Ryzen + RX 580 only one device working

[mfoolb]

Sure not, as I said. You need to install Intel OpenCL runtime for CPU, this gives you a much better performance for AMD CPU (and also faster than pocl).

So, the forementioned link doesn't refer to the installation of the Intel OpenCL runtime for CPU?

Should I start from here: https://github.com/intel/compute-runtime/releases and try to compile for my kernel? Are there ubuntu 4.15 source/packages anywhere?

Thanks.