How to build Lc0 without OpenCL support (currently automatically picks it up)

[BuddhiLW]

I'm on Ubuntu 23.10, CPU: AMD Ryzen 5 5600X (12) @ 3.700GHz, GPU: AMD ATI Radeon RX 470/480/570/570X/580/580X/590

I'm using nibbler. When I open choose lc0 that I just built, I get:

Plataform version: OpenCL 2.1 AMD-APP (3590.0)
(...)
Error getting device(s): clGetDeviceIDs: -1
Unhandled exception: No Suitable OpenCL device found.

The question becomes, how can I build without the OpenCL support, specified in the build command? I didn't find anything in the documentation related to specifying this.

[mooskagh]

To disable opencl support while building Lc0, pass -Dopencl=false flag to the ./build.sh command (or to meson setup if you call it directly).

If you did build Lc0 with the opencl support, you can still use a different backend when running it.
To do that, pass --backend=<backend> command line argument or Backend <backend> uci parameter (I'm not sure whether it's possible to do in nibbler though), or create a lc0.config file either in the same directory as the lc0 binary, or at ~/.config/lc0/lc0.config, with the following contents:

backend=<backend>

To get the list of the available backends, read the description of the --backend parameter at ./lc0 --help. In your case, the most likely backends that may work are blas and eigen.

blas and eigen backends will only use CPU though. There is a chance that it's possible to run Lc0 on your GPU, but I'm not sure. It may be a good idea to ask in the #help channel of our Discord chat at http://lc0.org/chat