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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

123

The sharing watermarks are maximum areas in the shared memory that a given traffic flow can use.

They do not guarantee anything.

When a frame is enqueued into the egress queue system, the frame first consumes from the queue’s

reserved memory area, then from the port’s reserved memory area. When all the frame’s reserved

memory areas are full, it consumes from the shared memory area.

The following provides some simple examples on how to configure the watermarks and how that

influences the resource management.

•

Setting BUF_Q_RSRV_E(egress port = 7, QoS class = 4) to 2 kilobytes guarantees that traffic

destined for port 7 classified to QoS class 4 have room for 2 kilobytes of frame data before frames

can get discarded.

•

Setting BUF_Q_RSRV_I(ingress port = 7, QoS class = 4) to 2 kilobytes guarantees that traffic

received on port 7 classified to QoS class 4 have room for 2 kilobytes of frame data before frames

can get discarded.

•

Setting BUF_P_RSRV_I(ingress port 7) to 10 kilobytes guarantees that traffic received on port 7

have room for 10 kilobytes of data before frames can get discarded.

•

The three reservations above reserve 14 kilobytes of memory in total (2 + 2+ 10 kilobytes) for port 7.

If the same reservations are made for all ports, there are 224 – 11 × 14 = 70 kilobytes left for

sharing. If the sharing watermarks are all set to 70 kilobytes, all traffic groups can consume memory

from the shared memory area without restrictions.

If, instead, setting BUF_PRIO_SHR_E(QoS class = 7) to 70 kilobytes and the other watermarks

BUF_PRIO_SHR_E(QoS class = 0:6) to 20 kilobytes guarantees that traffic classified to QoS

class 7 has 50 kilobytes extra buffer. The buffer is shared between all ports.

•

The BUF_PRIO_SHR_I, BUF_PRIO_SHR_E, REF_PRIO_SHR_I, and REF_PRIO_SHR_E

watermarks can be used for guaranteeing shared resources for each individual QoS class. This is

done by setting QSYS::RES_QOS_MODE so that the watermarks operate on the current

consumption of each QoS class instead of the total use of the shared resources.

3.11.2

Frame Reference Management

Each frame in an egress queue consumes a frame reference, which is a pointer element that points to

the frame’s data in the memory and to the pointer element belonging to the next frame in the queue. The

following illustrations shows how the frame references are used for creating the queue structure.

Figure 37 •

Frame Reference

The shared queue system holds a table of 1911 frame references. The consumption of frame references

is controlled through a set of watermarks. The set of watermarks is the exact same as for the buffer

control. The frame reference watermarks are prefixed REF_. Instead of controlling the amount of

consumed memory, they control the number of frame references. Both reservation and sharing

watermarks are available. For more information, see Table 96, page 122 and Table 97, page 122.

Egress queue, port 7, QoS class 4

Head

Tail

Buffer Memory

Frame References

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