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: 8/30/2023 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.

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