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Improve Measurement Accuracy with RAPL

RAPL (Running Average Power Limit) is a hardware feature on modern Intel and AMD processors that provides direct energy measurements through CPU counters. Enabling RAPL access gives CodeCarbon significantly more accurate CPU power measurements compared to software-based estimation.

How RAPL Improves Accuracy

Without RAPL, CodeCarbon estimates CPU power based on hardware specifications and CPU load. With RAPL enabled, CodeCarbon reads actual energy consumption directly from the processor's energy counters, providing:

  • ✅ Direct hardware measurements — Read CPU energy directly from RAPL counters
  • ✅ Higher precision — Microjoule-level accuracy instead of estimates
  • ✅ Multi-domain support — Measure package, core, uncore, DRAM, and GPU separately
  • ✅ Real-time data — No delay or aggregation artifacts

Prerequisites

  • Linux system with RAPL-capable CPU (Intel Skylake or newer, AMD Ryzen, EPYC, etc.)
  • Linux kernel 5.8+ (for AMD CPU support)
  • sudo access to configure permissions
  • CodeCarbon installed

Check RAPL Availability

First, verify that your CPU supports RAPL:

ls /sys/class/powercap/intel-rapl*

If the command returns directories (e.g., intel-rapl:0, intel-rapl:1), your system has RAPL support.

Setup Steps

Step 1: Understand the Security Issue

Due to CVE-2020-8694, Linux distributions restrict RAPL file permissions to root-only for security. This prevents unprivileged users from reading fine-grained power data.

Step 2: Temporary Access (Testing)

To quickly test RAPL without permanent changes:

sudo chmod -R a+r /sys/class/powercap/*

This grants read access to all users. However, permissions are lost at next reboot, so this is only for testing.

For permanent access that survives reboots, use sysfsutils:

Step 3a: Install sysfsutils

sudo apt install sysfsutils

Step 3b: Configure RAPL Permissions

Edit the sysfsutils configuration:

sudo nano /etc/sysfs.conf

Add this line at the end:

mode class/powercap/intel-rapl:0/energy_uj = 0444

Save and exit (Ctrl+X, then Y, then Enter).

Step 3c: Reboot to Apply Changes

sudo reboot

Step 4: (Optional) More Restrictive Permissions

For better security, you can create a dedicated group instead of allowing all users:

# Create a codecarbon group
sudo groupadd codecarbon

# Add your user to the group
sudo usermod -a -G codecarbon $USER

# Update sysfs.conf with group permissions
sudo nano /etc/sysfs.conf

Update the line to:

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

Log out and back in for group membership to take effect:

logout
# Then log back in

Step 5: Verify RAPL Access

Test that CodeCarbon can now read RAPL data:

python -c "from codecarbon import EmissionsTracker; t = EmissionsTracker(); t.start(); import time; time.sleep(5); print(t.stop())"

Check the output for CPU Tracking Method: RAPL to confirm RAPL is active.

Docker and Containerized Environments

If running CodeCarbon in Docker, mount the RAPL sysfs:

docker run --device /sys/class/powercap:/sys/class/powercap:ro <image>

Or in docker-compose.yml:

volumes:
  - /sys/class/powercap:/sys/class/powercap:ro

Learn More

To understand RAPL in detail, including domain hierarchy, double-counting issues, and CodeCarbon's domain selection strategy, see:

Next Steps

  • Linux Service — Configure RAPL permissions when running CodeCarbon as a background service
  • SLURM — Enable RAPL on HPC clusters
  • Configure CodeCarbon — Customize which RAPL domains to measure