Brummel
de4399df37
Audit Step 2 (regression scripts) blocked at exit 2 on bench/check.py
— the latency arms produced lines=0 because their fixtures rely on
`(app print N)` to deliver one newline per sample, but the
io/print_str byte-faithful change (commit 26fb345, closes #29)
stopped trailing newlines from appearing in the polymorphic
print path. Pre-existing infrastructure failure, NOT iter-caused;
fix is one \n insertion per print site in both bench_latency_*.ail
fixtures, behaviour-preserving for any other consumer.
With infra unblocked, bench/check.py reported exit 1 on
latency.explicit_at_rc.p99_us (+42% then +65% across two
back-to-back runs) and the cognate p99_over_median. Median +1.3%,
implicit-arm-control all green. Dispatched bencher for
hypothesis-driven characterisation; the report (6 back-to-back
invocations, recorded per-invocation p99 + within-invocation
[lo, hi] spread) is unambiguous:
- explicit-arm p99_us cv = 18.6% across invocations
- explicit-arm median_us cv = 0.37% (steady-state allocator signal)
- implicit-arm p99_us cv = 2.9% (the control — no co-firing)
- 4 of 6 invocations would trip the 25% gate even though the
underlying mean (~329 µs) is closer to baseline (259.9 µs) than
to the worst observed (418 µs)
Structurally identical to the 2026-05-20 recalibration that
removed max_us and p99_9_us (iter bench-harness-recalibration.1,
Gitea #15 / #16) — see docs/specs/0047-bench-harness-recalibration.md.
The 2026-05-20 gamble was that p99 was still allocator-attributable
on a quiet developer machine; that gamble has now failed on the
explicit arm.
Ratify path: removed latency.explicit_at_rc.p99_us and
latency.explicit_at_rc.p99_over_median from baseline.json. The
explicit arm gates only on median_us going forward — the only
metric whose cv (0.37%) actually reflects allocator behaviour
rather than OS jitter. The implicit-arm p99 + p99_over_median
stay — they are stable (cv 2.9%) and provide the contrast that
lets future audits distinguish a real allocator regression from
machine-state jitter.
This is a ratify, not an intentional baseline movement caused by
prep.3: the kernel-extension-mechanics work touches schema +
checker + workspace-load — no codegen-runtime change that could
plausibly affect RC tail latency. The decision is forward-looking
metric removal (per honesty-rule: a regression gate that fires
4 of 6 times on byte-identical code is not a gate, it is a
random-event generator).
Bench results post-ratify: exit 0 across all three scripts
(bench/check.py 34 metrics 0 regressed; bench/compile_check.py 24
metrics 0 regressed; bench/cross_lang.py 25 metrics 0 regressed).
Architect drift items (8 enumerated) will be addressed in a
separate consolidated tidy iteration; this commit only closes the
bench gate.
170 lines
5.8 KiB
Plaintext
170 lines
5.8 KiB
Plaintext
; Latency-distribution bench fixture — explicit-mode variant.
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;
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; Companion to bench_latency_implicit. Same algorithm, with
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; `(borrow T)` / `(own T)` annotations so that under --alloc=rc the
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; codegen emits proper inc/dec instrumentation: the persistent tree
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; cache is borrowed (no inc/dec on pin_root's hot path), the per-op
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; IntList is owned by sum_list (param drop at fn return frees the
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; chain). The drop-iterative annotation on IntList keeps the per-op
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; deallocation O(1)-stack regardless of list length.
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;
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; This is the "RC-fair" arm of the latency bench; together with
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; bench_latency_implicit (the implicit-mode control arm at rc) it
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; tests the hypothesis "RC under explicit-mode has p99
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; per-operation latency within a small constant factor of the
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; median, even under continuous alloc pressure with a large
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; persistent live working set".
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;
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; Workload (must match bench_latency_implicit's parameters exactly
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; for the comparison to be fair):
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; - Live cache: balanced binary tree of depth 19 (524_287 nodes,
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; ~16 MB), borrowed throughout the loop.
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; - Per-op: build a CHUNK_LEN-cell IntList of 0..CHUNK_LEN-1, sum
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; it, drop it. CHUNK_LEN, NUM_OPS, PRINT_K hardcoded to match
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; the implicit variant.
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; - Same stdout shape: one READY (8888), N_PRINT timing markers
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; each containing the per-op sum (validatable, always equal),
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; one DONE (9999).
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(module bench_latency_explicit
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(data Tree
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(doc "Balanced binary tree, 32-byte cells. Borrowed across the bench loop; tree-depth recursion at scope close is bounded (depth 19) so no drop-iterative needed.")
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(ctor TLeaf)
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(ctor TNode (con Int) (con Tree) (con Tree)))
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(data IntList
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(doc "Singly-linked Int list. Per-op chains are CHUNK_LEN long; (drop-iterative) keeps Own-param drop O(1) stack regardless of length.")
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(ctor LNil)
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(ctor LCons (con Int) (con IntList))
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(drop-iterative))
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; ---------- Live cache: balanced tree of given depth ----------
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(fn build_tree
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(doc "Build a balanced tree of given depth, every value = 1. Returns owned Tree; main holds it across the loop and the final drop fires at main's scope close.")
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(type
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(fn-type
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(params (con Int))
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(ret (own (con Tree)))))
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(params depth)
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(body
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(if (app eq depth 0)
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(term-ctor Tree TLeaf)
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(term-ctor Tree TNode
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1
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(app build_tree (app - depth 1))
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(app build_tree (app - depth 1))))))
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(fn pin_root
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(doc "Constant-time tree liveness pin — read root tag, return 1 (TNode) or 0 (TLeaf). Borrows t so the persistent cache is not inc/dec'd on every op.")
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(type
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(fn-type
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(params (borrow (con Tree)))
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(ret (con Int))))
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(params t)
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(body
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(match t
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(case (pat-ctor TLeaf) 0)
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(case (pat-ctor TNode v l r) 1))))
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; ---------- Per-op work: build/sum an N-cell list ----------
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(fn cons_n_acc
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(doc "Tail-recursive list builder. Returns owned chain; caller is sum_list which owns and drops it.")
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(type
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(fn-type
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(params (con Int) (own (con IntList)))
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(ret (own (con IntList)))))
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(params n acc)
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(body
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(if (app eq n 0)
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acc
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(tail-app cons_n_acc
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(app - n 1)
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(term-ctor IntList LCons (app - n 1) acc)))))
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(fn cons_n
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(doc "Build [0,1,...,n-1] :: IntList. Returns owned chain.")
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(type
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(fn-type
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(params (con Int))
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(ret (own (con IntList)))))
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(params n)
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(body
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(app cons_n_acc n (term-ctor IntList LNil))))
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(fn sum_list_acc
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(doc "Tail-recursive sum. Owns xs; consumes it via the LCons arm's t binder (move-into-tail-call).")
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(type
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(fn-type
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(params (own (con IntList)) (con Int))
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(ret (con Int))))
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(params xs acc)
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(body
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(match xs
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(case (pat-ctor LNil) acc)
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(case (pat-ctor LCons h t)
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(tail-app sum_list_acc t (app + acc h))))))
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(fn sum_list
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(doc "Sum every element. Owns xs, hands it to sum_list_acc which consumes it.")
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(type
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(fn-type
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(params (own (con IntList)))
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(ret (con Int))))
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(params xs)
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(body
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(app sum_list_acc xs 0)))
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(fn one_op
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(doc "One bench operation: build+sum a fresh CHUNK_LEN-cell list, pin the tree's root, return their sum so the value chain stays observable. Tree is borrowed; no inc/dec on the hot path against the persistent cache.")
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(type
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(fn-type
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(params (con Int) (borrow (con Tree)))
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(ret (con Int))))
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(params chunk_len t)
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(body
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(app + (app sum_list (app cons_n chunk_len)) (app pin_root t))))
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; ---------- Bench loop ----------
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(fn loop
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(doc "Tail-recursive bench loop. Tree is borrowed across all iterations.")
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(type
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(fn-type
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(params (con Int) (con Int) (con Int) (con Int) (borrow (con Tree)))
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(ret (con Unit))
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(effects IO)))
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(params remaining print_countdown chunk_len print_k t)
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(body
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(if (app eq remaining 0)
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(seq (app print 9999) (do io/print_str "\n"))
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(if (app eq print_countdown 0)
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(seq
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(seq (app print (app one_op chunk_len t)) (do io/print_str "\n"))
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(tail-app loop
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(app - remaining 1)
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(app - print_k 1)
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chunk_len
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print_k
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t))
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(let _v (app one_op chunk_len t)
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(tail-app loop
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(app - remaining 1)
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(app - print_countdown 1)
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chunk_len
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print_k
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t))))))
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(fn main
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(doc "Top-level: build tree, signal READY (8888), run loop, signal DONE (9999 emitted by loop).")
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(type (fn-type (params) (ret (con Unit)) (effects IO)))
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(params)
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(body
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(let t (app build_tree 19)
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(let _root (app pin_root t)
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(seq
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(seq (app print 8888) (do io/print_str "\n"))
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(app loop 20000 0 500 20 t)))))))
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