ci: add GitHub Actions workflow - #1
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- precommit job on macos-14 (arm64): runs mix precommit on every PR and push to main. Caches deps, _build, and the MLX prebuilt archive (~100 MB) so subsequent runs don't re-download. - soak job: nightly-only (17 3 UTC), runs the :soak tag. - concurrency group cancels superseded runs on the same ref.
ausimian
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Apr 14, 2026
A pure-C++ microbenchmark on MLX 0.25.1 / Apple Silicon GPU shows the
fusion win on a Qwen3-0.6B-shaped transformer block is 1.04x-1.07x
(GPU) and a regression on CPU (0.82x-0.88x) — well below the PLAN's
1.20x gate. A sanity workload (pure 8-op elementwise chain) in the
same harness shows 2.78x GPU / 1.47x CPU, so the measurement is
trustworthy — the limiting factor is that MLX compile doesn't fuse
matmul with surrounding elementwise ops, and transformer inference is
matmul-dominated. Fusion wins are confined to RMSNorm / softmax /
SwiGLU neighbourhoods, a small fraction of block runtime.
The BEAM-integrated compile path could not exceed this C++ ceiling,
so Phase 2 (approach review) and Phase 3 (implementation) were not
built.
Retained as permanent fixtures so the decision can be re-measured
against future MLX releases without rebuilding the harness:
- bench/native/compile_microbench.cpp — transformer block + sanity
elementwise chain, both timed compiled vs uncompiled.
- lib/mix/tasks/bench.native.ex — `mix bench.native` invokes the
new `bench-native` Makefile target with the same env elixir_make
sets, reusing the project's pinned MLX without a second fetch.
Supports --seq / --warmup / --iters via `mix bench.native -- ...`.
- Makefile: `bench-native` target, produces
$(BUILD_DIR)/compile_microbench and runs it.
- bench/compile_microbench.md — results table + reproduction.
PLAN.md: M6 section rewritten to record the drop with the measurement;
core design decision #1 and the M5 footnote updated to match.
Emily.Compiler moduledoc note reframed.
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Summary
macos-14) — Emily is Apple-Silicon-only, so no Linux matrixprecommitjob on every PR and push to main:mix deps.get && mix precommitsoakjob scheduled nightly (03:17 UTC): runsmix test --only soakdeps/,_build/Test plan