7d0b1d5695
The ray tracer is compute-bound and the three existing benches only cover alloc / megamorphic-dispatch / collections. Add three axes the epic needs to judge itself holistically: - mono-dispatch: monomorphic protocol dispatch. Its jolt/JVM ratio (~110x) is *worse* than megamorphic (~76x) — the JVM inline-caches a runtime-monomorphic call site to near-free while jolt does a full registry dispatch (devirt only fires on statically-proven receivers). Points at the call-site inline cache. - mandelbrot: pure float compute, no alloc/dispatch. The floor at ~15x — native arith already gets close to the JVM. - fib: recursion, call + integer-arith overhead. run.sh gains JVM=1, which runs each bench on JVM Clojure too and prints the jolt/JVM ratio. collections sized up now that the map is a HAMT (jolt-684u). README documents the axes and the current scorecard. Co-authored-by: Yogthos <yogthos@gmail.com>
68 lines
3.7 KiB
Markdown
68 lines
3.7 KiB
Markdown
# jolt benchmark suite
|
||
|
||
Benchmarks that isolate the workload axes jolt's optimizing passes target. The
|
||
ray tracer (`examples/ray-tracer`) is **float-compute-bound** — its time is
|
||
irreducible algorithmic math (hit-testing + transcendentals), and devirt,
|
||
allocation removal, and type-proving all measured **flat** on it. So it can't
|
||
tell us whether those passes work. These benchmarks make each pass's target
|
||
workload the *dominant* cost.
|
||
|
||
Reference: the cross-language suites these draw from —
|
||
[Are We Fast Yet?](https://github.com/smarr/are-we-fast-yet) (Marr et al., DLS '16)
|
||
and the [Computer Language Benchmarks Game](https://benchmarksgame-team.pages.debian.net/benchmarksgame/).
|
||
The benchmarks are portable Clojure, so they also run on JVM Clojure for an
|
||
absolute reference.
|
||
|
||
## Benchmarks
|
||
|
||
| Benchmark | Axis | Pass it exercises | Source |
|
||
|---|---|---|---|
|
||
| `binary-trees` | allocation / GC pressure (escaping short-lived records) | jolt-15jq scalar-replace, jolt-8flj escape analysis | CLBG |
|
||
| `dispatch` | polymorphic (**megamorphic**) protocol dispatch | jolt-41m devirt, inline-cache | AWFY-style |
|
||
| `mono-dispatch` | **monomorphic** protocol dispatch (devirt/inline-cache *can* fire) | jolt-41m devirt, jolt-ez5h inline-cache | AWFY-style |
|
||
| `collections` | persistent map/vector churn (HAMT / 32-way tries) | persistent structures (jolt-684u/0hbr), transients | CLBG k-nucleotide-style |
|
||
| `mandelbrot` | pure float compute (tight arith loops, no alloc/dispatch) | jolt-3pl native arith, loop codegen | CLBG |
|
||
| `fib` | recursion: function-call + integer-arith overhead | jolt-3pl native arith, jolt-826 small-fn inlining | CLBG |
|
||
|
||
What the ray tracer does **not** capture and these do: allocation as the
|
||
bottleneck (~7% there), megamorphic *and* monomorphic dispatch (its dispatch is
|
||
monomorphic and cheap), persistent-collection throughput (it uses fixed records,
|
||
no collections in the hot loop), and isolated compute/call overhead.
|
||
|
||
Planned additions: Richards / DeltaBlue (heavier OO dispatch), NBody (float
|
||
control with record state), k-nucleotide proper.
|
||
|
||
## Holistic scorecard
|
||
|
||
`JVM=1 bench/run.sh` runs each benchmark on jolt **and** JVM Clojure and prints
|
||
the jolt/JVM ratio — the epic's (jolt-ffn) absolute-reference scorecard. As of
|
||
the broadening (2026-06-16), ratios cluster by axis:
|
||
|
||
- **pure compute** (`mandelbrot`) is the floor, ~15× — native arith (jolt-3pl)
|
||
already gets jolt closest to the JVM.
|
||
- **collections** ~28×, **fib** ~37×.
|
||
- **dispatch** ~75× (megamorphic), and `mono-dispatch` is *worse* (~110×): the
|
||
JVM inline-caches a runtime-monomorphic call site to near-free, while jolt does
|
||
a full registry dispatch regardless (devirt only fires on *statically* proven
|
||
receivers, which `reduce` over a vector doesn't give). This is the signal for
|
||
the call-site inline cache (jolt-ez5h).
|
||
- **allocation** (`binary-trees`) is the widest gap — but also the most inflated
|
||
by host memory pressure, so read it as "alloc is the worst axis," not a precise
|
||
multiple. Numbers are machine-specific; regenerate with `JVM=1 bench/run.sh`.
|
||
|
||
## Running
|
||
|
||
```sh
|
||
jpm build && export PATH="$PWD/build:$PATH"
|
||
bench/run.sh # whole-program optimization on (default)
|
||
JOLT_WHOLE_PROGRAM=0 bench/run.sh # WP off, to measure what WP buys
|
||
bench/run.sh binary-trees 16 # one benchmark, custom size
|
||
```
|
||
|
||
## A/B against a change
|
||
|
||
To measure a pass, run the suite on `main`, then on the branch, back to back
|
||
(same machine, quiet) — the protocol used for `test/bench/core-bench.janet` and
|
||
the ray tracer. Each benchmark prints `runs: [...]` and `mean: N ms`; compare
|
||
the means. A pass is worth landing when it moves a benchmark whose axis it
|
||
targets, even if the ray tracer stays flat.
|