Boot log displays "ENERGY_PERF_BIAS: Set to 'normal', was 'performance'"

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Environment

SUSE Linux Enterprise Micro 5
SUSE Linux Enterprise Server 15
SUSE Linux Micro 6

Situation

A warning in the boot log of some SUSE systems shows "ENERGY_PERF_BIAS: Set to 'normal', was 'performance'".

Resolution

The EPB MSR setting can easily be modified via: cpupower set -b X

For example:

# sudo cpupower info
analyzing CPU 2:
perf-bias: 6

# sudo cpupower set -b 0
# sudo cpupower info
analyzing CPU 5:
perf-bias: 0

To make the setting persistent, create the file /etc/systemd/system/cpupower.service with the following content:

[Unit]
Description=CPU powersave
[Service]
Type=oneshot
ExecStart=/usr/bin/cpupower set -b 0
[Install]
WantedBy=multi-user.target

Once the file is created execute:

# sudo systemctl daemon-reload
# systemctl enable --now cpupower.service

Cause

The EPB MSR (ENERGY_PERF_BIAS Machine Specific Register) is a feature of some Intel CPUs. It can be set to a value from 0-15 to tell the CPU (microcode) whether it should prefer performance (0) over powersave (15) power management.

Intel has observed that on many systems after the hardware platform firmware (BIOS/UEFI) finishes initialization, the initial EPB value is 0 ('performance'). While on some systems this is intentional, on others it is due to the system firmware (UEFI/BIOS) not properly initializing the value of the EPB MSR. Intel implemented a fix in the Linux kernel EPB initialization code to set the EPB to value of 6 ('normal') when the Linux kernel boots. After the kernel finishes loading a proper EPB value can then be selected. Unfortunately, this causes a bit of an inconvenience on systems where the system firmware deliberately set EPB to 0 as they will need to set the value back to 0 after Linux loads. However, other systems (where the EPB value is 0 due to not having been properly initialized) have a higher power consumption than intended/desirable which can cause issues for systems operating from battery power (standby/ups power, or laptops).

Additional Information

With regards to https://bugzilla.suse.com/show_bug.cgi?id=1243492

Disclaimer

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