Znyx Networks bh5700 - Manual (Page 122)

In tc, the prio queuing discipline establishes multiple queues and specifies their associated
priority map. Although WRR support is not part of the standard tc distribution, it has been
added to the prio disciplinE.
The following example illustrates WRR. A strict priority scheduler is a simpler case that can be
constructed easily from this example.
Examine the existing CoS settings on the switch, noting the number of queues per port, queue
sizes, scheduling parameters, and priority map. Each of these values changes with this test.
The full set of commands to install four queues, a priority map, and weights is as follows:
tc qdisc add dev zhp0 handle 100:0 root prio bands 4 priomap 1 2 2 2
3 3 3 3 1 1 1 1 1 1 1 1 wrr 1 2 4 6
tc qdisc add dev zhp0 parent 100:1 pfifo limit 120
tc qdisc add dev zhp0 parent 100:2 pfifo limit 100
tc qdisc add dev zhp0 parent 100:3 pfifo limit 80
tc qdisc add dev zhp0 parent 100:4 pfifo limit 60
The first command attaches a queuing discipline as the root discipline for zhp0, with a handle of
“100:0,” as in the FIFO cases. The “prio” option identifies the type of queuing discipline.
Priority scheduling implies multiple queues and the “bands 4” parameters specify that there are
four queues.
The priority map may be read from left to right as Priority n maps to Queue q, where
n is the index of the list element (numbering from 0) and q is the value specified by that element.
So, this example would read:
Priority 0 maps to Queue 1
Priority 1 maps to Queue 2
Priority 2 maps to Queue 2
Priority 3 maps to Queue 2
Priority 4 maps to Queue 3
NOTE: The tc priority map applies to a 4-bit field. With the Ethernet Switch Blade, the
priority map refers to the 802.1p tag, which is a 3-bit field. When translating this tc
rule to hardware, only Priorities 0 through 7 are significant; the other eight priorities
are ignored.
The parameters wrr 1 2 4 6 specify that WRR scheduling is being used and assigns a
relative weight to each queue. The weights are treated as numbers of packets to be sent from
each queue. In this example, if the queues have sufficient packets, queue 1 will have twice as
Ethernet Switch Blade User's Guide release 3.2.2j page 122