Warning - could not determine the number of cstates

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9
  • AMD EPYC CPU
  • Intel CPU

Issue

  • Cpuscaling test gives the following warning in the Hardware Certification
Warning - could not determine the number of cstates using command:
#ls -1 /sys/devices/system/cpu/cpu0/cpuidle | wc -l
Enabling all cstates

stderr:
#ls: cannot access '/sys/devices/system/cpu/cpu0/cpuidle': No such file or directory
  • Cannot see anything in /sys/devices/system/cpu/cpuidle/current_driver

Resolution

AMD:

  • Enable the C-state in BIOS.

Intel:

  • Enable the MWAIT in BIOS and follow the below step to make sure the intel_idle driver is loaded.
# cat /sys/devices/system/cpu/cpuidle/current_driver
intel_idle

Root Cause

  • The C-state/MWAIT option is disabled in BIOS causing the C-state warning.

Diagnostic Steps

  • Check the current "scaling" driver.
 # cat /sys/devices/system/cpu/cpufreq/policy0/scaling_driver
acpi-cpufreq
  • As for idle driver, none is loaded.
# cat /sys/devices/system/cpu/cpuidle/current_driver
none

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