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Page 28 | AlliedWare Plus™ OS: Overview of QoS
Strict priority
scheduling
Then, to set queues to use strict priority scheduling, use the command:
priority-queue <queue-list>
Specify the queues as a space-separated list. For example, to put queues 3, 5, and 6 into the
strict-priority group of queues, use the command:
awplus(config-if)#priority-queue 3 5 6
Weighted
round robin
To put queues into one of the weighted round robin groups, use the command:
wrr-queue group <1-2> weight <6-255> queues <queue-list>
This configures a set of queues in the wrr
1
or wrr2 group of queues, and sets their weights in
that group. The weight specifies the number of bytes transmitted from the queue in
proportion to the values for other queues in the same wrr group. For example, a queue with
a weight of 30 would transmit twice as many bytes as a queue with a weight of
1
5.
To put queues 2 and 7 into the wrr
1
group, and give them a weight of 30 in that group, use
the command:
wrr-group 1 weight 30 queues 2 7
To put queue 5 into the wrr
1
group, and give it a weight of
1
5 in that group, use the
command:
awplus(config-if)#wrr-group 1 weight 15 queues 5
Egress rate
limits
It is also possible to set an egress rate limit on a queue, using the command:
wrr-queue egress-rate-limit <bandwidth> queues <queue-list>
You can specify bandwidth in kilobits (e.g. 2000 or 2000k), megabits (e.g. 2m), or gigabits (e.g.
2g).
Although this command begins with the keyword wrr-queue, you can use it to configure
queues that are members of the strict-priority group of queues.
For more information, see "Egress bandwidth limiting" on page 29.
Packet buffer
pool
Each port has a dedicated pool of packet buffers that the egress queues use for queuing
packets. Theoretically, any one of the queues on a given port could use up that port's whole
buffer pool, although there is a mechanism in place to prevent this. If the mechanism did not
exist, a single queue could use the whole buffer pool, for example, if a port were
oversubscribed by a high-bandwidth high-priority stream and a high-bandwidth low-priority
stream. The high-priority stream would get more access to the egress bandwidth than the
low-priority stream, so the queue holding the low-priority traffic would grow progressively
longer. In the end, the low-priority stream would consume the entire buffer pool on the port,
thereby starving the high-priority stream of any packet-queuing resource. This would be
highly undesirable.
To avoid this problem, there is a limit on the percentage of the available buffer pool that any
given queue can consume. By default, each queue is limited to
1
2%, but you can change this
by using the following command:
wrr-queue queue-limit <1-100> <1-100> <1-100> <1-100> <1-100> <1-100>
<1-100> <1-100>