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hipfire-kernel-tuning

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Optimize hipfire HIP/compute kernels — pick a tuning lever (multi-row, K-tile depth, prefetch, wave-size port, WMMA/MFMA, fused projections, ISA flags) and validate the win across the supported RDNA arch matrix. Use when you've identified a hot kernel, want to land a real perf win, and need to NOT regress on archs you don't have hardware for. Codifies the methodology from this repo's actual perf history — wave64 CDNA3 port (commit 4105035, 2× decode), nontemporal-load revert (34eb024, -13% caught only by clean-baseline bisect), gfx12 WMMA port (PR

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hipfire-kernel-tuning

Skill for landing real kernel perf wins in hipfire without breaking cross-arch portability or shipping a regression that the speed-gate catches but you talked yourself past. Codifies the empirical methodology that's actually worked across the gfx1010 → gfx1201 + gfx94x matrix.

When to use

  • A profiler / crate::profile timer flagged a hot kernel as the bottleneck and you want to pick the right lever.
  • You have a candidate optimization (multi-row variant, deeper K unroll, wave64 port, ISA flag) and need to validate it doesn't regress on the cross-arch matrix.
  • The speed-gate flagged a regression on a "should-be-no-op" refactor and you need the bisect / fresh-process recipe.
  • You have R9700 (or any new arch hardware) and want to write arch-specific fast paths beyond the canonical port.

Read these in order

  1. playbook.md — measure → root-cause → pick lever → validate → ship. The 6-step workflow with the gates each step has to clear. Start here.
  2. levers.md — catalog of optimization patterns hipfire actually uses (wave64 port, multi-row GEMV, K-tile depth, s_prefetch_data, WMMA/MFMA, fused projections, per-kernel hipcc flags). Each lever names the commits where it landed (or was reverted) so you can read the diff.
  3. cross-arch.md — dispatch routing rules. How to add a new fast path that wins on gfx1100 without regressing gfx1010 /gfx1030 /gfx1200 /gfx94x. The "no unreachable branches" rule and why predicate helpers (has_wmma_f16, has_dot2_f32_f16) exist.
  4. case-studies.md — five worked examples from the git log: wave64 CDNA3 port (+2× decode), nontemporal-load fake-win revert (−13% caught), prompt-shape recovery (+24% τ), k2x32 null result, WMMA C-mapping silent-corruption fix. Read these to calibrate what a real win looks like vs a measurement artifact.

Key rules

  • Trust the speed-gate, not your gut. Within-session A/B noise on gfx1100 is ±10–15%. A "+8% win" measured by editing code + re-running in the same shell is inside the noise band. Use scripts/probe_commits.sh <baseline> <candidate> for cross-process measurement.
  • Bisect against the committed baseline, not against your last bench run. This is how the nontemporal-load fake +2% got caught as an actual −13%. See case-studies.md §2.
  • Negative results ship too — if a lever LOOKS like it should win and doesn't, document it in the commit message with the hypothesis why. Future contributors save the same hours.
  • Cross-arch verify before merging. The speed-gate runs on the baseline arch (gfx1100 typically); your change still needs to not regress gfx1010/gfx1030 if the relevant codepath touches them. See cross-arch.md.

What's not in this skill

  • New arch ports — see .agents/skills/hipfire-arch-port/ instead. That skill covers porting an EXISTING kernel to a new GPU family. This skill covers MAKING an existing kernel faster on the archs it already runs on.
  • DFlash spec-decode tuning — those wins come from algorithm changes (n-gram cache, prompt shape, draft retraining), not kernel ISA work. See crates/hipfire-runtime/src/dflash.rs and the coherence-gate-dflash.sh battery.

Cross-references

  • docs/methodology/perf-benchmarking.md — the bench protocol (within-session noise band, stale-binary trap, prompt-md5 discipline).
  • docs/QUANTIZATION.md — MQ4/HF4 design
    • asym KV math; required reading before touching quant kernels. If this doc conflicts with AGENTS.md on MQ3/DFlash release status, treat AGENTS.md and current code as the fresher source.
  • docs/ARCHITECTURE.md — the dispatch layering + two-model-paths surface that constrains where new variants can plug in.
  • tests/speed-baselines/<arch>.txt — the committed perf floor per arch. The speed-gate compares against these.