Brocade Communications Systems 53-1001761-01 Manual De Usuario
Converged Enhanced Ethernet Administrator’s Guide
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53-1001761-01
Scheduling
9
DRAFT: BROCADE CONFIDENTIAL
describes the frame scheduling order for an SP scheduler servicing two SP queues. The
higher numbered queue, SP2, has a higher priority.
FIGURE 10
Strict priority schedule — two queues
Deficit weighted round robin scheduling
Weighted Round Robin (WRR) 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.
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.
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
network bandwidth should be allocated in a 2:1 ratio between the two queues. In
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.
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 11
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.
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 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 eight are WRR serviced.
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 eight are WRR serviced.
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.
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.