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

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

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").
>
>>>>> +	RTE_ETH_HASH_FUNCTION_SYMMETRIC_TOEPLITZ_SORT,
>>>>>     	RTE_ETH_HASH_FUNCTION_MAX,
>>>>>     };
>>>>>