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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