[dpdk-dev] i40e and RSS woes

Vlad Zolotarov vladz at cloudius-systems.com
Mon Aug 24 20:26:17 CEST 2015

On 08/24/15 20:51, Zhang, Helin wrote:
>> -----Original Message-----
>> From: Vlad Zolotarov [mailto:vladz at cloudius-systems.com]
>> Sent: Monday, August 24, 2015 4:14 AM
>> To: Zhang, Helin; Gleb Natapov; dev at dpdk.org
>> Subject: Re: [dpdk-dev] i40e and RSS woes
>> On 03/05/15 07:56, Zhang, Helin wrote:
>>> Hi Gleb
>>> Sorry for late! I am struggling on my tasks for the following DPDK release these
>> days.
>>>> -----Original Message-----
>>>> From: Gleb Natapov [mailto:gleb at cloudius-systems.com]
>>>> Sent: Monday, March 2, 2015 8:56 PM
>>>> To: dev at dpdk.org
>>>> Cc: Zhang, Helin
>>>> Subject: Re: i40e and RSS woes
>>>> Ping.
>>>> On Thu, Feb 19, 2015 at 04:50:10PM +0200, Gleb Natapov wrote:
>>>>> CCing i40e driver author in a hope to get an answer.
>>>>> On Mon, Feb 16, 2015 at 03:36:54PM +0200, Gleb Natapov wrote:
>>>>>> I have an application that works reasonably well with ixgbe driver,
>>>>>> but when I try to use it with i40e I encounter various RSS related issues.
>>>>>> First one is that for some reason i40e, when it builds default reta
>>>>>> table, round down number of queues to power of two. Why is this? If
>>> It seems because of i40e queue configuration. We will check it more
>>> and see if it can be changed or improved later.
>> Helin, hi!
>> Sorry for bringing it back but it seems that the RSS queues number issue
>> (rounding it down to the nearest power of 2) still hasn't been addressed in the
>> master branch.
>> Could u, pls., clarify what is that "i40e queue configuration" that requires this
>> alignment u are referring above?
>>   From what i could see "num" parameter is not propagated outside the
>> i40e_pf_config_rss() in any form except for RSS table contents.
>> This means that any code that would need to know the number of Rx queues
>> would use the dev_data->nb_rx_queues (e.g. i40e_dev_rx_init()) and wouldn't
>> be able to know that i40e_pf_config_rss() something different except for
>> scanning the RSS table in HW which is of course not an option.
>> Therefore, from the first look it seems that this rounding may be safely removed
>> unless I've missed something.
> Could you help to refer to the data sheet of 'Hash Filter', 'Receive Queue Regions', it
> is said that '1, 2, 4, 8, 16, 32, 64' are the supported queue regions.
> Yes, we should support more than 64 queues per port, but for rss, it should be one
> of '1, 2, 4, 8, 16, 32, 64'.

"The VSIs support 8 regions of receive queues that are aimed mainly for
the TCs. The TC regions are defined per VSI by the VSIQF_TCREGION
register. The region sizes (defined by the TC_SIZE fields) can be any of
the following value: 1, 2, 4, 8, 16, 32, 64 as long as the total number of
queues do not exceed the VSI allocation. These regions starts at the
offset defined by the TC_OFFSET parameter. According to the region
size, the ‘n’ LS bits of the Queue Index from the LUT are enabled."

I think the above says that the region sizes may only be one of the 
mentioned values.

AFAIU this doesn't mean that the number or RSS queues has to be the same 
- it may not exceed it.

Just like it's stated in the "Outcome Queue Index" definition the final 
mapping to the PF index space is done using the
VSILAN_QTABLE or VSILAN_QBASE registers (a.k.a. RSS indirection table).

For instance if u have a region of size 8 u may configure 3 RSS queues 
by setting the following RSS table:

> Thanks,
> Helin
>> Pls., comment.
>> thanks,
>> vlad
>>>>>> I configure reta by my own using all of the queues everything seams
>>>>>> to be working. To add insult to injury I do not get any errors
>>>>>> during configuration some queues just do not receive any traffic.
>>>>>> The second problem is that for some reason i40e does not use 40
>>>>>> byte toeplitz hash key like any other driver, but it expects the
>>>>>> key to be 52 bytes. And it would have being fine (if we ignore the
>>>>>> fact that it contradicts MS spec), but how my high level code
>>>>>> suppose to know
>>>> that?
>>> Actually a rss_key_len was introduced in struct rte_eth_rss_conf
>>> recently. So the length should be indicated clearly. But I found the
>>> annotations of that structure should have been reworked. I will try to rework it
>> with clear descriptions.
>>>>>> And again, device configuration does not fail when wrong key length
>>>>>> is provided, it just uses some other key. Guys this kind of error
>>>>>> handling is completely unacceptable.
>>> If less length of key is provided, it will not be used at all, the default key will be
>> used.
>>> So there is no issue as you said. But we need to add more clear
>>> description for the structure of rte_eth_rss_conf.
>>> Thank you very much for the good comments!
>>> Regards,
>>> Helin
>>>>>> The last one is more of a question. Why interface to change RSS
>>>>>> hash function (XOR or toeplitz) is part of a filter configuration
>>>>>> and not rss config?
>>>>>> --
>>>>>> 			Gleb.
>>>>> --
>>>>> 			Gleb.
>>>> --
>>>> 			Gleb.

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