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small packet probability review feedback
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  • content/cumulus-linux-517/Layer-1-and-Switch-Ports/Quality-of-Service

content/cumulus-linux-517/Layer-1-and-Switch-Ports/Quality-of-Service/_index.md

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@@ -718,10 +718,10 @@ small-packet-probability 60
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Lossless headroom based on small packet probability is a Beta feature.
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{{%/notice%}}
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Cumulus Linux calculates the headroom size for lossless priority groups based on the assumption that all packets are small (64 bytes). On Spectrum-5 and earlier, the switch assumes a 100 percent probability of such packets arriving at line rate.
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<!--On Spectrum-6, the switch assumes a 50 percent probability of such packets arriving at line rate. As a result, the configured headroom is often larger than necessary, as traffic typically consists of a mix of packet sizes.-->
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Cumulus Linux calculates the headroom size for lossless priority groups based on the assumption that all packets are small (64 bytes). On Spectrum-5 and earlier, the switch assumes a 100 percent probability of such packets arriving at line rate. As a result, the configured headroom is often larger than necessary, as traffic typically consists of a mix of packet sizes.
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<!--On Spectrum-6, the switch assumes a 50 percent probability of such packets arriving at line rate.-->
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To enable more accurate headroom calculations, providing for better buffer allocation and improved shared buffer utilization, you can configure the probability of small packets on ports applied with {{<link url="#priority-flow-control-(pfc)" text="priority flow control">}}. Based on the configured small packet probability, `switchd` calculates the headroom reservation required for the lossless priority group.
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To enable more accurate headroom calculations, providing for better buffer allocation and improved shared buffer utilization, you can configure the probability of small packets on ports applied with a {{<link url="#priority-flow-control-(pfc)" text="priority flow control profile">}}. Based on the configured small packet probability, `switchd` calculates the headroom reservation required for the lossless priority group.
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{{< tabs "TabID679 ">}}
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{{< tab "NVUE Commands ">}}
@@ -766,25 +766,26 @@ To show the PFC small packet probability setting for a profile, run the `nv show
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```
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cumulus@switch:~$ nv show qos pfc default-global
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operational applied pending
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----------------- ----------- ------- -------
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cable-length 100
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small-packet-probability 60
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tx enable
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rx enable
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[switch-priority] 3
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operational applied
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------------------------ ----------- -------
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cable-length 100 100
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small-packet-probability 40 40
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tx enable enable
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rx enable enable
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[switch-priority] 3 3
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```
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<!--
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To show the link pause small packet probability setting for a profile, run the `nv show qos link-pause <profile-id>` command. To show the link pause small packet probability setting for an interface, run the `nv show interface <interface-id> qos link-pause` command.
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```
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cumulus@switch:~$ nv show qos link-pause default-global
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operational applied pending
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------------------------ ----------- ------- -------
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cable-length 100
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small-packet-probability 60
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tx enable
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rx enable
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operational applied
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------------------------ ----------- -------
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cable-length 100 100
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small-packet-probability 40 40
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tx enable enable
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rx enable enable
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[switch-priority] 3 3
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```
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-->
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### PFC Watchdog

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