Enviroment

• RHEL9.1
• aarch64

Issue

• The CPPC cpufreq driver is failing to load in RHEL 9.1 on ARM servers. This is causing CPU scaling to fail on affected Arm platforms

Diagnostic Steps

# cpupower frequency-info
analyzing CPU 0:
  no or unknown cpufreq driver is active on this CPU
  CPUs which run at the same hardware frequency: Not Available
  CPUs which need to have their frequency coordinated by software: Not Available
  maximum transition latency:  Cannot determine or is not supported.
Not Available
  available cpufreq governors: Not Available
  Unable to determine current policy
  current CPU frequency: Unable to call hardware
  current CPU frequency:  Unable to call to kernel

Solution

This is due to a regression bug on RHEL 9.1, and can not be fixed on this minor version. But it will be fixed on RHEL9.2 and later version. If you are using RHEL9.0/RHEL9.1 on a Red Hat certified ARM platform, and you would like to upgrade the system to use cpuscaling, we suggest you to upgrade the system to RHEL9.2 to avoid the issue. This bug does not cause any system instability but it does prevent affected CPUs from scaling down from their highest advertised frequency. Affected systems will be unable to scale down to lower frequencies during periods of downtime and this can cause an increase in power consumption.