jolt/bench/README.md

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? (Marr et al., DLS '16) and the Computer Language Benchmarks Game. 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)	scalar-replace, escape analysis	CLBG
dispatch	polymorphic (megamorphic) protocol dispatch	devirt, inline-cache	AWFY-style
mono-dispatch	monomorphic protocol dispatch (devirt/inline-cache can fire)	devirt, inline-cache	AWFY-style
collections	persistent map/vector churn (HAMT / 32-way tries)	persistent structures, transients	CLBG k-nucleotide-style
mandelbrot	pure float compute (tight arith loops, no alloc/dispatch)	native arith, loop codegen	CLBG
fib	recursion: function-call + integer-arith overhead	native arith, 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

bench/run.sh compiles each benchmark to an optimized AOT binary (joltc build --direct-link --opt) and times it against JVM Clojure running the same portable source — the jolt/JVM scorecard. jolt's optimizing passes fire only in a build; joltc run -m is unoptimized, so the harness always builds.

Indicative ratios (M-series, single isolated run — numbers are machine-specific, regenerate locally). They cluster into two regimes:

benchmark	ratio	axis
mandelbrot	~8×	pure float compute
fib	~9×	call + integer arith
collections	~9×	persistent map/vector churn
dispatch	~130×	megamorphic protocol dispatch
binary-trees	~140×	escaping short-lived records (allocation/GC)
mono-dispatch	~330×	monomorphic protocol dispatch

• Compute (~8–9×) is the substrate floor: Chez is a native-compiling AOT Scheme, not a profiling JIT, so it can't match HotSpot on hot loops. Native arith already gets jolt closest here.
• Dispatch & allocation (~130–330×) are the architectural gaps. jolt does a full protocol-registry lookup on every call; the JVM inline-caches a runtime-monomorphic site to near-free — which is why mono-dispatch is worse than megamorphic. devirt only fires on statically proven receivers (which reduce/mapv over a heterogeneous vector never gives), so the passes don't engage; a call-site inline cache is the missing lever. binary-trees nodes escape into the tree, so scalar-replace can't remove them — this is GC pressure.
• The optimization passes move these benchmarks <10% vs the unoptimized run, so the gaps are not a missing-flag problem; they're the dispatch/GC/JIT-floor work.

Running

bench/run.sh                 # full suite + JVM scorecard
bench/run.sh fib             # one benchmark, default size
bench/run.sh fib 32          # one benchmark, custom size
NO_JVM=1 bench/run.sh        # jolt only (skip the JVM reference)

Needs Chez's kernel dev files (libkernel.a + scheme.h) and cc for the build, like jolt build; set JOLT_CHEZ_CSV to override the detected csv dir.

A/B against a change

To measure a pass, run the suite on main, then on the branch, back to back (same machine, quiet). 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.