gpu_check

Compare Janas-LLM GPU matvecs with the CPU, bit for bit

TLDR

Run every GPU product against the CPU (from a Janas build)

$ gpu_check

Touch n GiB first, like the expert cache

$ GPU_CHECK_BIG_GB=[8] gpu_check

Copy weights through the GPU's own memory (discrete-card path)

$ JANAS_GPU_COPY=1 gpu_check

gpu_check runs every kind of product Janas-LLM's GPU backend takes and compares each result with the CPU's, bit for bit. It is the check `docs/hardware.md` asks for when a GPU gives wrong answers while JANAS GPU=0 is right: the last line says `ok` or `FAILED`, with the shapes that differ above it. A run takes a minute or two.It walks random matrices in the types the backend implements (Q4-K, Q5-K, Q6-K, Q6-K bit planes at three levels, Q8-0, the 32- and 64-weight blocks, the 1- and 2-bit IQ types, and bf16 weights on float vectors), several shapes, vector counts, and strides, including rows that end inside a group of 256. The fast prompt is turned off for the run so rounding does not hide a mismatch. When JANAS GPU COPY is set, weights go through the GPU's own memory, as on a card that does not share host RAM.With no usable GPU it prints `gpu_check: no GPU (...), skipped` and exits 0. Import or comparison failures exit 1.`./build.sh` writes the program to `bin/` from `tests/gpu_check.c`. Release packages from 24 October 2026 include it. There are no command-line flags; extra arguments are ignored.

CONFIGURATION

JANAS GPU COPY

Set to 1 to copy weights onto the GPU as a discrete card does, then compute there.

GPU CHECK BIG GB

If set to a positive integer n, allocate and touch n GiB before the tests, similar to the engine's expert cache.

GPU CHECK ENGINE

If set, use a 12-thread pool pinned like the engine (CPUs 0-11). Default is 4 unpinned threads.

GPU CHECK PIN

With GPU CHECK ENGINE, also pin the calling thread to CPU 0.

CAVEATS

Needs a Janas build with GPU support (Vulkan headers and a new enough glslang). No GPU is a skip, not a failure. A failed comparison prints at most ten mismatch lines, then `FAILED` on the summary. The summary also names the GPU and its subgroup size. Built into `bin/` by Janas's `./build.sh`. It is not a separate package. Attach the output to a Janas hardware report.

HISTORY

gpu_check ships with Janas, written by Maurizio "camauri" Cammalleri (first public release September 2026, GNU GPL 3 or later). It entered the binary packages with the 24 October 2026 release so testers can tell a bad GPU product from some other fault.

RESOURCES

Source code · Documentation