Re: [RFC v2] RoCE v2.0 Entropy - IPv6 Flow Label and UDP Source Port

[Mark Zhang <markz@mellanox.com>]

On 1/8/2020 10:26 PM, Alex Rosenbaum wrote:
> A combination of the flow_label field in the IPv6 header and UDP source port
> field in RoCE v2.0 are used to identify a group of packets that must be
> delivered in order by the network, end-to-end.
> These fields are used to create entropy for network routers (ECMP), load
> balancers and 802.3ad link aggregation switching that are not aware of RoCE IB
> headers.
> 
> The flow_label field is defined by a 20 bit hash value. CM based connections
> will use a hash function definition based on the service type (QP Type) and
> Service ID (SID). Where CM services are not used, the 20 bit hash will be
> according to the source and destination QPN values.
> Drivers will derive the RoCE v2.0 UDP src_port from the flow_label result.
> 
> UDP source port selection must adhere IANA port allocation ranges. Thus we will
> be using IANA recommendation for Ephemeral port range of: 49152-65535, or in
> hex: 0xC000-0xFFFF.
> 
> The below calculations take into account the importance of producing a symmetric
> hash result so we can support symmetric hash calculation of network elements.
> 
> Hash Calculation for RDMA IP CM Service
> =======================================
> For RDMA IP CM Services, based on QP1 iMAD usage and connected RC QPs using the
> RDMA IP CM Service ID, the flow label will be calculated according to IBTA CM
> REQ private data info and Service ID.
> 
> Flow label hash function calculations definition will be defined as:
> Extract the following fields from the CM IP REQ:
>    CM_REQ.ServiceID.DstPort [2 Bytes]
>    CM_REQ.PrivateData.SrcPort [2 Bytes]
>    u32 hash = DstPort * SrcPort;
>    hash ^= (hash >> 16);
>    hash ^= (hash >> 8);
>    AH_ATTR.GRH.flow_label = hash AND IB_GRH_FLOWLABEL_MASK;
> 
>    #define IB_GRH_FLOWLABEL_MASK  0x000FFFFF
> 
> Result of the above hash will be kept in the CM's route path record connection
> context and will be used all across its vitality for all preceding CM messages
> on both ends of the connection (including REP, REJ, DREQ, DREP, ..).
> Once connection is established, the corresponding Connected RC QPs, on both
> ends of the connection, will update their context with the calculated RDMA IP
> CM Service based flow_label and UDP src_port values at the Connect phase of
> the active side and Accept phase of the passive side of the connection.
> 
> CM will provide to the calculated value of the flow_label hash (20 bit) result
> in the 'uint32_t flow_label' field of 'struct ibv_global_route' in 'struct
> ibv_ah_attr'.
> The 'struct ibv_ah_attr' is passed by the CM to the provider library when
> modifying a connected QP's (e.g.: RC) state by calling 'ibv_modify_qp(qp,
> ah_attr, attr_mask |= IBV_QP_AV)' or when create a AH for working with
> datagram QP's (e.g.: UD) by calling ibv_create_ah(ah_attr).
> 
> Hash Calculation for non-RDMA CM Service ID
> ===========================================
> For non CM QP's, the application can define the flow_label value in the
> 'struct ibv_ah_attr' when modifying the connected QP's (e.g.: RC) or creating
> a AH for the datagram QP's (e.g.: UD).
> 

Hi Alex, when creating an AH for the datagram QP, I think we don't have 
the src.QP and dst.QP, so we can't set the flow_label here?


> If the provided flow_label value is zero, not set by the application (e.g.:
> legacy cases), then verbs providers should use the src.QP[24bit] and
> dst.QP[24bit] as input arguments for flow_label calculation.
> As QPN's are an array of 3 bytes, the multiplication will result in 6 bytes
> value. We'll define a flow_label value as:
>    DstQPn [3 Bytes]
>    SrcQPn [3 Bytes]
>    u64 hash = DstQPn * SrcQPn;
>    hash ^= (hash >> 20);
>    hash ^= (hash >> 40);
>    AH_ATTR.GRH.flow_label = hash AND IB_GRH_FLOWLABEL_MASK;
> 
> Hash Calculation for UDP src_port
> =================================
> Providers supporting RoCEv2 will use the 'flow_label' value as input to
> calculate the RoCEv2 UDP src_port, which will be used in the QP context or the
> AH context.
> 
> UDP src_port calculations from flow label:
> [while considering the 14 bits UDP port range according to IANA recommendation]
>    AH_ATTR.GRH.flow_label [20 bits]
>    u32 fl_low  = fl & 0x03FFF;
>    u32 fl_high = fl & 0xFC000;
>    u16 udp_sport = fl_low XOR (fl_high >> 14);
>    RoCE.UDP.src_port = udp_sport OR IB_ROCE_UDP_ENCAP_VALID_PORT
> 
>    #define IB_ROCE_UDP_ENCAP_VALID_PORT 0xC000
> 
> This is a v2 follow-up on "[RFC] RoCE v2.0 UDP Source Port Entropy" [1]
> 
> [1] https://www.spinics.net/lists/linux-rdma/msg73735.html
> 
> Signed-off-by: Alex Rosenbaum <alexr@mellanox.com>
>