RE: [PATCH] doc: announce header split deprecation

["Ding, Xuan" <xuan.ding@intel.com>]

Hi,

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Thursday, July 14, 2022 9:25 PM
> To: Ding, Xuan <xuan.ding@intel.com>; andrew.rybchenko@oktetlabs.ru;
> ferruh.yigit@xilinx.com
> Cc: mdr@ashroe.eu; dev@dpdk.org; stephen@networkplumber.org;
> mb@smartsharesystems.com; dev@dpdk.org; Zhang, Qi Z
> <qi.z.zhang@intel.com>; asekhar@marvell.com; pbhagavatula@marvell.com;
> grive@u256.net
> Subject: Re: [PATCH] doc: announce header split deprecation
> 
> 14/07/2022 14:54, Ding, Xuan:
> > Hi,
> >
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 14/07/2022 07:50, Ding, Xuan:
> > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > 23/05/2022 16:20, xuan.ding@intel.com:
> > > > > > From: Xuan Ding <xuan.ding@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@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-w
> > enxuanx.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.

Thanks for your clarification. It's clearer now.
I was trying to figure out the whole history of header split,
seems it is not enough.

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

Agree. It is better to point out the remaining per queue
rx offload RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT for splitting packets.

Please see v2 after I add more header split background.

Regards,
Xuan

>