Re: [PATCH v2 1/2] ethdev: add new symmetric hash function

["lihuisong (C)" <lihuisong@huawei.com>]

在 2023/8/31 14:25, Xueming(Steven) Li 写道:
>
>> -----Original Message-----
>> From: lihuisong (C) <lihuisong@huawei.com>
>> Sent: 8/31/2023 9:24
>> To: Xueming(Steven) Li <xuemingl@nvidia.com>; Ori Kam <orika@nvidia.com>
>> Cc: dev@dpdk.org; fengchengwen@huawei.com; Ivan Malov
>> <ivan.malov@arknetworks.am>
>> Subject: Re: [PATCH v2 1/2] ethdev: add new symmetric hash function
>>
>>
>> 在 2023/8/30 21:09, Xueming(Steven) Li 写道:
>>>> -----Original Message-----
>>>> From: lihuisong (C) <lihuisong@huawei.com>
>>>> Sent: 8/30/2023 20:42
>>>> To: Xueming(Steven) Li <xuemingl@nvidia.com>; Ori Kam
>>>> <orika@nvidia.com>
>>>> Cc: dev@dpdk.org; fengchengwen@huawei.com; Ivan Malov
>>>> <ivan.malov@arknetworks.am>
>>>> Subject: Re: [PATCH v2 1/2] ethdev: add new symmetric hash function
>>>>
>>>>
>>>> 在 2023/8/30 16:38, Xueming(Steven) Li 写道:
>>>>>> -----Original Message-----
>>>>>> From: lihuisong (C) <lihuisong@huawei.com>
>>>>>> Sent: 8/30/2023 15:51
>>>>>> To: Xueming(Steven) Li <xuemingl@nvidia.com>; Ori Kam
>>>>>> <orika@nvidia.com>
>>>>>> Cc: dev@dpdk.org; fengchengwen@huawei.com; Ivan Malov
>>>>>> <ivan.malov@arknetworks.am>
>>>>>> Subject: Re: [PATCH v2 1/2] ethdev: add new symmetric hash function
>>>>>>
>>>>>> Hi Xueming,
>>>>>>
>>>>>> 在 2023/8/27 16:17, Xueming Li 写道:
>>>>>>> The new symmetric hash function swap src/dst L3 address and
>>>>>>> L4 ports automatically by sorting.
>>>>>>>
>>>>>>> Signed-off-by: Xueming Li <xuemingl@nvidia.com>
>>>>>>> ---
>>>>>>>      lib/ethdev/rte_flow.h | 7 +++++++
>>>>>>>      1 file changed, 7 insertions(+)
>>>>>>>
>>>>>>> diff --git a/lib/ethdev/rte_flow.h b/lib/ethdev/rte_flow.h index
>>>>>>> 2ebb76dbc0..4f4421ca50 100644
>>>>>>> --- a/lib/ethdev/rte_flow.h
>>>>>>> +++ b/lib/ethdev/rte_flow.h
>>>>>>> @@ -3196,6 +3196,13 @@ enum rte_eth_hash_function {
>>>>>>>      	 * src or dst address will xor with zero pair.
>>>>>>>      	 */
>>>>>>>      	RTE_ETH_HASH_FUNCTION_SYMMETRIC_TOEPLITZ,
>>>>>>> +	/**
>>>>>>> +	 * Symmetric Toeplitz: L3 and L4 fields are sorted prior to
>>>>>>> +	 * the hash function.
>>>>>>> +	 *  If src_ip > dst_ip, swap src_ip and dst_ip.
>>>>>>> +	 *  If src_port > dst_port, swap src_port and dst_port.
>>>>>>> +	 */
>>>>>> If hash result are computed by the order:
>>>> "src_ip+dst_ip+src_port+dst_port"
>>>>>> How to obtain the value of every L3 and L4 field obove?
>>>>>> I still cannot understand how to swap and set these values for these
>> fields?
>>>>> Hash result is computed by order ""src_ip+dst_ip+src_port+dst_port"
>>>>> Here is a detailed explanation of standard hash and symmetric hash by
>> key:
>>>>>      https://www.ndsl.kaist.edu/~kyoungsoo/papers/TR-symRSS.pdf
>>>>>
>>>>> If src_ip > dst_ip, swap them, then the input becomes:
>>>>>      "dst_ip+src_ip+src_port+dst_port" // please note src and dst IP
>>>>> are
>>>> swapped.
>>>>> Same for L4 ports.
>>>> get it.
>>>> What are the advantages of the symmetric toeplitz sort?
>>>> Or why swap here?
>>> It's a different symmetric hash calculation, hardware can support either/all
>> of them.
>>>   From calculation perspective, the hash result distribution is better,
>>> the result is more suitable to be used as hash table key.
>> I get it now.
>> but I have a question.
>> why not is that if src_ip < dst_ip, then swap src_ip and dst_ip?
>> I guess this is going to have the same effect as you said, right?
>> The symmetric toeplitz sort is not a standard algorithm, is just to enhance the
>> hash result distribution.
>> If what I understand is right,
>> it is better that the new RSS algorithm should works on the one of them
>> ("src_ip > dst_ip" or "src_ip < dst_ip").
> Any special reason to introduce the descending sort?
Because the descending sort also can achieve the goal.
After all, this doesn't seem like a standard algorithm.

> I personally prefer to keep the enum clean unless some new hw or new algorithm introduced.

Agree with you. But this new enum cannot reveal ascending or descending 
sort.

>
>>>>>>> +	RTE_ETH_HASH_FUNCTION_SYMMETRIC_TOEPLITZ_SORT,
>>>>>>>      	RTE_ETH_HASH_FUNCTION_MAX,
>>>>>>>      };
>>>>>>>