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AVB: High CPU utilization due to gPTP process with a large number of active AVB ports.

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TitleAVB: High CPU utilization due to gPTP process with a large number of active AVB ports.
Symptoms
  • gPTP process consumes nearly 100% of CPU
  • AVB ports are reporting as AVB incapable
  • AVB Ports are seen in the gPTP disabled role
  • AVB streams performing incorrectly or failing

 
Environment
  • Summit X430, X440, or X460
  • EXOS 15.3.X and newer
  • AVB enabled and active on greater than 20 ports on a single switch
  • Large number of AVB streams (approximately greater than 75)
Cause
The gPTP process is CPU intensive.  As the number of ports actively participating in gPTP increases, the amount of CPU cycles required increases.  This combined with potentially high CPU utilization from other processes causes instability in the gPTP protocol and can cause gPTP to function incorrectly.
Resolution
The CPU resources of the X430, X440, and X460 are limited.  If the number of active gPTP ports and AVB streams increases to a point where the gPTP process is consuming the majority of CPU resources (causing AVB failures),  there are three primary options:
  1. Replace the X430, X440, or X460 with a switch model that utilizes a better CPU (X460-G2, X670, or X670-G2.)
  2. Add additional X430, X440, or X460 switches to the network to off-load a portion of the CPU processing to other devices.
  3. Implement configuration modifications that reduce the CPU overhead of some AVB protocols.  The following commands have been tested in production networks and work well in most environments:
configure mrp ports <AVB_PORTS> timers leave 2000
configure msrp rate-limit boundary-change on limit 1 period 2
configure msrp rate-limit reservation on limit 75 period 1

 
Additionally, gPTP configuration modifications can be made to reduce CPU overheard.  These changes are not supported by all endpoint vendors and should be tested prior to implementing in a production environment:
 
configure network-clock gptp ports <AVB_PORTS> sync initial-interval -1 #500 ms interval
configure network-clock gptp ports <AVB_PORTS> sync receipt-timeout 5
configure network-clock gptp ports <AVB_PORTS> peer-delay allowed-lost-responses 5
configure network-clock gptp ports <AVB_PORTS> announce receipt-timeout 5

 
Bi-Amp Systems have confirmed that their AVB endpoint devices do not support the gPTP sync intervals of 250 or 500 ms.  Therefore, the above gPTP changes would not be supported in a Bi-Amp AVB network.

 
Additional notes

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