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

["Xueming(Steven) Li" <xuemingl@nvidia.com>]

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

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