Offline autotune configs

FlyDSL can serve a previously tuned config without benchmarking. This extends the direct-JIT autotuner with one opt-in argument:

@flyc.jit
def launch(x, out, N: fx.Constexpr[int], BLOCK: fx.Constexpr[int]):
    ...


tuned = autotune(
    configs=[Config(BLOCK=128), Config(BLOCK=256)],
    key=["N"],
    default=lambda x, out, N: Config(BLOCK=256),
    artifact_name="my_kernel",
)(launch)

artifact_name enables lookup when FLYDSL_AUTOTUNE_CONFIG_DIR is set. Normal calls use the first available source:

searched winner cache -> matching artifact -> default -> search

FLYDSL_AUTOTUNE=1 bypasses those serving decisions, searches the existing configs, updates the scratch winner cache, and atomically writes an artifact. A normal fallback search updates only the scratch cache. While artifact lookup is active, scratch winners use the same device descriptor so a same-architecture product cannot shadow the matching artifact.

Identity and compatibility

Artifact identity is the stable artifact_name, the declared key values, and the call device’s product name, target architecture, and compute-unit count. Use a globally unique name for each kernel/config schema. The JSON is self-describing; its filename is an identity digest.

The declared key is the single owner of portable tuning axes. Include every shape, dtype, layout, or mode that can change the winner. Keep structural knobs as JIT Constexpr parameters on the existing entry point; offline tuning does not need a build factory or a second key callback.

Artifacts intentionally do not include a compiler or kernel-source fingerprint. Treat them as reviewed deployment inputs and retune after a compiler, kernel, compile-hint, or search-space change that can affect the winner.

Failure behavior

Missing, unreadable, mismatched, or structurally invalid artifacts are ignored, and normal lookup continues to the default or search path. Artifact config values cannot overwrite arguments supplied by the caller or declared key axes. Values must preserve their types when encoded as JSON. Config.pre_hook is process-local code, so it blocks forced artifact generation.

Once a matching artifact has been accepted, its compile, launch, and runtime errors propagate normally; FlyDSL does not hide them by retrying the default. If forced generation cannot establish a device identity or write its artifact, it fails clearly without caching the winner.

Generate deployment artifacts on the intended GPU under controlled benchmark conditions. CI should verify deterministic emit-and-load behavior, not commit a winner selected from noisy shared-runner timing.