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The behavior of the scheduler for an access port is given below:
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7210 SAS-X and 7210 SAS-R6 OS Quality of Service Guide
Per port scheduler is available and works at line-rate or configured port egress rate
Port scheduler distributes the bandwidth available to all the SAPs using WDRR
scheduling mechanism (that is, all SAPs have equal weights assigned by the system).
Port scheduler uses to two passes – CIR loop and the PIR loop to distribute bandwidth
across SAPs.
→ In the CIR loop, it distributes the available bandwidth to all the SAP in a round-robin
order up to the configured CIR rate (CIR is configured in the aggregate shaper rates
for the SAP).
→ In the PIR loop, it distributes the remaining bandwidth (the bandwidth available after
the CIR loop) to the all the SAPs in a round-robin order (all SAPs are assigned equal
weights by the system) up to the configured PIR rate (PIR is configured in the
aggregate shaper rates for the SAP).
Each SAP has a per SAP scheduler which operates in SP + WDRR mode and an aggregate
per SAP shaper (CIR/PIR). The per SAP scheduler distributes the available bandwidth to
the configured strict and weighted SAP queues, using the configured mode and rates, in 2
passes - CIR loop and PIR loop
The CIR loop distributes the available bandwidth (from the bandwidth allocated to it by
the port scheduler) to all the queues is in the following order:
→ Higher priority strict queue (s) get the bandwidth up to the configured CIR
→ Any remaining bandwidth, if available, is distributed among the lower priority strict
queue (s) up to the configured CIR
→ Any remaining bandwidth, if available, is distributed among the weighted queues (in
the CIR loop, weights are not used and hence the bandwidth is distributed in equal
proportion irrespective of weights configured)
The PIR loop distributes the remaining bandwidth (the bandwidth remaining after CIR
loop) to all the queues in the following order:
→ Higher priority strict queue(s) get the bandwidth, up to the configured PIR
→ Any remaining bandwidth, if available, is distributed among the lower priority strict
queue(s), up to the configured PIR
→ Any remaining bandwidth, if available, is distributed among the weighted queues in
proportion to their configured weights
Each queue can be configured with a queue-mode (strict or weighted) and is associated
with a shaper (which allow for configuration of CIR/PIR). The queue mode determines the
order of scheduling by the SAP scheduler and shaper rate controls the amount of
bandwidth used by the queue.
Schedulers on 7210 SAS-R6
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