RE: [PATCH] doc: announce header split deprecation

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

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@xilinx.com>
> Sent: Friday, July 15, 2022 7:34 PM
> To: Ding, Xuan <xuan.ding@intel.com>; Slava Ovsiienko
> <viacheslavo@nvidia.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
> 
> On 7/15/2022 9:28 AM, Ding, Xuan wrote:
> > 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).
> >
> 
> I looks like we don't have much details on the intention of the
> 'HEADER_SPLIT', it is not well documented.

Yes, since no PMD supports this offload, we should remove it
to make code cleaner.

Thanks,
Xuan

> 
> > 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>
> >>
> >