Support for open drivers

[jansol]

The open source kernel modules export several metrics and other GPU monitors (e.g. nvtop, radeontop, KDE System Monitor) can display them.

[ProjectPhysX]

Hi Jan,

I've looked into nvtop and intel_gpu_top codebases. They use magic ioctl() syscalls, which look a bit scary.
Do you have some good learning resources for that?

Kind regards,
Moritz

[jansol]

Sure thing!

A popular option is to just punt the whole thing off to the libsensors / lm-sensors library. That basically simply reads the kernel's unified HWMON interface sysfs files, so if you prefer to keep dependencies to a minimum it's not too hard to roll your own implementation either. The libdrm library has a bunch of similar functions that work similarly through the DRM subsystem's stats interface

In general the Linux GPU Driver Developer Guide is a good starting point, although making sense of the way it's structured might take a while.

AMDGPU is easily the most beginner-friendly since you can simply cat/read() all the info about power & thermals and more, e.g. vram stats from /sys/class/hwmon/hwmon*/* and they are well documented in the guide. Some of these are also replicated to the DRM subsystem, so they are also found in /sys/class/drm/card[0-127]/ (the subdirectories without a connector in the name).

For Intel you have a whole performance tracing setup and from a quick look at igt-gpu-tools/gputop it seems to use that through the sysfs. Xe and i915 have separate chapters in the guide but I didn't see any Xe-specific monitoring interface so chances are that a lot of it is shared with i915.

The GPU Driver Developer Guide also points to the DRM client stats uAPI for Intel and mobile GPUs. The DRM subsystem seems to really like its IOCTLs, so for that you'll want to read the magic IOCTL explainer (or let libdrm handle them like radeontop apparently does).