Dell MX9116n EMC SmartFabric OS10 User Guide Release 10.5.0 - Page 1162

Consider the example where you have configured WDRR and shaping on a queue that has two different traffic streams, TS1 and TS2, that uses preamble, SFD, and IFG overhead fields: • If the IFG in TS1 uses 16 bytes, QoS rate adjust value should be 24 (preamble + SFD requires 8 bytes and IFG 16 bytes). • If the IFG in TS2 uses 12 bytes, QoS rate adjust value should be 20 (preamble + SFD requires 8 bytes and IFG 12 bytes). In this case, the highest QoS rate adjust value between the two streams is 24 bytes. Hence, you must configure the QoS rate adjust value as 24. NOTE: This feature is not supported on the S4200-ON Series platforms. Buffer management OS10 devices distribute the total available buffer resources into two buffer pools at ingress direction and three buffer pools at egress direction of all physical ports. You can map a single traffic class or a group of traffic classes to a priority group. All ports in a system are allocated a certain amount of buffers from corresponding pools based on the configuration state of each priority-group or queue. The remaining buffers in the pool are shared across all similarly configured ports. The following buffer pools are available: • Ingress buffer pools: ○ Lossy pool (default) ○ Lossless pool ▪ PFC-For all platforms ▪ LLFC-For all platforms except the S4200-ON series switches • Egress buffer pools: ○ Lossy pool (default) ○ Lossless pool ▪ PFC-For all platforms ▪ LLFC-For all platforms except the S4200-ON series switches ○ CPU pool (CPU control traffic) The following terms are used in this section: • Default buffer-By default, the system allocates a certain amount of default buffer to all the ports. • Reserved buffer-The system reserves a dedicated amount of buffer to a port or a priority group (at ingress) and a port or a queue (at egress). • Shared buffer-Is the total available buffer space minus the reserved buffer space. Shared buffer is used for CPU control traffic and is dynamically allocated to the ports when memory space is needed. • Alpha value- • Xoff threshold (transmit off)-When the system reaches the Xoff threshold, to prevent traffic loss, the system pauses and does not accept any further packets. • Xon threshold (transmit on)-When the system reaches the Xon threshold, the system resumes and accepts the packets. For example, when all ports are allocated as reserved buffers from the lossy (default) pool, the remaining buffers in the lossy pool are shared across all ports, except the CPU port. When you enable priority flow control (PFC) on the ports, all the PFC-enabled queues and priority-groups use the buffers from the lossless pool. You must use the network QoS policy type to configure PFC on the ports. OS10 dedicates a separate buffer pool for CPU traffic. All default reserved buffers for the CPU port queues are from the CPU pool. The remaining buffers are shared across all CPU queues. You can modify the buffer settings of CPU queues. You can configure the size of the CPU pool using the control-plane-buffer-size command. OS10 allows configuration of buffers per priority-group and queue for each port. Buffer-usage accounting happens for ingress packets on ingress pools and egress packets on egress pool. You can configure ingresspacket buffer accounting per priority-group and egress-packet buffer accounting per queue level. 1162 Quality of service