vkcheck

vkcheck [library]

vkcheck reports whether this machine's GPU can run Janas-LLM's GPU backend, and how. For every Vulkan device it prints each requirement with the driver's answer, then the decision the engine would take (the same rules as `src/llm/gpu.c`). If a device is taken, it runs three short tests on that device:zero-copy: this process's memory imported by the GPU (the host-allocation import extension), read and written by a shader, with the CPU seeing the result and no copy. An integrated GPU (Apple's under MoltenVK too) is taken only this way.dot: the integer dot product of four signed bytes against the CPU's, plus a rough rate. Janas-LLM's quantized products are made of that operation; a driver may emulate it.float: fused multiply-add rounded once, a precise a times b plus c twice, and a precise sum in the order written (what keeps the GPU's results the CPU's to the bit, and what a fast-math compiler breaks). Whether subnormals survive is printed for information.The engine's choice is a discrete GPU first, then an integrated one. The optional library is loaded instead of the usual search (`libvulkan.so.1` then `libvulkan.so` on Linux; the Vulkan loader or MoltenVK on macOS; `vulkan-1.dll` on Windows).`./build.sh` writes the program to `bin/` from `tools/vkcheck.c`, next to janas-chat. It is also meant to be compiled on its own where Janas does not build yet.

library

Path to a Vulkan loader or MoltenVK. With none, the platform defaults are tried in order.

JANAS GPU DEVICE

`discrete` or `integrated`: restrict which kind of GPU the engine (and this tool) would pick. Same meaning as in Janas-LLM.

Wanted subgroup size (default 8). Used when the device lets the size be chosen.

Exit 0 when the engine would take a GPU and every test passes. Exit 1 when there is no Vulkan library, no instance, no GPU, no GPU the engine would take, or a test failed (the last case prints `some test FAILED: tell the project, with this output`). Exit 2 when the binary was compiled without the Vulkan headers (`vkcheck: built without the Vulkan headers`). The Vulkan library is loaded at run time. Built into `bin/` by Janas's `./build.sh`. It is not a separate package. Attach the output to a Janas hardware report.

vkcheck ships with Janas, written by Maurizio "camauri" Cammalleri (first public release September 2026, GNU GPL 3 or later). `docs/hardware.md` names it as the check for whether a GPU can run the GPU backend, including on machines where the rest of Janas does not build.

gpu_check(1), janas-bench(1), janas-chat(1), vulkaninfo(1), janas-get(1)

Source code · Documentation