Mesa, the open source low level graphics stack, has featured support for Open Compute Language (OpenCL) for some time via a front end called Clover. The problem was that the GPUs that it supported were limited, it didn’t have Image support, and wasn’t really under active development. Around a year ago Karol Herbst filed a merge request adding rusticl to Mesa 22.3 release, and soon after that I enabled it optionally in Fedora.. What is rusticl? It’s a OpenCL API implementation written in rust for Mesa, it will eventually replace clover. One advantage it has is image support from the outset and also works on much wider range of OpenCL capable GPUs, including some ARM GPUs, and the support is actively improving all the time.
In the year since it landed in a stable mesa release rusticl keeps evolving, faster, more HW support, more features, less crashes. I’ve tinkered with it as I’ve had spare time on the weekends and evenings as well as trying to work out details of how you’d use it to run higher level stacks.
As of writing it works with following gallium drivers: iris (Intel), nouveau (Nvidia), radeonsi/r600 (AMD ATI), and panfrost (Arm MALI). There’s other drivers that are various stages of development but are not yet upstream.
So let’s get the basics up and running on Fedora if you have supported hardware. First install the core software stack:
$ sudo dnf install -y mesa-libOpenCL mesa-dri-drivers spirv-llvm-translator spirv-tools-libs clinfo clpeak
Next we run clinfo and clpeak with required parameters, from the driver names above (in this case an Intel laptop), to enable rusticl. The two commands output a lot of information so I’m not going to post them here but the output shows OpenCL running and some details about what’s supported:
$ RUSTICL_ENABLE=iris clinfo --list WARNING: OpenCL support via iris+clover is incomplete. For a complete and conformant OpenCL implementation, use https://github.com/intel/compute-runtime instead Platform #0: rusticl `-- Device #0: Mesa Intel(R) Xe Graphics (TGL GT2) Platform #1: Portable Computing Language `-- Device #0: cpu-11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz Platform #2: Clover $ RUSTICL_ENABLE=iris clinfo output a lot of details $ RUSTICL_ENABLE=iris clpeak output a lot of details
This gets up the basic pieces up and running for OpenCL, there’s of course more to do and not all use cases are complete. Eventually we won’t need to have the environment variables to enable rusticl. The details of drivers and other features enabled by environment variables are documented here. I plan to do some more posts as follow ups to build on this basis.