Re: [dpdk-dev] [PATCH v3] ethdev: add IPv4 and L4 checksum RSS offload types

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 7/7/21 4:00 PM, Zhang, Qi Z wrote:
> 
> 
>> -----Original Message-----
>> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> Sent: Wednesday, July 7, 2021 5:49 PM
>> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Zhang, AlvinX
>> <alvinx.zhang@intel.com>; ajit.khaparde@broadcom.com
>> Cc: dev@dpdk.org
>> Subject: Re: [PATCH v3] ethdev: add IPv4 and L4 checksum RSS offload types
>>
>> On 7/7/21 6:23 AM, Zhang, Qi Z wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>>>> Sent: Tuesday, July 6, 2021 4:05 PM
>>>> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Zhang, AlvinX
>>>> <alvinx.zhang@intel.com>; ajit.khaparde@broadcom.com
>>>> Cc: dev@dpdk.org
>>>> Subject: Re: [PATCH v3] ethdev: add IPv4 and L4 checksum RSS offload
>>>> types
>>>>
>>>> On 7/6/21 10:18 AM, Zhang, Qi Z wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Zhang, AlvinX <alvinx.zhang@intel.com>
>>>>>> Sent: Tuesday, July 6, 2021 3:06 PM
>>>>>> To: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>; Zhang, Qi Z
>>>>>> <qi.z.zhang@intel.com>; ajit.khaparde@broadcom.com
>>>>>> Cc: dev@dpdk.org
>>>>>> Subject: RE: [PATCH v3] ethdev: add IPv4 and L4 checksum RSS
>>>>>> offload types
>>>>>>
>>>>>>>> @@ -537,6 +537,8 @@ struct rte_eth_rss_conf {
>>>>>>>>  #define ETH_RSS_PPPOE		   (1ULL << 31)
>>>>>>>>  #define ETH_RSS_ECPRI		   (1ULL << 32)
>>>>>>>>  #define ETH_RSS_MPLS		   (1ULL << 33)
>>>>>>>> +#define ETH_RSS_IPV4_CHKSUM	   (1ULL << 34)
>>>>>>>> +#define ETH_RSS_L4_CHKSUM	   (1ULL << 35)
>>>>>>>
>>>>>>> What does efine which L4 protocols are supported? How user will know?
>>>>>>
>>>>>> I think if we want to support L4 checksum RSS by using below
>>>>>> command port config all rss (all|default|eth|vlan|...)
>>>>>>
>>>>>> We must define TCP/UDP/SCTP checksum RSS separately:
>>>>>> #define ETH_RSS_TCP_CHKSUM	(1ULL << 35)
>>>>>> #define ETH_RSS_UDP_CHKSUM	(1ULL << 36)
>>>>>> #deifne ETH_RSS_SCTP_CHKSUM	(1ULL << 37)
>>>>>>
>>>>>> Here 3 bits are occupied, this is not good for there are not many
>>>>>> bits
>>>> available.
>>>>>>
>>>>>> If we only want to using it in flows, we only need to define
>>>>>> ETH_RSS_L4_CHKSUM, because the flow pattern pointed out the L4
>>>>>> protocol type.
>>>>>> flow create 0 ingress pattern eth / ipv4 / tcp / end actions rss
>>>>>> types l4-chksum end queues end / end
>>>>>
>>>>> +1, the pattern already give the hint to avoid the ambiguity and I
>>>>> +think we
>>>> already have ETH_RSS_LEVEL to figure out inner or outer.
>>>>
>>>> The problem that it may be used in generic RSS flags which has no the
>> context.
>>>> Also even in the case of flow API context could have no L4 protocol at all.
>>>
>>> For generic case, it can simply assume it cover all L4 checksum cases and I'm
>> not sure if any user intend to use it as generic RSS, pmd can simply reject it if
>> it's not necessary to support.
>>
>> Try to look at it from an application point of view which does not know any
>> specifics of the driver.
>>
>>  * Get dev_info and see ETH_RSS_L4_CHKSUM, good!, would like to
>>    use it.
> 
> 
> The PMD should not expose it if it don't want to (or not able to) support all l4 checksum from generic RSS configure

Document what is "all L4".

> 
> And we should assume this is only apply for generic RSS configure but not for flow API.

I don't think so. IMHO, it should report all RSS capabilities
regardless generic vs flow API RSS action.

It is just RSS capabilities reporting w/o any context.

> 
> Because the rte_flow_validate is the recommended method to check if a RSS action is supported in flow API or not.

It could restrict the subset. But superset should be reported
in caps.

> 
>>
>>  * If I try to use it in default RSS config, but the request
>>    fail, it could be very confusing.
>>
>>  * Will it distribute TCP packets? UDP packets? SCTP packets?
>>    Or should I care about RSS for some of them based on other
>>    supported fields? E.g. if SCTP is not supported by the NIC,
>>    I need to install RSS flow rule for the IP protocol to do
>>    RSS based on IPv4/IPv6 addresses. But if SCTP is supported,
>>    I'm happy to use ETH_RSS_L4_CHKSUM for it as well.
>>
>>> In flow API, if no l4 protocol in pattern , the PMD should return
>>> failure (or maybe some default behavior), and I think this is not a
>>> new question as it happens all the cases
>>> e.g.:
>>> pattern eth / vlan / end action rss type ipv4 .
>>
>> IMHO, it would be pretty logical to apply RSS to IPv4 packets only and send
>> everything else to default queue.
> 
> Yes, this also make sense to me, but I think PMD's flow parser still can have more strict check, as it does not drop any feature that the NIC can support.
> 
>>
>>>>
>>>> Is UDP checksum 0 treated as no checksum and go to default queue or
>>>> treated as a regular checksum with value equal to 0?
>>>
>>> I think we can treat it as value 0, as least our hardware behavior like this, is
>> this any issue?
>>
>> OK, no problem. Just document it.
>>
>>>>
>>>> I tend to agree that 3 flags is too much for the feature, but one
>>>> flag without properly defined meaning is not good as well.
>>>>
>>>> I just want rules to be defined and documented.'
>>>
>>> Agree, we need more document for this. if you agree above proposal.
>>>
>