Warning! This program is untested (apart from by myself) and it may damage your hardware! Use at your own risk.

undervolt

undervolt is a program for undervolting Intel CPUs under Linux. It works in a similar manner to the Windows program ThrottleStop (i.e, MSR 0x150). You can apply a fixed voltage offset to one of 5 voltage planes, and override your systems temperature target (CPU will throttle when this temperature is reached).

For more information, read here.

Installing

From PyPi:

$ pip install undervolt

From source:

$ git clone https://github.com/georgewhewell/undervolt.git

Examples

Read current offsets:

$ undervolt --read
temperature target: -0 (100C)
core: 0.0 mV
gpu: -19.53 mV
cache: -30.27 mV
uncore: -29.3 mV
analogio: -70.31 mV

Apply -100mV offset to CPU Core and Cache:

$ undervolt --core -100 --cache -100

Apply -75mV offset to GPU, -100mV to all other planes:

$ undervolt --gpu -75 --core -100 --cache -100 --uncore -100 --analogio -100

Set temperature target to 97C:

$ undervolt --temp 97

Generated the command to run to recreate your Throttlestop settings:

$ undervolt --throttlestop ThrottleStop.ini --tsindex 3
undervolt --core -100.5859375
$ undervolt --throttlestop ThrottleStop.ini
undervolt --core -125.0 --gpu -125.0 --cache -125.0

Usage

$ undervolt -h
usage: undervolt.py [-h] [-v] [-f] [-r] [-t TEMP]
                    [--temp-bat TEMP_BAT] [--throttlestop THROTTLESTOP]
                    [--tsindex TSINDEX] [--core CORE] [--gpu GPU]
                    [--cache CACHE] [--uncore UNCORE] [--analogio ANALOGIO]

optional arguments:
  -h, --help            show this help message and exit
  -v, --verbose         print debug info
  -f, --force           allow setting positive offsets
  -r, --read            read existing values
  -t TEMP, --temp TEMP  set temperature target on AC (and battery power if --temp-bat is not used)
  --temp-bat TEMP_BAT   set temperature target on battery power
  --throttlestop THROTTLESTOP
                        extract values from ThrottleStop
  --tsindex TSINDEX     ThrottleStop profile index
  --core CORE           offset (mV)
  --gpu GPU             offset (mV)
  --cache CACHE         offset (mV)
  --uncore UNCORE       offset (mV)
  --analogio ANALOGIO   offset (mV)

Running automatically on boot

First, create a unit file /etc/systemd/system/undervolt.service with following contents, replacing the arguments with your own offsets:

[Unit]
Description=undervolt

[Service]
Type=oneshot
# If you have installed undervolt globally (via sudo pip install):
ExecStart=undervolt -v --core -150 --cache -150 --gpu -100
# If you want to run from source:
# ExecStart=/path/to/undervolt.py -v --core -150 --cache -150 --gpu -100

Check that your script works:

$ systemctl start undervolt

Then create a timer /etc/systemd/system/undervolt.timer to trigger the task periodically: :

[Unit]
Description=Apply undervolt settings

[Timer]
Unit=undervolt.service
# Wait 2 minutes after boot before first applying
OnBootSec=2min
# Run every 30 seconds
OnUnitActiveSec=30

[Install]
WantedBy=multi-user.target

Now enable and start the timer:

$ systemctl enable undervolt.timer
$ systemctl start undervolt.timer

By including the OnBootSec command, settings will not be immediately applied. If you have set overly-aggressive offsets, you will have a short period to disable the timer before it crashes your system:

$ systemctl stop undervolt.timer

Now you can edit your undervolt.service before re-starting the timer.

Hardware support

Undervolting should work on any CPU later than Haswell.

System	CPU	Working?
Lenovo Yoga 920	i7-8550U	Yes
Lenovo X1 Gen 5	i7-7500U	Yes
Lenovo X1 Yoga Gen 2	i7-7600U	Yes
Lenovo Thinkpad T470p	i7-7700HQ	Yes
Lenovo Thinkpad x250	i7-5600U	Yes
Dell Latitude 5480	i5-6300U	Yes
Dell Latitude 7390	i7-8650U	Yes
Dell Precision M3800	i7-4712HQ	Yes
Dell XPS 13 9343	i5-5200U	Yes
Dell XPS 15 9530	i7-4712HQ	Yes
Dell XPS 15 9550	i7-6700HQ	Yes
Dell XPS 15 9560	i7-7700HQ	Yes
Dell XPS 15 9570	i9-8950HK	Yes
Dell XPS 15 9575	i7-8705G	Yes
HP Spectre X360	i7-8809G	Yes
HP Zbook Studio G5	i7-8750H	Yes
MacBook Air Mid 2013	i5-4250U	Yes
Acer Nitro 5	i5-7300HQ	Yes

Troubleshooting

• Core or Cache offsets have no effect. It is not possible to set different offsets for CPU Core and Cache. The CPU will take the smaller of the two offsets, and apply that to both CPU and Cache. A warning message will be displayed if you attempt to set different offsets.
• OSError: [Errno 1] Operation not permitted First try running with sudo. If the error persists, your system is probably booted in Secure Boot mode. In this case, the Linux kernel will prevent userspace programs (even as root) from writing to the CPU's model-specific registers. Disable UEFI Secure Boot in your system's BIOS and the error should go away.

Credit

This project is a trivial wrapper around the work of others from the following resources:

• https://github.com/mihic/linux-intel-undervolt
• http://forum.notebookreview.com/threads/undervolting-e-g-skylake-in-linux.807953
• https://forums.anandtech.com/threads/what-controls-turbo-core-in-xeons.2496647

Many thanks to all who contributed.