[PATCH v3 1/2] examples/l3fwd: relax RSS requirement with option

[Konstantin Ananyev]

>> Now the port Rx mq_mode had been set to RTE_ETH_MQ_RX_RSS
>> by default, but some hw and/or virtual interface does not
>> support the RSS and offload mode presupposed, e.g., some
>> virtio interfaces in the cloud don't support
>> RSS and the error msg may like:
>> 
>> virtio_dev_configure(): RSS support requested but not supported by
>> the device
>> Port0 dev_configure = -95
>> 
>> So to enable the l3fwd running in that environment, the Rx mode requirement
>> can be relaxed to reflect the hardware feature reality here, and the l3fwd
>> can run smoothly then.
>> 
>> An option named "relax-rx-mode" is added to enable the relax action
>> here, and it's disabled by default.
>> 
>> Signed-off-by: Trevor Tao <mailto:taozj888 at 163.com>
>
>Doesn't need to be an option. The application can just look at the offload
>flags and quickly determine that if multiple queues are being used than
>RSS is required. If device doesn't support RSS, then fallback to single
>queue with a warning.
>
>Hi Stephen:
>
>I think the option here was suggested/required by Konstantin Ananyev <mailto:konstantin.v.ananyev at yandex.ru>.
>The discussion thread is listed below:
>
">>>>Should we probably instead have a new commnad-line option to explicitly 
>>>>disable RSS?
>>> 
>>>>Something like: '--no-rss' or so?
>>> Trevor: the RSS capability for a certain port was got by the rte_eth_dev_info_get() automatically, and we think the user should not care about its status beforehand, but if it's missing, a warning notification for the degrade here would be proposed to make it run smoothly.
>>
>>Personally, I still think it would be better the user will
>>have an ability to disable it explicitly.
>>Same as l3fwd does now with 'parse-ptype'.
>>
>
>[Morten]: The "relax-rx-mode" does not explicitly disable RSS, it enables the behavior Stephen suggested: If RSS is not supported by the device, fallback to single queue with a warning. We don't need an option >for this; it should be the default behavior.
>[Morten]: I think Konstantin was asking for an option "no-rss" (or "disable-rss") to force use of single queue (disable RSS), regardless if the device supports RSS or not.

Yes, that what was my initial suggestion: let people explicitly disable RSS if they want to.
BTW,  I think it wouldn't change number of HW queues in any way.
It would just disable distribution of packets among HW queues based on RSS.
Konstantin