QoS for Gen-3 Adapter Cards and Platforms

Third-generation (Gen-3) Ethernet adapter cards and Ethernet ports on Gen-3 platforms support 4-priority scheduling.

The main differences between Gen-3 hardware and Gen-2 hardware are that on Gen-3 hardware:

SAPs are shaped (that is, no unshaped SAPs)
SAPs and VLANs are shaped by 4-priority schedulers, not 16-priority schedulers
4-priority scheduling is done on a per-SAP basis
backpressure is applied according to relative priority across VLANs and interfaces. That is, scheduling is carried out in priority order, ignoring per-VLAN and per-interface boundaries. Conforming, expedited traffic across all queues is scheduled regardless of the VLAN boundaries. After all the conforming, expedited traffic across all queues has been serviced, the servicing of conforming, best effort traffic begins.

See Scheduling Modes for a summary of scheduler mode support. For information on adapter card generations, refer to the ‟Evolution of Ethernet Adapter Cards, Modules, and Platforms” section in the 7705 SAR Interface Configuration Guide.

The following figure describes the access, network, and hybrid port scheduling behavior for Gen-3 hardware and compares it with the scheduling behavior of Gen-2 hardware.

Table: Scheduling Behavior After for Gen-2 and Gen-3 Hardware
Port Type		Gen-3 Hardware with 4-Priority Mode	Gen-2 Hardware with 4-Priority Mode
Access	Within a SAP	EXP over BE	EXP over BE
	Default configuration	Simple round-robin (RR) scheduling among SAPs	EXP (across all queues, no SAP boundaries) over BE
	H-QoS and MSS aggregate shapers	RR among aggregates based on PIR and CIR (SAP at tier 2, MSS at tier 3)	N/A
Network	Default configuration (8 queues per port)	EXP over BE	EXP over BE
Network	Per-VLAN shaper	EXP over BE	RR among VLAN shapers based on PIR and CIR
Hybrid	Default configuration (8 queues per port)	EXP over BE	EXP (across all SAPs and network queues) over BE
Hybrid	Per-VLAN shaper	RR among VLAN shapers based on PIR and CIR	RR among VLAN shapers based on PIR and CIR

In summary, the following updates to Gen-3 scheduling are implemented:

enabled CIR-based shaping for:
- per-SAP aggregate ingress and egress shapers
- per-customer aggregate ingress and egress shapers
- per-VLAN shaper at network egress when port is in hybrid mode
- access and network aggregate shapers for hybrid ports
disabled backpressure to the FC queues dependent on the relative priority among all VLAN-bound IP Interfaces at:
- access ingress and access egress when port is in access mode
- access ingress and access egress when port is in hybrid mode
- network ingress
- network egress when port is in hybrid mode

Note:

For network egress traffic when the port is in network mode, there is no change to CIR-based shaping for per-VLAN shapers (that is, PIR-based shaping only, CIR-based shaping is not enabled), and backpressure to the FC queues based on the relative priority among all VLAN-bound IP interfaces is still enabled.