[YANG] Fix QoS scheduler validation for PIR-only configurations

[yizhenzha]

Why I did it

The current sonic-scheduler.yang model requires CIR whenever PIR is configured. This incorrectly prevents valid PIR-only scheduler profiles, including profiles used for port egress shaping. CIR and PIR should only come in pair in a theoretical two rate policer model, which is not exactly how SONiC QoS scheduler is implemented at runtime.

At runtime, SONiC maps CIR and PIR to separate SAI scheduler attributes:

• CIR maps to the minimum bandwidth rate.
• PIR maps to the maximum bandwidth rate.

These rates can be configured independently. CIR-only provides a minimum bandwidth allocation without a local maximum, while PIR-only provides a maximum shaping rate without a minimum bandwidth guarantee.

Requiring a dummy CIR for a PIR-only profile is not an appropriate workaround. Some SAI implementations do not support a minimum bandwidth rate on a port-bound scheduler and reject such a configuration.

The YANG model should therefore allow CIR and PIR to be absent or configured independently. When both values are present, PIR must still be greater than or equal to CIR.

How I did it

• Removed the YANG constraint requiring CIR to be configured whenever PIR is configured.
• Made the PIR >= CIR validation conditional on CIR being present.
• Preserved the rejection of configurations where both rates are configured and PIR < CIR.

The resulting behavior is:

CIR	PIR	Result
Not configured	Not configured	Valid (same as before)
Configured	Not configured	Valid (same as before)
Not configured	Configured	Valid (changed by this PR, before it is not valid)
Configured	Configured, PIR >= CIR	Valid (same as before)
Configured	Configured, PIR < CIR	Invalid (same as before)

How to verify it

1. Only configure PIR for a scheduler and confirm YANG rejects it on the unpatched model:

$ redis-cli -n 4 hset "SCHEDULER|port_scheduler" type STRICT pir 625000000
(integer) 2
$ redis-cli -n 4 hset "PORT_QOS_MAP|Ethernet0" scheduler port_scheduler
(integer) 1
$ sudo config save -y
$ sudo config reload -y
sonic_yang(3):Data Loading Failed:failed to parse data tree: pir can't be configured without cir.: Data path: /sonic-scheduler:sonic-scheduler/SCHEDULER/SCHEDULER_LIST[name='port_scheduler']/pir
/etc/sonic/config_db.json fails YANG validation! Error: Data Loading Failed
Aborted!

2. Apply the patched YANG model and confirm the same PIR-only config now loads cleanly, and the scheduler and its PIR binding reach the ASIC via orchagent (SCHEDULER table created, applied to the port).

# 1. Reload invoked, patched YANG loads clean
02:14:38.075678  NOTICE wjh-config: 'reload' executing with command: config reload -y
02:14:38.294737  INFO sonic_yang: modd successfully

# 2. Validator translates and evaluatesthe patched schema
02:14:38.420548  INFO sonic_yang: xlateConfigDBtoYang sonic-scheduler:...:SCHEDULER
02:14:38.420616  INFO sonic_yang: xlaEDULER_LIST
02:14:38.422948  INFO sonic_yang: Try to load Data in the tree
(This is the exact step that threw Dabe configured without cir. in thebaseline run 32 seconds earlier — here it passes silently and moves on to the next module.)

# 3. Validation passed — reload proceeds to actually apply config
02:14:38.475908  NOTICE config: 'relo
02:14:57.207980  NOTICE config: 'reload' restarting services...
(~19s gap = normal container stop/songrator/target-restart work, same as any reload.)

# 4. orchagent picks up the reloaded CONFIG_DB and creates the scheduler object
02:15:56.241070  NOTICE swss#orchagenreated [SCHEDULER:port_scheduler]
02:15:56.242328  NOTICE swss#orchagent: :- handleSchedulerTable: Created [SCHEDULER:scheduler.0]
02:15:56.243383  NOTICE swss#orchagenreated [SCHEDULER:scheduler.1]

# 5. orchagent binds the scheduler to t failed in the original bug
02:15:56.289135  NOTICE swss#orchagent: :- handlePortQosMapTable: Applied QoS maps to ports
02:15:57.256423  NOTICE swss#orchagen times: [handlePortQosMapTable: Applied QoS maps to ports]    

Which release branch to backport (provide reason below if selected)

• 202305
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• 202608

Tested branch

• master

Description for the changelog

Allow CIR and PIR to be configured independently in SONiC scheduler profiles.

Link to config_db schema for YANG module changes

https://github.com/sonic-net/sonic-buildimage/blob/master/src/sonic-yang-models/doc/Configuration.md#scheduler

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