[dpdk-dev] [PATCH v6 1/5] ethdev: introduce shared Rx queue

[Andrew Rybchenko]

On 10/15/21 1:54 PM, Xueming(Steven) Li wrote:
> On Fri, 2021-10-15 at 12:28 +0300, Andrew Rybchenko wrote:
>> On 10/12/21 5:39 PM, Xueming Li wrote:
>>> In current DPDK framework, each Rx queue is pre-loaded with mbufs to
>>> save incoming packets. For some PMDs, when number of representors scale
>>> out in a switch domain, the memory consumption became significant.
>>> Polling all ports also leads to high cache miss, high latency and low
>>> throughput.
>>>
>>> This patch introduce shared Rx queue. Ports in same Rx domain and
>>> switch domain could share Rx queue set by specifying non-zero sharing
>>> group in Rx queue configuration.
>>>
>>> No special API is defined to receive packets from shared Rx queue.
>>> Polling any member port of a shared Rx queue receives packets of that
>>> queue for all member ports, source port is identified by mbuf->port.
>>>
>>> Shared Rx queue must be polled in same thread or core, polling a queue
>>> ID of any member port is essentially same.
>>>
>>> Multiple share groups are supported by non-zero share group ID. Device
>>
>> "by non-zero share group ID" is not required. Since it must be
>> always non-zero to enable sharing.
>>
>>> should support mixed configuration by allowing multiple share
>>> groups and non-shared Rx queue.
>>>
>>> Even Rx queue shared, queue configuration like offloads and RSS should
>>> not be impacted.
>>
>> I don't understand above sentence.
>> Even when Rx queues are shared, queue configuration like
>> offloads and RSS may differ. If a PMD has some limitation,
>> it should care about consistency itself. These limitations
>> should be documented in the PMD documentation.
>>
> 
> OK, I'll remove this line.
> 
>>>
>>> Example grouping and polling model to reflect service priority:
>>>  Group1, 2 shared Rx queues per port: PF, rep0, rep1
>>>  Group2, 1 shared Rx queue per port: rep2, rep3, ... rep127
>>>  Core0: poll PF queue0
>>>  Core1: poll PF queue1
>>>  Core2: poll rep2 queue0
>>
>>
>> Can I have:
>> PF RxQ#0, RxQ#1
>> Rep0 RxQ#0 shared with PF RxQ#0
>> Rep1 RxQ#0 shared with PF RxQ#1
>>
>> I guess no, since it looks like RxQ ID must be equal.
>> Or am I missing something? Otherwise grouping rules
>> are not obvious to me. May be we need dedicated
>> shared_qid in boundaries of the share_group?
> 
> Yes, RxQ ID must be equal, following configuration should work:
>   Rep1 RxQ#1 shared with PF RxQ#1

But I want just one RxQ on Rep1. I don't need two.

> Equal mapping should work by default instead of a new field that must
> be set. I'll add some description to emphasis, how do you think?

Sorry for delay with reply. I think that above limitation is
not nice. It is better to avoid it.

[snip]