Brocade Network OS Command Reference v4.1.0 - Manual (Page 632)

594 Network OS Command Reference
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qos rcv-queue cos-threshold
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qos rcv-queue cos-threshold
Configures the port tail drop thresholds.
Synopsis qos rcv-queue cos-threshold TDT0 {TDT1 | TDT2 | TDT3 | TDT4 | TDT5 | TDT6 | TDT7}
no qos rcv-queue cos-threshold
Operands TDT0 Defines the proportion for the first port tail drop threshold. Valid values
range from 0 through 100.
TDT1 Defines the proportion for the second port tail drop threshold. Valid values
range from 0 through 100.
TDT2 Defines the proportion for the third port tail drop threshold. Valid values
range from 0 through 100.
TDT3 Defines the proportion for the fourth port tail drop threshold. Valid values
range from 0 through 100.
TDT4 Defines the proportion for the fifth port tail drop threshold. Valid values
range from 0 through 100.
TDT5 Defines the proportion for the sixth port tail drop threshold. Valid values
range from 0 through 100.
TDT6 Defines the proportion for the seventh port tail drop threshold. Valid values
range from 0 through 100.
TDT7 Defines the proportion for the eighth port tail drop threshold. Valid values
range from 0 through 100.
Defaults None
Command Modes Interface subconfiguration mode (gi, te).
Description Use this command to configure the port tail drop thresholds.
Every port has associated with it a total of nine CoS thresholds, one for the port tail drop threshold
and the other eight are thresholds for per priority. To give a fair allocation of buffers for the traffic
from all priorities, the port buffers are allocated among different priorities. That is achieved
through per priority tail drop thresholds. The port tail drop threshold represents the amount of
buffers given to the port and per priority tail drop thresholds (CoS tail drop thresholds from now on)
represents the buffers allocated to each CoS.
Whenever the buffers allocated to a priority are fully exhausted, all the traffic coming in on that
priority is dropped. In the absence of per priority tail drop thresholds (and only port tail drop
threshold), the buffers would be consumed on a first come first serve basis and results in an
unfair share of buffers between all the priorities.
If you know which priority traffic is most seen, then giving good number of buffers for those
priorities results in less number of packet drops for those priorities. Therefore, instead of using the
standard priority values, you can assign any priority from 0% to 100% to any threshold; however,
the sum value of all eight priorities must not exceed 100%. For example, using the priorities
5 5 5 5 50 20 2 8 sums up to 100%.