Service Egress and Ingress QoS Policies
Quality of Service Guide 369
Pool-per-queue WRED
When the wred-queue mode pool-per-queue command is defined and the queue ID is created on FP2
or higher based hardware, a buffer pool is created specifically for the queue and the queue obtains all
buffers from that pool. The size of the pool is the same as the size of the queue. In this manner, the
WRED slopes that operate based on the pool’s buffer utilization are also reacting to the congestion
depth of the queue.
The size of the buffer pool is dictated by the queue’s mbs parameter. The size of the reserved CBS
portion of the buffer pool is dictated by the queue’s cbs parameter. The provisioning characteristics of
the mbs and cbs commands are not changed.
In the case where this is applied on FP2 or higher based hardware which has WRED queue support
shutdown (config>card>fp>egress>wred-queue-control>shutdown) the queue will continue to map
to either to its default pool or the pool defined in the pool command. If the no shutdown command is
executed in the wred-queue-control context, the queue will at that point be automatically moved to
its own WRED pool.
Each pool created for a queue using the wred-queue command shares buffers with all other wred-
queue enabled queues on the same forwarding plane. The WRED pool buffer management behavior
is defined within the config>card>fp>egress>wred-queue-control CLI context.
The WRED slopes within the pool are defined by the slope policy associated with the queue. When a
policy is not explicitly defined, the default slope policy is used. The slope policy enables, disables and
defines the relative geometry of the high, low, and exceed WRED slopes in the pool. The policy also
specifies the time average factor used by the pool when calculating the weighted average pool depth.
As packets attempt to enter the egress queue, they are associated with the high, low, or exceed WRED
slope based on the packets’ profile. If the packet is in-profile, the high slope is used. If the packet is
out-of-profile, the low slope is used, and, if the packet is exceed-profile, then exceed slope is used. This
mapping of packet profile to slope is enabled using the slope-usage default parameter. Each WRED
slope performs a probability discard based on the current weighted average pool depth.
When wred-queue is enabled for a SAP egress queue on FP2 or higher based hardware, the queue pool
hi-low-prio-only and hi-prio-only commands are ignored; traffic mapped to a slope which is
shutdown will use the MBS drop tail.
The configuration of wred-queue mode pool-per-queue is ignored on FP1 hardware. The resource
usage for the wred-queue pool-per-queue per forwarding plane can be seen in the tools dump
resource-usage card [slot-num] fp [fp-number] output under Dynamic Q2 Wred Pools.
The no form of the command restores the generic buffer pool behavior to the queue. The WRED pool
is removed from the system. The queue will be moved to either the default buffer pool or to a named
pool if defined and the pool exists. The queue then uses the default congestion control behavior.
Default no wred-queue
Parameters slope-policy-name — Specifies an existing slope policy that is used to override the default WRED
slope policy.
To Next Page
Loading...
