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118 Converged Enhanced Ethernet Administrator’s Guide
53-1002163-02
Scheduling
11
DRAFT: BROCADE CONFIDENTIAL
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. Fabric OS v7.0.0 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 27
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.
Figure 10 shows that extending the frame scheduler to a hybrid SP+WRR system is fairly
straightforward. All SP queues are considered strictly higher priority than WRR so they are serviced
first. Once all SP queues are drained, then the normal WRR scheduling behavior is applied to the
non-empty WRR queues.
FIGURE 10 Strict priority and Weighted Round Robin scheduler
Scheduling the QoS queue
To specify the schedule to use, perform the following steps from privileged EXEC mode.
1. Enter global configuration mode.
switch#configure terminal
TABLE 27 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