Lightboard Lessons: CPU Hyper-Threads and TMM

In this episode of Lightboard Lessons, Jason details how BIG-IP’s Traffic Management Microkernel (TMM) utilizes Intel’s Hyper-Threading Technology (on applicable platforms) and the impacts depending on the version of TMOS. In versions before 11.5, each hyper-thread has a separate TMM running. In versions 11.5 and later, TMM and control plane tasks are assigned to separate hyper-threads by default, a behavior we call HTSplit. This behavior is controlled by the scheduler.splitplanes.ltm database key.

Note: This video is a result of a great question by community member Aditya. You can read about the background here.


  • K15003: Data plane and control plane tasks use separate logical cores when the BIG-IP system CPU uses Hyper-Threading Technology
  • K23505424: Overview of the HTSplit feature
  • K14358: Overview of Clustered Multiprocessing (11.3.0 and later)
  • K10095: Error Message: Clock advanced by ticks
  • K16469: Certain BIG-IP ASM control plane processes are now pinned to the highest-numbered logical CPU core
Published Sep 06, 2017
Version 1.0

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  • Hi,


    I am back :-)


    Some more questions:


    HTSplit and vCMP - is same rule about even and odd virtual cores apply to vCMP guest? What when we have 1 vCPU vGuest?


    ASM - according to KB ASM is using highest numbered core for part of control plane tasks. Same rule about halting 80% of odd core still applies here - so ASM control plane processes will be throttled to 20% if even core is loaded over 80%?


    Is ASM really limited for those selected control plane task to one and only one core? I've seen configs where highest numbered core was almost constantly loaded 90-100% - I assume mainly by ASM control plane, if only one core can be dedicated to ASM what is an option in such case?




  • Does this cause packet drops, when we see those logs on /var/log/kern? I can see it our box, when we do load tests on certain VIPs and these logs start growing. And the application see timeouts from the VIP


  • you should not see drops from issues related to this message, it's just enforcing the throttle to make sure TMM is handling the load ok.