Power Management¶

APU power and thermal control for balancing performance, power consumption, and noise.

CPU Power Governors¶

cpupower Tool¶

Install CPU frequency utilities:

sudo apt install -y linux-tools-common linux-tools-$(uname -r)

View current governor:

cpupower frequency-info

Available Governors¶

Governor	Behavior	Use Case
performance	Max frequency always	LLM inference, benchmarks
powersave	Min frequency always	Idle, overnight
schedutil	Dynamic, kernel-driven	Default, balanced
ondemand	Dynamic, userspace	Legacy systems

Set governor temporarily:

sudo cpupower frequency-set -g performance

Persistent Governor¶

Create a systemd service for boot-time setting:

# /etc/systemd/system/cpupower.service
[Unit]
Description=Set CPU governor
After=multi-user.target

[Service]
Type=oneshot
ExecStart=/usr/bin/cpupower frequency-set -g schedutil
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Enable:

sudo systemctl enable cpupower.service

AMD P-State Driver¶

Modern AMD processors use the amd-pstate driver for efficient power management.

Verify Driver¶

# Check active driver
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver

Expected output: amd-pstate or amd-pstate-epp

P-State Modes¶

Mode	Description
amd-pstate	Basic frequency scaling
amd-pstate-epp	Enhanced with Energy Performance Preference

Enable EPP mode via kernel parameter:

# /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amd_pstate=active"

Update GRUB:

sudo update-grub

Energy Performance Preference (EPP)¶

EPP allows fine-tuning the power/performance balance:

# View current EPP
cat /sys/devices/system/cpu/cpu0/cpufreq/energy_performance_preference

# Available options
cat /sys/devices/system/cpu/cpu0/cpufreq/energy_performance_available_preferences

Options:

EPP Value	Behavior
performance	Maximum performance
balance_performance	Slight performance bias
balance_power	Slight power saving bias
power	Maximum power saving

Set EPP for all cores:

for cpu in /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference; do
    echo "balance_performance" | sudo tee "$cpu"
done

Platform Power Profiles¶

power-profiles-daemon¶

Ubuntu includes power-profiles-daemon for system-wide power management:

# Check status
powerprofilesctl

Available Profiles¶

Profile	Description
performance	Maximum performance, higher power
balanced	Default, adaptive behavior
power-saver	Reduced power, lower performance

Set profile:

# Switch to performance
powerprofilesctl set performance

# Switch to balanced
powerprofilesctl set balanced

# Switch to power-saver
powerprofilesctl set power-saver

Profile Effects¶

The power profile affects:

CPU frequency scaling
GPU power states
Platform power limits
Turbo boost behavior

Thermal Management¶

Temperature Monitoring¶

Monitor temperatures continuously:

watch -n 2 sensors

Key temperature points:

Component	Target	Throttle
CPU (Tctl)	< 80C	~95C
GPU	< 85C	~100C
NVMe	< 60C	~80C

Thermal Throttling¶

Check if thermal throttling is occurring:

# CPU throttle events
dmesg | grep -i throttl

# Current vs max frequency
cpupower frequency-info | grep -E "(current|hardware limits)"

Thermal Relationship¶

Higher TDP (power limit) means:

More performance
Higher temperatures
More fan noise

Reducing power limits via BIOS or kernel parameters can lower temperatures at the cost of performance.

When to Reduce Power¶

Consider power reduction when:

Thermal throttling occurs frequently
Fan noise is unacceptable
Ambient temperature is high
Running sustained workloads

Fan Control¶

BIOS vs OS Control¶

Most systems manage fans via BIOS/firmware. Check current fan status:

sensors | grep -i fan

fancontrol (if applicable)¶

Some systems support OS-level fan control:

sudo apt install -y fancontrol

# Configure (if supported)
sudo pwmconfig

Note

Many modern systems, especially laptops and SFF PCs, don't expose fan control to the OS. Fan curves are managed in BIOS.

Noise Considerations¶

Fan Behavior	Cause	Solution
Constant high speed	High sustained load	Reduce power profile
Ramps up/down frequently	Bursty workloads	Adjust fan curve in BIOS
Always loud	Aggressive fan curve	Modify BIOS settings

Workload-Based Profiles¶

High-Performance Profile¶

For LLM inference and compute-intensive tasks:

#!/bin/bash
# /usr/local/bin/profile-performance.sh

powerprofilesctl set performance

for cpu in /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference; do
    echo "performance" | sudo tee "$cpu" > /dev/null
done

echo "Performance profile activated"

Balanced Profile¶

For mixed workloads (default):

#!/bin/bash
# /usr/local/bin/profile-balanced.sh

powerprofilesctl set balanced

for cpu in /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference; do
    echo "balance_performance" | sudo tee "$cpu" > /dev/null
done

echo "Balanced profile activated"

Quiet Profile¶

For idle or overnight operation:

#!/bin/bash
# /usr/local/bin/profile-quiet.sh

powerprofilesctl set power-saver

for cpu in /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference; do
    echo "power" | sudo tee "$cpu" > /dev/null
done

echo "Quiet profile activated"

Install Profile Scripts¶

sudo chmod +x /usr/local/bin/profile-*.sh

Switch profiles as needed:

# Before LLM inference
sudo profile-performance.sh

# Back to normal
sudo profile-balanced.sh

# Overnight
sudo profile-quiet.sh

Automatic Profile Switching¶

Create a systemd service for overnight quiet mode:

# /etc/systemd/system/quiet-night.timer
[Unit]
Description=Enable quiet mode at night

[Timer]
OnCalendar=*-*-* 23:00:00
Persistent=true

[Install]
WantedBy=timers.target

# /etc/systemd/system/quiet-night.service
[Unit]
Description=Enable quiet profile

[Service]
Type=oneshot
ExecStart=/usr/local/bin/profile-quiet.sh

And a corresponding morning timer to restore balanced mode.

Quick Reference¶

Task	Command
View current governor	`cpupower frequency-info`
Set governor	`sudo cpupower frequency-set -g <gov>`
View power profile	`powerprofilesctl`
Set power profile	`powerprofilesctl set <profile>`
Check EPP	`cat /sys/devices/system/cpu/cpu0/cpufreq/energy_performance_preference`
Monitor temps	`watch -n 2 sensors`
Check throttling	`dmesg \\| grep -i throttl`