Lenovo Flex System Fabric CN4093, Application Manual

Page: 225 / 634

© Copyright Lenovo 2017 Chapter 12: Quality of Service
225
Queuing and Scheduling
The CN4093 can be configured to have either 2 or 8 output Class of Service (COS)
queues per port, into which each packet is placed. Each packet’s 802.1p priority
determines its COS queue, except when an ACL action sets the COS queue of the
packet.
You can configure the following attributes for COS queues:
 Map 802.1p priority value to a COS queue
 Define the scheduling weight of each COS queue
You can map 802.1p priority value to a COS queue, as follows:
To set the COS queue scheduling weight, use the following command.
The scheduling weight can be set from 0 to 15. Weight values from 1 to 15 set the
queue to use weighted round ‐ robin (WRR) scheduling, which distributes larger
numbers of packets to queues with the highest weight values. For distribution
purposes, each packet is counted the same, regardless of the packet’s size.
A scheduling weight of 0 (zero) indicates strict priority. Traffic in strict priority
queue has precedence over other all queues. If more than one queue is assigned a
weight of 0, the strict queue with highest queue number will be served first. Once
all traffic in strict queues is delivered, any remaining bandwidth will be allocated
to the WRR queues, divided according to their weight values.
Note:
Use caution when assigning strict scheduling to queues. Heavy traffic in
queues assigned with a weight of 0 can starve lower priority queues.
For a scheduling method that uses a weighted deficit round ‐ robin (WDRR)
algorithm, distributing packets with an awareness of packet size, see “Enhanced
Transmission Selection” on page 352 .
CN 4093(config)# qos transmit-queue mapping
<priority value (0 ‐ 7)> <COS queue (0 ‐ 7)>
CN 4093(config)# qos transmit-queue weight-cos
<COSq number> <COSq weight (0 ‐ 15)>