← Lab
gemvthreads
null resultC++ · NEON / Apple M4Systems & data structuresJuly 6, 2026
the question
Decode is memory-bandwidth-bound -- so does the CPU quantized matmul stop scaling once a few threads saturate memory?
what came out
No, the surprise. The CPU GEMV scales near-linearly with cores and is compute-bound (implied bandwidth well below the ~216 GB/s ceiling); cache-resident and memory-resident matrices scale the same. The bandwidth wall is a system-level property, not in this kernel. All three pre-registered predictions held.
method & receipts
- Result: null result — an honest negative, reported as it came out.
- Pre-registered — the prediction was written down and committed before the run.
- Reproducible — one script re-runs the whole thing from scratch.
- Independently reviewed — an adversarial review pass, kept in the repo.
- Machine-readable claims — every reported number, in a checkable file.
- Tested — a correctness/benchmark suite ships alongside the code.
→ read the code and re-run it
github.com/v-code01/gemvthreads