Re: [PATCH v3] ethdev: deprecate header fields and metadata flow actions

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

On 11/25/2021 2:13 PM, Slava Ovsiienko wrote:
>> -----Original Message-----
>> From: Thomas Monjalon <thomas@monjalon.net>
>> Sent: Thursday, November 25, 2021 15:07
>> To: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>; Ajit Khaparde
>> <ajit.khaparde@broadcom.com>; Somnath Kotur
>> <somnath.kotur@broadcom.com>; Rahul Lakkireddy
>> <rahul.lakkireddy@chelsio.com>; Slava Ovsiienko <viacheslavo@nvidia.com>;
>> Ferruh Yigit <ferruh.yigit@intel.com>
>> Cc: dev@dpdk.org; Ori Kam <orika@nvidia.com>
>> Subject: Re: [PATCH v3] ethdev: deprecate header fields and metadata flow
>> actions
>>
>> 25/11/2021 12:53, Ferruh Yigit:
>>> On 11/24/2021 3:37 PM, Viacheslav Ovsiienko wrote:
>>>> The generic RTE_FLOW_ACTION_TYPE_MODIFY_FIELD action was
>> introduced
>>>> by [1]. This action provides an unified way to perform various
>>>> arithmetic and transfer operations over packet network header fields
>>>> and packet metadata.
>>>>
>>>> [1] commit 641dbe4fb053 ("net/mlx5: support modify field flow
>>>> action")
>>>>
>>>> On other side there are a bunch of multiple legacy actions, that can
>>>> be superseded by the generic modify field action:
>>>>
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_MPLS_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_DEC_MPLS_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_NW_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_DEC_NW_TTL      sfc
>>>> RTE_FLOW_ACTION_TYPE_OF_COPY_TTL_OUT
>>>> RTE_FLOW_ACTION_TYPE_OF_COPY_TTL_IN
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_SRC       bnxt, cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_DST       bnxt, cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_SRC       cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_DST       cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_TP_SRC         cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_TP_DST         cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_DEC_TTL            mlx5, sfc
>>>> RTE_FLOW_ACTION_TYPE_SET_TTL            mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_MAC_SRC        cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_MAC_DST        cxgbe, mlx5
>>>> RTE_FLOW_ACTION_TYPE_INC_TCP_SEQ        mlx5
>>>> RTE_FLOW_ACTION_TYPE_DEC_TCP_SEQ        mlx5
>>>> RTE_FLOW_ACTION_TYPE_INC_TCP_ACK        mlx5
>>>> RTE_FLOW_ACTION_TYPE_DEC_TCP_ACK        mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_DSCP      mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_DSCP      mlx5
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_VLAN_VID    bnxt, cnxk, cxgbe, enic,
>>>>                                           mlx5, octeontx2, sfc
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_VLAN_PCP    bnxt, cnxk, cxgbe, enic,
>>>>                                           mlx5, octeontx2, sfc
>>>> RTE_FLOW_ACTION_TYPE_SET_TAG            mlx5
>>>> RTE_FLOW_ACTION_TYPE_SET_META           mlx5
>>>>
>>>> This note deprecates the following RTE Flow actions:
>>>> 1. As not supported by any of PMDs:
>>>>
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_MPLS_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_DEC_MPLS_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_SET_NW_TTL
>>>> RTE_FLOW_ACTION_TYPE_OF_COPY_TTL_OUT
>>>> RTE_FLOW_ACTION_TYPE_OF_COPY_TTL_IN
>>>>
>>>> 2. As supposed to be replaced by generig field modify action:
>>>> RTE_FLOW_ACTION_TYPE_OF_DEC_NW_TTL
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_SRC
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_DST
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_SRC
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_DST
>>>> RTE_FLOW_ACTION_TYPE_SET_TP_SRC
>>>> RTE_FLOW_ACTION_TYPE_SET_TP_DST
>>>> RTE_FLOW_ACTION_TYPE_DEC_TTL
>>>> RTE_FLOW_ACTION_TYPE_SET_TTL
>>>> RTE_FLOW_ACTION_TYPE_SET_MAC_SRC
>>>> RTE_FLOW_ACTION_TYPE_SET_MAC_DST
>>>> RTE_FLOW_ACTION_TYPE_INC_TCP_SEQ
>>>> RTE_FLOW_ACTION_TYPE_DEC_TCP_SEQ
>>>> RTE_FLOW_ACTION_TYPE_INC_TCP_ACK
>>>> RTE_FLOW_ACTION_TYPE_DEC_TCP_ACK
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV4_DSCP
>>>> RTE_FLOW_ACTION_TYPE_SET_IPV6_DSCP
>>>> RTE_FLOW_ACTION_TYPE_SET_TAG
>>>> RTE_FLOW_ACTION_TYPE_SET_META
>>>>
>>>> The VLAN set actions are interrelated to VLAN header
>>>> insertion/removal and supported by multiple PMDs and supposed to be
>>>> just deprecated but not be removed in 22.11.
>>>>
>>>
>>> Why not remove them for v22.11? Do you think PMDs can't change the
>>> existing implementation until 22.11?
>>>
>>>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
>>>>
>>>> --
>>>> v2  - deprecation.rst is updated
>>>> v3  - doc comments addressed
>>>>       - commit message comments addressed
>>>>       - SET_VLAN_VID and SET_VLAN_PCP actions deprecated, but will not
>>>>         be removed in 22.11
>>>
>>> Deprecated symbols are to prevent new code using them, but for this
>>> case there is no alternative, since PMDs still don't support
>>> 'RTE_FLOW_ACTION_TYPE_MODIFY_FIELD' yet.
>>
>> This patch is not preventing new code using old actions, there are just
>> comments to point to the new direction.
>>
>>> This patch is forcing users to use deprecated actions (except from mlx).
>>
>> I don't get it.
>> It is encouraging to use the new generic action, which is supported only by
>> mlx5 for now.
>>
>>
>>> What about a slight change:
>>> 1- In this release, update header/document as
>> 'RTE_FLOW_ACTION_TYPE_MODIFY_FIELD'
>>>      is preferred way if supported. Instead of deprecating old ones.
>>
>> Deprecation is just a comment, clearly showing that it may be removed in
>> future.
>> In my opinion, it makes the message simple and clear.
>>
>>
>>> 2- Have an agreement with PMD maintainers to switch to new action before
>> v22.11,
>>>      and don't accept old action implementation in PMDs anymore.
>>>      Based on agreement update 'deprecation.rst' in this release to note that
>>>      old actions will be removed on v22.11.
>>>      (It would be good to have a check to prevent old actions merged
>>> during that time.)
>>
>> Not sure I get it.
>> You want to remove VLAN actions? I think it is premature.
>>
>>> 3- In v22.11, remove old actions, the PMDs that don't support
>> MODIFY_FIELD
>>>      action will lose the feature.
>>
>> The VLAN actions are probably already used a lot in the field.
>> I would consider removing them only if it becomes a burden to maintain.
> 
> +1
> Dropping VLAN might trigger an avalanche of changes in applications - it is supported by multiple PMDs and should be widely engaged.
> Other legacy actions are supported by very limited set of drivers and usage area should be smaller, I would say risk is moderate.
> 

Got it, 'SET_VLAN*' is treat differently because its impact can be more.

Can we do the same for other implemented actions, support them longer and
give more time for deprecation.
How big will be the maintenance cost in the PMD?