Configuring PFC Deadlock Detection

CloudEngine 16800, 8800, and 6800 Series Switches AI Fabric Deployment Best Practices

This document describes the best practices for deploying the AI Fabric intelligent and lossless data center network solution (referred to as AI Fabric solution), helping network engineers understand how to use the functions provided by the AI Fabric solution to implement zero packet loss, low latency, and high throughput on data center networks.

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Configuring PFC Deadlock Detection

Commands are provided for each PFC deadlock monitoring operation. Table 2-6 lists the steps and recommended configurations for PFC deadlock detection on leaf switches.

Table 2-6 Recommended PFC deadlock detection configurations

Operation	Command	Recommended Configurations
Deadlock detection and determination	Run the priority priority deadlock-detect time time command to set the interval for hardware-based deadlock detection.	The time unit of the deadlock detection interval is determined by the precision of the deadlock detection interval. The actual value that takes effect is the product of time multiplied by interval-value. The value of interval-value can be 10 or 100, in milliseconds, and is 100 by default. If time time is set to 1, that is, the hardware-based deadlock detection interval is 110 ms or 1100 ms, packet loss may occur because the switch incorrectly detects a deadlock.
Deadlock detection and determination	Run dcb pfc deadlock-detect interval interval-value to set the accuracy of the hardware-based PFC deadlock detection interval and recovery time.
Deadlock recovery	Run the priority priority deadlock-recovery time time command to set the hardware-based deadlock detection recovery time.	Similar to the deadlock detection interval, the time unit of the deadlock detection recovery time is determined by the precision of the deadlock detection recovery time. The actual value that takes effect is the product of time multiplied by interval-value. If the deadlock precision is changed to 10 ms, the system automatically adjusts the deadlock recovery time to an integer multiple of 100 ms. For example, if the deadlock recovery time is set to 11 and the deadlock detection accuracy is 10 ms, the deadlock recovery time that actually takes effect is 200 ms. If the packet processing behavior during deadlock recovery is set to discard, a few packets may be forwarded. You can configure a long detection period and a long recovery period to reduce the number of forwarded packets.
Deadlock recovery	Run the dcb pfc deadlock recovery-behavior { discard \| forwarding } slot slot-id command to configure the device to discard or forward packets during hardware-based deadlock recovery. By default, a device forwards packets during hardware-based deadlock recovery.
Deadlock control	Run the priority priority turn-off threshold threshold command to configure the device to automatically disable PFC upon a specified number of times of deadlocks within a specified period of time.	If PFC is required after it is automatically disabled, run the undo dcb pfc enable command in the interface view to disable PFC first. Then run the dcb pfc enable command to enable PFC, and re-configure PFC. If the number of deadlocks reaches the threshold within 1 minute, the system automatically disables PFC and reports the QOS_1.3.6.1.4.1.2011.5.25.32.4.1.11.73 hwXQoSPfcTurnOffAlarm alarm.
Description	After any of the preceding commands is configured, the hardware-based deadlock detection function is enabled. If you need to modify the PFC deadlock detection configuration, run the shutdown command to disable all the interfaces where the PFC profile is applied to prevent configuration failures caused by deadlock recovery on the device.

Recommended settings:

Table 2-7 lists the recommended settings for common models.

Table 2-7 Recommended PFC hardware-based deadlock detection parameter settings for common models

Device Model	Deadlock Detection Interval	Deadlock Recovery Time
CE6865-48S8CQ-EI, CE8850-64CQ-EI	100 ms	100 ms
CloudEngine 16800	1500 ms	1500 ms

After the configuration is complete, run the display dcb pfc interface command to check the number of PFC deadlocks and recovery times.

<HUAWEI> display dcb pfc interface 100ge 1/0/1 
-----------------------------------------------------------------------------------------
Interface         Queue         Received(Frames)        ReceivedRate(pps)     DeadlockNum
                             Transmitted(Frames)     TransmittedRate(pps)     RecoveryNum
-----------------------------------------------------------------------------------------
100GE1/0/1            3                   148990                       99               0
                                               0                        0               0
-----------------------------------------------------------------------------------------

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Updated: 2021-12-16

Document ID: EDOC1100155250

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