Brocade Converged Enhanced Ethernet Administrator's Guide v6.1.2_cee (53-1001258-01, June 2009)

Converged Enhanced Ethernet Administrator’s Guide 115
53-1001258-01
Scheduling
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Figure 9 shows the packet scheduling order for a SP scheduler servicing two SP queues. The higher
numbered queue, SP2, has a higher priority.
FIGURE 9 Strict priority schedule — two queues
Weighted round robin scheduling
Weighted round robin scheduling is used to facilitate controlled sharing of the network bandwidth.
WRR assigns a weight to each queue; that value is then used to determine the amount of
bandwidth allocated to the queue. The round robin aspect of the scheduling allows each queue to
be serviced in a set ordering, sending a limited amount of data before moving onto the next queue
and cycling back to the highest priority queue after the lowest priority is serviced.
Figure 10 shows the packet 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 10 WRR2 should
receive 66% of bandwidth and WRR1 receives 33%. The WRR scheduler tracks the extra
bandwidth used and subtracts it from the bandwidth allocation for the next cycle through the
queues. In this the bandwidth utilization statistically matches the queue weights over longer time
periods.
FIGURE 10 WRR schedule — two queues
Traffic class scheduling policy
The traffic classes are numbered from 0 to 7; higher numbered traffic classes are considered
higher priority. The Brocade 8000 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 8 are WRR serviced. Table 20 shows the
set of scheduling configurations supported.