Dell Mellanox Family of Adapters - Manual (Page 26)

Driver Installation and Configuration Rev 1.1
Mellanox Technologies 26
The following is the general mapping traffic to Traffic Classes flow:
1. The application sets the required Type of Service (ToS).
2. The ToS is translated into a Socket Priority ( sk_prio ).
3. The sk_prio is mapped to a User Priority (UP) by the system administrator (some applica-
tions set sk_prio directly).
4. The UP is mapped to TC by the network/system administrator.
5. TCs hold the actual QoS parameters
QoS can be applied on the following types of traffic. However, the general QoS flow may vary
among them:
• Plain Ethernet - Applications use regular inet sockets and the traffic passes via the ker-
nel Ethernet driver
• RoCE - Applications use the RDMA API to transmit using QPs
• Raw Ethernet QP - Application use VERBs API to transmit using a Raw Ethernet QP
4.2.3.2 Plain Ethernet Quality of Service Mapping
Applications use regular inet sockets and the traffic passes via the kernel Ethernet driver.
The following is the Plain Ethernet QoS mapping flow:
1. The application sets the ToS of the socket using setsockopt ( IP_TOS , value).
2. ToS is translated into the sk_prio using a fixed translation:
3. The Socket Priority is mapped to the UP:
• If the underlying device is a VLAN device, egress_map is used controlled by the vconfig
command. This is per VLAN mapping.
• If the underlying device is not a VLAN device, the tc command is used. In this case, even
though tc manual states that the mapping is from the sk_prio to the TC number, the
mlx4_en driver interprets this as a sk_prio to UP mapping.
Mapping the sk_prio to the UP is done by using tc_wrap.py -i -u
0,1,2,3,4,5,6,7
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.
TOS 0 <=> sk_prio 0
TOS 8 <=> sk_prio 2
TOS 24 <=> sk_prio 4
TOS 16 <=> sk_prio 6
Socket applications can use setsockopt ( SK_PRIO , value) to directly set the sk_prio
of the socket. In this case the ToS to sk_prio fixed mapping is not needed. This allows
the application and the administrator to utilize more than the 4 values possible via ToS.
In case of VLAN interface, the UP obtained according to the above mapping is also used
in the VLAN tag of the traffic