When port-scheduler mode is enabled, traffic sent out of SAPs configured on access ports and hybrid ports, share a set of eight egress queues that are mapped to the eight forwarding classes. A per-port scheduler (similar to the one available for network port) distributes the available port bandwidth to all the queues configured on the port in two passes using similar behavior to the per-SAP scheduler.
The per-SAP scheduler is not present in the scheduler hierarchy when port-scheduler mode is enabled.
The following figure shows the port-based scheduling and queuing enabled on access ports on the 7210 SAS-R6 and 7210 SAS-R12.
Port-based queuing and scheduling on access ports has the following behavior:
If enabled, all SAPs on the node use port-based queuing. This means that the user has an option to use either SAP-based queues for all SAPs configured on the node, or port-based queues for all SAPs configured on the node. A mix and match of some SAPs using port-based queues and some SAPs using SAP-based queues is not supported
All SAPs on an access port share the eight egress queues on the port. On hybrid ports, SAPs use network port queues, which means that, on hybrid ports, all the SAPs configured on the port and the network port IP interfaces share the eight egress queues on the port.
This functionality supports two-level hierarchical shaping, with per-queue shaper and per-port aggregate shaper (ERL).
Each FC or queue of the port can be shaped to configured rates (CIR/PIR). This is used to control the amount of bandwidth allocated to the FC or queue.
FC-to-queue mapping is system-defined and not user configurable.
The queue number determines the priority of the queue. Priority of the queue is used only when the queues are configured as strict. Queue 8 is the highest priority and queue 1 is the lowest priority.
A queue can be defined to operate in strict mode or weighted mode. The queue mode determines the order of scheduling by the port scheduler.
The scheduling behavior is similar to the scheduling behavior that is supported on SAPs with the following modifications:
Each access port has a per-port scheduler that operates in SP + WDRR mode and an aggregate per-port shaper (ERL). The per-port scheduler distributes the available bandwidth to the configured strict and weighted queues, using the configured mode and rates, in two passes: CIR loop and PIR loop.
The CIR loop distributes the available bandwidth to all the queues in the following order:
Higher priority strict queues receive bandwidth up to the configured CIR.
Any remaining bandwidth, if available, is distributed among the lower priority strict queues 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 therefore the bandwidth is distributed in equal proportion irrespective of weights configured)
The PIR loop distributes the bandwidth remaining after CIR loop to all the queues in the following order:
Higher priority strict queues receive the bandwidth, up to the configured PIR.
Any remaining bandwidth, if available, is distributed among the lower priority strict queues, up to the configured PIR.
Any remaining bandwidth, if available, is distributed among the weighted queues in proportion to their configured weights.