Re: [PATCH] doc: announce header split deprecation

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

On 7/14/2022 4:58 PM, Ferruh Yigit wrote:
> 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.
> 
> As far as I understand 'BUFFER_SPLIT' has a target to split package 
> based on size, to various size mempools, and it can split the payload as 
> well without caring the protocol headers.
> Most probably practical usage is to split inner protocol, but protocol 
> not needed to be known by NIC, it can still split based on size.
> 

Ahh, deprecation notice is to deprecate 'HEADER_SPLIT', not other way 
around as I got it wrongly.

I think both may have use case, specially for NICs that parse the 
protocols, header split can be easier to use.
But since there is no user for a long time, perhaps that is not a real 
life need, and we can always add it back when needed, hence:

Acked-by: Ferruh Yigit <ferruh.yigit@xilinx.com>


> 
> Also as far as I can see mlx5 implemented the feature [1], contradicting 
> the claim in the commit log, again Slava can comment better. (Although I 
> don't see any PMD claim "Buffer Split on Rx" feature supported.)
> 
> 
> [1]
> Commit 9f209b59c8b0 ("net/mlx5: support Rx buffer split description")
> 
>>>
>>> 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.
>>
> 
> I can't see a v2 in patchwork, is a v2 sent? If so, may be something 
> went wrong.
>