A Systemd Service to disable CPU C-States at runtime. A hack whilst I tune voltages for stability.

disable-cstate

#! /usr/bin/env bash

SYSFS_FILES_PATTERN="/sys/devices/system/cpu/cpu*/cpuidle/state[$1]/disable"

if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root."
   exit 1
fi

cleanup() {
    echo "Received termination signal. Re-enabling idle states..."
    shopt -s nullglob
    local file_count=0
    for file in $SYSFS_FILES_PATTERN; do
        if [[ -w "$file" ]]; then
            echo "Writing 0 to $file"
            echo 0 > "$file" 2>/dev/null
            file_count=$((file_count + 1))
        fi
    done
    shopt -u nullglob
    if [[ $file_count -eq 0 ]]; then
        echo "Warning: No matching files found to re-enable during cleanup."
    fi
    echo "Cleanup finished. Exiting."
}

trap cleanup SIGINT SIGTERM SIGHUP

echo "Disabling CPU idle states..."
shopt -s nullglob
files_found=0
for file in $SYSFS_FILES_PATTERN; do
    if [[ -w "$file" ]]; then
        echo "Writing 1 to $file"
        echo 1 > "$file" 2>/dev/null
        if [[ $? -ne 0 ]]; then
             echo "Warning: Failed to write to $file"
        else
             files_found=$((files_found + 1))
        fi
    else
        echo "Warning: File $file not found or not writable."
    fi
done
shopt -u nullglob

if [[ $files_found -eq 0 ]]; then
    echo "Error: No matching CPU idle state files found or writable at $SYSFS_FILES_PATTERN"
    echo "Ensure the pattern is correct and you are running as root."
    exit 1
fi

echo "$files_found idle states disabled. Script is running and waiting for termination signal..."
echo "Press Ctrl+C or send SIGTERM (e.g., systemctl stop your-service) to exit gracefully."

sleep inf

disable-cstate.service

[Unit]
After = sysinit.target
Description = Disable CPU C-States
Documentation = https://www.kernel.org/doc/Documentation/power/pm_qos_interface.txt

[Service]
ExecStart = /usr/local/sbin/disable-cstate 2-4
Restart = on-failure
RestartSec = 5s
Type = simple
User = root

[Install]
WantedBy = multi-user.target