Dell Mellanox Family of Adapters - Manual (Page 27)

User Manual for Mellanox ConnectX®-3 10/40 Gigabit Ethernet Adapters for Dell PowerEdge Servers Rev 1.1
Mellanox Technologies 27
4.2.3.3 RoCE Quality of Service Mapping
Applications use RDMA-CM API to create and use QPs.
The following is the RoCE QoS mapping flow:
1. The application sets the ToS of the QP using the rdma_set_option option
( RDMA_OPTION_ID_TOS , value).
2. ToS is translated into the Socket Priority ( sk_prio ) using a fixed translation:
3. The Socket Priority is mapped to the User Priority (UP) using the tc command.
In case of a VLAN device, the parent real device is used for the purpose of this mapping.
4. The the UP is mapped to the TC as configured by the mlnx_qos tool or by the lldpad daemon
if DCBX is used.
4.2.3.4 Raw Ethernet QP Quality of Service Mapping
Applications open a Raw Ethernet QP using VERBs directly.
The following is the RoCE QoS mapping flow:
1. The application sets the UP of the Raw Ethernet QP during the INIT to RTR state transition of
the QP:
• Sets qp_attrs.ah_attrs.sl = up
• Calls modify_qp with IB_QP_AV set in the mask
2. The UP is mapped to the TC as configured by the mlnx_qos tool or by the lldpad daemon if
DCBX is used
4.2.3.5 Map Priorities with tc_wrap.py/mlnx_qos
Network flow that can be managed by QoS attributes is described by a User Priority (UP). A
user's
sk_prio is mapped to UP which in turn is mapped into TC.
• Indicating the UP
TOS 0 <=> sk_prio 0
TOS 8 <=> sk_prio 2
TOS 24 <=> sk_prio 4
TOS 16 <=> sk_prio 6
With RoCE, there can only be 4 predefined ToS values for the purpose of QoS mapping.
When using Raw Ethernet QP mapping, the TOS/sk_prio to UP mapping is lost.
Performing the Raw Ethernet QP mapping forces the QP to transmit using the given UP.
If packets with VLAN tag are transmitted, UP in the VLAN tag will be overwritten with
the given UP.