[dpdk-dev] [PATCH] ethdev: add flow tag

[Yongseok Koh]

> On Jul 5, 2019, at 11:05 AM, Yongseok Koh <yskoh at mellanox.com> wrote:
> 
> 
> 
>> On Jul 5, 2019, at 6:54 AM, Adrien Mazarguil <adrien.mazarguil at 6wind.com> wrote:
>> 
>> On Thu, Jul 04, 2019 at 04:23:02PM -0700, Yongseok Koh wrote:
>>> A tag is a transient data which can be used during flow match. This can be
>>> used to store match result from a previous table so that the same pattern
>>> need not be matched again on the next table. Even if outer header is
>>> decapsulated on the previous match, the match result can be kept.
>>> 
>>> Some device expose internal registers of its flow processing pipeline and
>>> those registers are quite useful for stateful connection tracking as it
>>> keeps status of flow matching. Multiple tags are supported by specifying
>>> index.
>>> 
>>> Example testpmd commands are:
>>> 
>>> flow create 0 ingress pattern ... / end
>>>   actions set_tag index 2 value 0xaa00bb mask 0xffff00ff /
>>>           set_tag index 3 value 0x123456 mask 0xffffff /
>>>           vxlan_decap / jump group 1 / end
>>> 
>>> flow create 0 ingress pattern ... / end
>>>   actions set_tag index 2 value 0xcc00 mask 0xff00 /
>>>           set_tag index 3 value 0x123456 mask 0xffffff /
>>>           vxlan_decap / jump group 1 / end
>>> 
>>> flow create 0 ingress group 1
>>>   pattern tag index is 2 value spec 0xaa00bb value mask 0xffff00ff /
>>>           eth ... / end
>>>   actions ... jump group 2 / end
>>> 
>>> flow create 0 ingress group 1
>>>   pattern tag index is 2 value spec 0xcc00 value mask 0xff00 /
>>>           tag index is 3 value spec 0x123456 value mask 0xffffff /
>>>           eth ... / end
>>>   actions ... / end
>>> 
>>> flow create 0 ingress group 2
>>>   pattern tag index is 3 value spec 0x123456 value mask 0xffffff /
>>>           eth ... / end
>>>   actions ... / end
>>> 
>>> Signed-off-by: Yongseok Koh <yskoh at mellanox.com>
>> 
>> Hi Yongseok,
>> 
>> Only high level questions for now, while it unquestionably looks useful,
>> from a user standpoint exposing the separate index seems redundant and not
>> necessarily convenient. Using the following example to illustrate:
>> 
>> actions set_tag index 3 value 0x123456 mask 0xfffff
>> 
>> pattern tag index is 3 value spec 0x123456 value mask 0xffffff
>> 
>> I might be missing something, but why isn't this enough:
>> 
>> pattern tag index is 3 # match whatever is stored at index 3
>> 
>> Assuming it can work, then why bother with providing value spec/mask on
>> set_tag? A flow rule pattern matches something, sets some arbitrary tag to
>> be matched by a subsequent flow rule and that's it. It even seems like
>> relying on the index only on both occasions is enough for identification.
>> 
>> Same question for the opposite approach; relying on the value, never
>> mentioning the index.
>> 
>> I'm under the impression that the index is a hardware-specific constraint
>> that shouldn't be exposed (especially since it's an 8-bit field). If so, a
>> PMD could keep track of used indices without having them exposed through the
>> public API.
> 
> 
> Thank you for review, Adrien.
> Hope you are doing well. It's been long since we talked each other. :-)
> 
> Your approach will work too in general but we have a request from customer that
> they want to partition this limited tag storage. Assuming that HW exposes 32bit
> tags (those are 'registers' in HW pipeline in mlx5 HW). Then, customers want to
> store multiple data even in a 32-bit storage. For example, 16bit vlan tag, 8bit
> table id and 8bit flow id. As they want to split one 32bit storage, I thought it
> is better to provide mask when setting/matching the value. Even some customer
> wants to store multiple flags bit by bit like ol_flags. They do want to alter
> only partial bits.
> 
> And for the index, it is to reference an entry of tags array as HW can provide
> larger registers than 32-bit. For example, mlx5 HW would provide 4 of 32b
> storage which users can use for their own sake.
> 	tag[0], tag[1], tag[2], tag[3]

Adrien,

Are you okay with this?

Thanks,
Yongseok