This specific component is a SPIR-V backend for Rust. In practice, how you use this is you use a native API (Vulkan), give it your generated SPIR-V program, and

This specific component is a SPIR-V backend for Rust. In practice, how you use this is you use a native API (Vulkan), give it your generated SPIR-V program, and it "runs it" using its own semantics. This is a combination of a userspace API talking to a kernel driver, and the kernel driver using a combination of IN/OUT instructions (unlikely) and memory-mapped I/O (much more likely) to talk to the GPU. The actual details of the communication is documented by some IHVs, either through PDFs or source code. Normally, the CPU doesn't wait for programs to complete, but instead, the GPU driver has a list of tasks to run (a "command buffer") that it itself can schedule across many different pieces of hardware, and a combination of the driver and GPU itself determine scheduling, execution, and so on. Note that there's still a lot of work for the driver to do, including managing the device's memory (textures, buffers, so on), compiling any programs into machine language (similar to a JIT), and coordinating multiple different programs trying to use the GPU.