Re: [dpdk-dev] [PATCH v2] doc: update RSS action with best effort

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

On 8/5/2020 3:08 PM, Ori Kam wrote:
> Hi Andrew,
> 
>> -----Original Message-----
>> From: Andrew Rybchenko <arybchenko@solarflare.com>
>>
>> On 8/4/20 11:13 AM, Ori Kam wrote:
>>> Using the rte_flow action RSS types field,
>>> may result in undefined outcome.
>>>
>>> For example selecting both UDP and TCP,
>>> selecting TCP RSS type but the pattern is targeting UDP traffic.
>>> another option is that the PMD doesn't support all requested types.
>>>
>>> Until now, it wasn't clear what will happen in such cases.
>>> This commit clarify this issue by stating that the PMD
>>> will work in the best-effort mode.
>>>
>>> Signed-off-by: Ori Kam <orika@mellanox.com>
>>> ---
>>> v2:
>>>  * Based on ML, update that using only unsupported hash type
>>>    may cause the flow to be rejected by PMD.
>>> ---
>>>  doc/guides/prog_guide/rte_flow.rst | 11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>
>>> diff --git a/doc/guides/prog_guide/rte_flow.rst
>> b/doc/guides/prog_guide/rte_flow.rst
>>> index 3e5cd1e..d730b66 100644
>>> --- a/doc/guides/prog_guide/rte_flow.rst
>>> +++ b/doc/guides/prog_guide/rte_flow.rst
>>> @@ -1735,6 +1735,17 @@ unspecified "best-effort" settings from the
>> underlying PMD, which depending
>>>  on the flow rule, may result in anything ranging from empty (single queue)
>>>  to all-inclusive RSS.
>>>
>>> +Best effort will be used, in case there is a conflict inside the rule.
>>> +The conflict can be the result of:
>>> +
>>> +- Conflicting RSS types, for example setting both UDP and TCP.
>>
>> Thinking more about it, I see no conflict at all. It is common
>> to specify both TCP and UDP in hash function if user wants to
>> take TCP ports for TCP packets and UDP ports for UDP into
>> account.
>>
> I fully agree with you that it is common to use both UDP and TCP and
> expect it to work based on the traffic. this is the point of this patch.
> To clarify that this is valid input and the PMD will work in best effort mode.
> 

I think confusion occurs when the the RSS hash function set part of flow
rule rss action.
Than providing a UDP flow and setting UDP & TCP RSS hash types looks
confusing/wrong.

Does mlx support selecting hash function per flow?
Can it be possible to set RSS functions separately from any specific flow?

>
>>> +
>>> +- Conflicting between RSS types and the requested pattern to match,
>>> +  for example matching on UDP and hashing RSS on TCP.
>>
>> I'd not name it a conflict either. It is just common rule when
>> applicable fields are used only.
>>
> Just like my comment from above.
> 
>>> +
>>> +If requested RSS hash type is not supported,
>>> +and no supported hash type is requested then the PMD may reject the flow.
>>> +
>>
>> I disagree with such description. If requested RSS hash type is
>> not supported (not present in dev_info.flow_type_rss_offloads),
>> it must be rejected and error returned.
>> If requested RSS hash type is not supported for a packet
>> matching the rule, but supported in general (present in
>> dev_info.flow_type_rss_offloads), part of RSS hash type
>> specification may be ignored and only applicable bits are used.
>> If result is empty, PMD may reject the flow rule.
>>
> The flow should be rejected even if it is used with some type that is supported?
> 
> 
>>>  Note: RSS hash result is stored in the ``hash.rss`` mbuf field which
>>>  overlaps ``hash.fdir.lo``. Since `Action: MARK`_ sets the ``hash.fdir.hi``
>>>  field only, both can be requested simultaneously.
>>>
>