RE: [PATCH] doc: announce header split deprecation

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

Hi,

> -----Original Message-----
> From: Slava Ovsiienko <viacheslavo@nvidia.com>
> Sent: Friday, July 15, 2022 12:56 AM
> To: Ferruh Yigit <ferruh.yigit@xilinx.com>; Ding, Xuan
> <xuan.ding@intel.com>; NBU-Contact-Thomas Monjalon (EXTERNAL)
> <thomas@monjalon.net>; andrew.rybchenko@oktetlabs.ru
> Cc: mdr@ashroe.eu; dev@dpdk.org; stephen@networkplumber.org;
> mb@smartsharesystems.com; 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
> 
> > -----Original Message-----
> > From: Ferruh Yigit <ferruh.yigit@xilinx.com>
> > Sent: Thursday, July 14, 2022 18:58
> > To: Ding, Xuan <xuan.ding@intel.com>; NBU-Contact-Thomas Monjalon
> > (EXTERNAL) <thomas@monjalon.net>; andrew.rybchenko@oktetlabs.ru;
> Slava
> > Ovsiienko <viacheslavo@nvidia.com>
> > Cc: mdr@ashroe.eu; dev@dpdk.org; stephen@networkplumber.org;
> > mb@smartsharesystems.com; 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
> >
> > On 7/14/2022 3:07 PM, Ding, Xuan wrote:
> > > 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.
> > >
> >
> > Isn't the intention of 'RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT' &
> > 'RTE_ETH_RX_OFFLOAD_HEADER_SPLIT' are different?
> > Cc'ed Slava for more comment.
> 
> Hi, thank you for Cc'ing
> 
> Yes, you are right, we have two splitting offloads, and these ones have the
> different intentions. As there are no PMDs actually handling
> RTE_ETH_RX_OFFLOAD_HEADER_SPLIT, there should be no objections for
> this deprecation.

Thanks for helping review.

For 'BUFFER_SPLIT', I think it is clear. As Ferruh explains, it is used for splitting packets into multi-segments and multi-mempools based on rte_eth_rxseg_split.
Right now only mlx5 supports this offload.

For 'HEADER_SPLIT', IMO it is used for splitting packets into two segments based on the split_hdr_size in rte_eth_rxmode.
And header split does not support split into multi-mempools(the same mempool).

So at this level, we can say that header split and buffer split are the same intention (split packets).
The functions supported by header split have been covered by buffer split. And no PMD actually supports 'HEADER_SPLIT'.

Please corrects me if my understanding is wrong.

Thanks,
Xuan


> 
> Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
>