pcc-cpufreq driver is not recommended for > 4 CPUs machines

Solution In Progress - Updated -

Issue

Due to the design limitations of pcc-cpufreq driver and Processor Clocking Control feature, this driver can cause high %sys time depending on workload.
Usually the common issue is when workload is quite unstable and vary and often switches between being CPU-bound and I/O-bound behaviour. Also, if a lot of tasks/threads appear and migrates to different CPUs in and out the issue can get worse.
In such case kernel can occupy the CPUs for a long time causing high %sys load.

Environment

  • RHEL 7
  • RHEL 8
  • "ondemand", "schedutil" or "conservative" cpufreq governor is used
  • usually pcc-cpufreq driver is used on HP machines but can be present on another machines

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