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Cornelis Technical Documentation

6.3. Linux Settings

6.3.1. CPU Frequency Scaling

Methods for power saving on CPUs can impact performance inversely. By reducing the CPU clock frequency based on sustained demand and thermal conditions, CPUs reduce power consumption. However, this can result in reduced performance or increased variability in performance metrics due to unpredictable thermal conditions.

  • The default scaling driver for Intel processors in RHEL 9.x is the Intel P-State (intel_pstate) driver.

  • For AMD processors, the default is ACPI CPUfreq (acpi_cpufreq), with the option to use the newer AMD P- State (amd_pstate) driver if CPPC is supported.

Setting your frequency scaling driver for maximum performance is recommended during initial system bring-up to verify peak cluster capabilities.

Note

The following instructions apply only to Intel processors. For AMD, use the default acpi_cpufreq or amd_pstate, if available.

6.3.1.1. Intel P-State Driver

No setup is required as intel_pstate is the default in RHEL 9. For optimal performance:

  • Ensure Turbo Boost is enabled in BIOS.

  • Enable the performance governor.

6.3.1.1.1. Key Runtime Tuning (no reboot required)

Set minimum performance percentage to 100%

echo 100 > /sys/devices/system/cpu/intel_pstate/min_perf_pct

Set performance governor

cpupower frequency-set -g performance

To check CPU frequency settings:

cpupower frequency-info

For better frequency monitoring, use:

turbostat
6.3.1.1.2. Re-Enabling intel_pstate (if previously disabled)

  1. Edit /etc/default/grub and remove intel_pstate=disable.

  2. Update GRUB:

    On RHEL and SLES:

    grub2-mkconfig --update-bls-cmdline -o /etc/grub2.cfg

    On Ubuntu:

    update-grub

  3. Reboot.

For more information, refer to Intel P-State driver - Kernel.org.

6.3.1.2. ACPI CPUfreq Driver

Only needed if intel_pstate does not meet your needs.

6.3.1.2.1. To Enable acpi_cpufreq on Intel CPUs

  1. Edit /etc/default/grub, add:

    intel_pstate=disable

  2. Update GRUB:

    bash grub2-mkconfig --update-bls-cmdline -o /etc/grub2.cfg

  3. Reboot.

6.3.1.2.2. CPU Frequency Governor

Ensure that the performance CPU frequency governor is enabled.

sudo cpupower -c all frequency-set -g performance
6.3.1.2.3. Turbo Mode

To enable Turbo mode, use slightly higher frequency (for example, 2.301 GHz for a CPU with a base frequency of 2.3GHz):

sudo cpupower -c all frequency-set --min 2.301GHz --max 2.301GHz -g performance

Note

This increases heat and power draw.