Overview
Page 392 7210 SAS D, E, K OS Quality of Service Guide
Overview
The 7210 SAS-K devices supports strict Priority and WFQ mode of scheduling or a mix of both.
Schedulers are used at SAP ingress, SAP egress, Access Uplink Port ingress and Access-uplink
port egress.
The scheduler uses 2 loops - the CIR loop and PIR loop, each with 4 priorities. The configured
priority of the queue determines the service order of the queue in the CIR loop and the PIR loop.
The scheduler first goes through the CIR loop, where it services all the queues which are operating
at less than CIR rate according to the priority (that is, higher priority queues get services earlier
than lower priority queues). It thereafter goes through the PIR loop, where it services all the
queues which are operating above the CIR rate (but less than PIR rate) according to the priority
(that is, higher priority queues get services earlier than lower priority queues). If there are multiple
queues configured with the same priority, in the CIR loop the queues are scheduled using WFQ,
with the configured weight of the queue used to determine the proportion of the available
bandwidth that is given to the queue. In the PIR loop, the queues are scheduled using WFQ, with
the configured weight of the queue used to determine the proportion of the available bandwidth
that is given to the queue (using WFQ). In the PIR loop, the queues are scheduler until the PIR rate
is met or until no more bandwidth is available. If the PIR rate is met, then the queues are not
scheduled anymore.
The diagram below shows the scheduler implemented in 7210 SAS-K
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