Rapl Energy

Small library for getting the CPU energy consumption from RAPL and friends.

This project is very much still a work in progress, and is mainly intended for internal use. However, I share it here should it be useful to anyone.

RAPL permissions

Reading RAPL requires elevated permissions.

I suggest adding a new rapl group.

sudo addgroup rapl
sudo usermod -aG rapl $(whoami)

And then adding entries to /etc/sysfs.conf for your RAPL domains and subdomains. Check your folder hierarchy in /sys/class/powercap/ to determine which domains you have available to your CPU.

Then for each domain, add the following lines to /etc/sysfs.conf. (Requires sysfsutils to be installed.)

For example, for package 0:

mode class/powercap/intel-rapl:0/energy_uj = 0440
owner class/powercap/intel-rapl:0/energy_uj = root:rapl

And for its first subdomain:

mode class/powercap/intel-rapl:0:0/energy_uj = 0440
owner class/powercap/intel-rapl:0:0/energy_uj = root:rapl

Finally, restart the sysfsutils service.

sudo systemctl restart sysfsutils

MSR permissions

Reading model-specific registers (MSR) requires elevated permissions.

sudo apt install msr-tools

You might need to run modprobe as well.

modprobe msr

One can then print the accumulated energy value as follows. (Where -a prints all CPUs, and -u prints the value as an unsigned decimal.) On my AMD system the address is 0xC001029A, which I found in https://github.com/amd/amd_energy. Check the documentation of your CPU to find your address.

sudo rdmsr 0xC001029A -au

Any executable making use of these MSR measurements must be run with sudo.

sudo ./target/debug/examples/msr

MSR group

Ideally I would like to create a group for MSR, to avoid needing to run with sudo every time. However, the approach below sadly does not resolve the problem. Please let me know if you know of a way to do this.

sudo groupadd msr
sudo chgrp msr /dev/cpu/*/msr
sudo chmod g+rw /dev/cpu/*/msr
sudo usermod -aG msr $(whoami)
newgrp msr