Queuing And Scheduling - IBM RackSwitch G8000 Application Manual

Queuing and Scheduling

© Copyright IBM Corp. 2011
The G8000 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.
Note: In stacking mode, because one COS queue is reserved for internal use, the
number of configurable COS queues is either 1 or 7.
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:
RS G8000(config)# qos transmit-queue mapping <802.1p priority value (0-7)>
<COS queue (0-7)>
To set the COS queue scheduling weight, use the following command.
RS G8000(config)# qos transmit-queue weight-cos <COSq number>
<COSq weight (0-15)>
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.
Chapter 11. Quality of Service
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