Dell 53-1002116-01 manual Traffic class scheduling policy, SP0 SP1 SP2 SP3 SP4 SP5 SP6 SP8

Scheduling 10

Figure 8 describes the frame scheduling order for a WRR scheduler servicing two WRR queues. The higher numbered queue is considered higher priority (WRR2) and the weights indicate the network bandwidth should be allocated in a 2:1 ratio between the two queues. In Figure 8 WRR2 should receive 66 percent of bandwidth and WRR1 receives 33 percent. The WRR scheduler tracks the extra bandwidth used and subtracts it from the bandwidth allocation for the next cycle through the queues. In this way, the bandwidth utilization statistically matches the queue weights over longer time periods.

FIGURE 8 WRR schedule — two queues

Deficit Weighted Round Robin (DWRR) is an improved version of WRR. DWRR remembers the excess used when a queue goes over its bandwidth allocation and reduces the queue's bandwidth allocation in the subsequent rounds. This way the actual bandwidth usage is closer to the defined level when compared to WRR.

Traffic class scheduling policy

The traffic classes are numbered from 0 to 7; higher numbered traffic classes are considered higher priority. The Dell M8428-k provides full flexibility in controlling the number of SP-to-WRR queues. The number of SP queues is specified in N (SP1 through 8), then the highest priority traffic classes are configured for SP service and the remaining eight are WRR serviced. Table 20 describes the set of scheduling configurations supported.

When you configure the QoS queue to use strict priority 4 (SP4), then traffic class 7 will use SP4, traffic class 6 will use SP3, and so on down the list. You use the strict priority mappings to control how the different traffic classes will be routed in the queue.

TABLE 20	Supported scheduling configurations
Traffic Class	SP0	SP1	SP2	SP3	SP4	SP5	SP6	SP8
7	WRR8	SP1	SP2	SP3	SP4	SP5	SP6	SP8
6	WRR7	WRR7	SP1	SP2	SP3	SP4	SP5	SP7
5	WRR6	WRR6	WRR6	SP1	SP2	SP3	SP4	SP6
4	WRR5	WRR5	WRR5	WRR5	SP1	SP2	SP3	SP5
3	WRR4	WRR4	WRR4	WRR4	WRR4	SP1	SP2	SP4
2	WRR3	WRR3	WRR3	WRR3	WRR3	WRR3	SP1	SP3
1	WRR2	WRR2	WRR2	WRR2	WRR2	WRR2	WRR2	SP2
0	WRR1	WRR1	WRR1	WRR1	WRR1	WRR1	WRR1	SP1

Dell Converged Enhanced Ethernet Administrator’s Guide	105
53-1002116-01