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Dell EMC SmartFabric OS10 User Guide Release 10.5.1

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Strict priority queuing

OS10 uses queues for egress QoS policy types. Enable strict priority to dequeue all packets from the assigned queue before servicing any other queues. When you assign more than one queue strict priority, the highest number queue receives the highest priority. You can configure strict priority to any number of queues. By default, all queues schedule traffic per WDRR.

Use the priority command to assign the priority to a single unicast queue—this configuration supersedes the bandwidth percent configuration. A queue with priority enabled can starve other queues for the same egress interface.

Create class-map

  1. Create a class-map and configure a name for the class-map in CONFIGURATION mode. 
    class-map type queuing class-map-name
  2. Configure a match criteria in CLASS-MAP mode. 
    match queue queue-id

Define a policy-map

  1. Define a policy-map and create a policy-map name CONFIGURATION mode. 
    policy-map type queuing policy-map-name
  2. Create a queuing class and configure a name for the policy-map in POLICY-MAP mode. 
    class class-map-name
  3. Set the scheduler as strict priority in POLICY-MAP-CLASS-MAP mode. 
    priority

Apply policy-map

  1. Apply the policy-map to the interface in INTERFACE mode or all interfaces in SYSTEM-QOS mode. 
    system qos
    OR 
    interface ethernet node/slot/port[:subport]
  2. Enter the output service-policy in SYSTEM-QOS mode or INTERFACE mode. 
    service-policy {output} type {queuing} policy-map-name

Enable strict priority on class-map and apply the policy-map globally 

OS10(config)# class-map type queuing example-cmap-strictpriority
OS10(config-cmap-queuing)# match queue 7
OS10(config-cmap-queuing)# exit
OS10(config)# policy-map type queuing example-pmap-strictpriority
OS10(config-pmap-queuing)# class example-cmap-strictpriority
OS10(config-pmap-c-que)# priority
OS10(config-pmap-c-que)# exit
OS10(config-pmap-queuing)# exit
OS10(config)# system qos
OS10(config-sys-qos)# service-policy output type queuing example-pmap-strictpriority

Enable strict priority on interface

NOTE: You can apply a policy-map globally in SYSTEM-QOS mode or apply it on the interface. OS10 does not support applying the same policy-map in SYSTEM-QOS mode as well as at the interface level.

However, you can apply a different queuing policy-map in SYSTEM-QOS mode or at the interface level. In this case, the policy-map applied at the interface takes precedence over the policy-map applied globally. 

OS10(config)# interface ethernet 1/1/5
OS10(conf-if-eth1/1/5)# service-policy output type queuing example-pmap-strictpriority

View policy-map 

OS10(conf-if-eth1/1/5)# do show policy-map
 Service-policy(queuing) output: example-pmap-strictpriority
   Class-map (queuing): example-cmap-strictpriority
     priority

Configuration notes

Dell EMC PowerSwitch S4200-ON Series:

If PFC is provisioned, the control packets injected by CPU shares queue-7 while egressing on a front panel interface. If queues other than queue-7 are provisioned as strict priority, it is recommended to provision queue-7 as strict priority too, to reduce latency or loss of control packets.

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