rte_eth_rxmode`` to enable header split offload are not
> > > > > +supported in any
> > > > PMDs. They will be removed in DPDK 22.11.
> > > >
> > > > It would have been good to talk about rte_eth_rxseg_split which is
> > > > similar and configured per-queue.
> > >
> > > Thanks for your suggestion.
> > >
> > > But I'm a little confused, are you referring that I need to involve protocol
> > based buffer split?
> > > About the deprecation of header split, I haven't realized its connection to
> > rte_eth_rxseg_split.
> > 
> > What???
> > In old versions of your patch "ethdev: introduce protocol type based header
> > split"
> > you wrote:
> > "
> > A new proto field is introduced in the
> > rte_eth_rxseg_split structure reserved field to specify header protocol type.
> > With Rx offload flag RTE_ETH_RX_OFFLOAD_HEADER_SPLIT enabled and
> > protocol type configured, PMD will split the ingress packets into two separate
> > regions.
> > "
> 
> It has a long history... 
> It was corrected in v4 that RTE_ETH_RX_OFFLOAD_HEADER_SPLIT is used to enable header
> split offload with the header size controlled using "split_hdr_size".
> But no single PMD actually supports RTE_ETH_RX_OFFLOAD_HEADER_SPLIT for this purpose.
> So we finally decide to deprecate this flag.
> 
> http://patchwork.dpdk.org/project/dpdk/patch/20220402104109.472078-2-wenxuanx.wu@intel.com/
> 
> In following series, I use RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT instead. It is for multi-segments packet
> split. And it still needs a "proto_hdr" field in rte_eth_rxmode to configure split location.

I know this history because I was the one asking you to deprecate this.
But it seems you didn't get the big picture.

> > > Currently there are 2 acks, add more PMD maintainers to help review
> > > this deprecation notice for header split, thanks a lot!
> > 
> > I cannot say my feeling strong enough.
> 
> So IMO the deprecation for header split is not relevant with buffer split. But we can still clean the code.
> Hope it make things clearer.

They are almost the same features.
So when deprecating one, it is important to mention what remains.
If needed RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT can still be used
and it is configured per-queue,
while RTE_ETH_RX_OFFLOAD_HEADER_SPLIT was configurable per-port.

Andrew, Ferruh, do you agree to improve this deprecation notice
by adding above information?