Re: [PATCH] doc: announce header split deprecation

[Ferruh Yigit <ferruh.yigit@xilinx.com>]

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.

> 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>
>>
>