bench: real black_box barrier + three-signal growth-curve gate
Adds el_black_box (inline asm, +r constraint, memory clobber) and runtime/elbench.el: a growth-curve classifier that gates time AND allocation-count AND allocation-bytes, failing if any exceeds its declared curve. Refusal is a first-class verdict. The classifier REFUSES rather than classifying when the largest measurement is below the floor, or when a series is hard-flat across an 8x input range -- the shape produced when the optimiser deletes the work. Reporting O(1) there would be a confident answer with nothing behind it. Disagreeing ratios report INDETERMINATE rather than a guess. Deviation from DESIGN.md 6.2, stated in the source: uses consecutive ratios on a mandated geometric sweep rather than least-squares over candidate curves. Ratios are directly interpretable on a doubling sweep and need no floating point; the cost is weaker O(n) vs O(n log n) separation, reported as an ambiguous band rather than guessed. Documents the counter scope limit: engram_*.c and libcurl malloc are NOT tracked, so a flat curve over engram/HTTP-dominated work is not evidence of anything. 13 tests prove the classifier against real measured series from fitprobe.el -- including that an accumulator's allocation COUNT is linear while its bytes are quadratic, and that el #132's pure-CPU shape reads FLAT on both allocation signals and is caught only by time.
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Neuron
@@ -18522,6 +18522,26 @@ el_val_t engram_pool_stats_json(void) {
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el_val_t el_alloc_count(void) { return (el_val_t)(int64_t)_el_alloc_count; }
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el_val_t el_alloc_bytes(void) { return (el_val_t)(int64_t)_el_alloc_bytes; }
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/* el_black_box — optimisation barrier for benchmark bodies.
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*
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* WHY THIS IS NOT OPTIONAL. A benchmark whose result is unused is dead code,
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* and CONSUMING THE RESULT IS NOT SUFFICIENT: clang recognises loop idioms and
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* closes them to arithmetic. A nested `total = total + 1` loop measured at
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* 0 microseconds for every n while returning a numerically correct n*n --
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* the answer was right and the work never happened.
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*
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* That is the same failure shape as a test that never ran reporting pass. The
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* harness must own the barrier rather than trusting the benchmark author to
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* defeat the optimiser.
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*
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* The constraint "+r" forces the value through a register the compiler must
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* treat as both read and written by opaque code; the "memory" clobber stops
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* loads and stores being reordered across it or elided. Emits no instructions. */
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el_val_t el_black_box(el_val_t v) {
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__asm__ __volatile__("" : "+r"(v) : : "memory");
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return v;
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}
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el_val_t el_peak_rss(void) {
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struct rusage ru;
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if (getrusage(RUSAGE_SELF, &ru) != 0) return (el_val_t)0;
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@@ -1022,6 +1022,7 @@ el_val_t el_mem_check(void);
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el_val_t el_alloc_count(void);
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el_val_t el_alloc_bytes(void);
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el_val_t el_peak_rss(void);
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el_val_t el_black_box(el_val_t v);
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/* Semantic retrieval surface. NOT interchangeable with engram_search_json,
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* which is lexical by design — see the note at the definition. */
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@@ -0,0 +1,244 @@
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// runtime/elbench.el — growth-curve classifier and complexity gate.
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//
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// Given a geometric sweep of input sizes and the measurements taken at each,
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// classify the growth curve and decide whether it violates a declared bound.
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//
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// ── Why this exists ──────────────────────────────────────────────────────────
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//
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// Constant-factor regressions are annoying. Complexity regressions are outages.
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// An O(n) lookup inside an O(n) loop is invisible at n=100 in a unit test and
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// catastrophic at n=100000 in production. el #132 was exactly that: a strlen()
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// inside a per-character accessor, quadratic, shipped for months.
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//
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// ── THREE signals, not one ───────────────────────────────────────────────────
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//
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// The gate fits time AND allocation-count AND allocation-bytes, and fails if
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// ANY of them exceeds its declared curve. This is not belt-and-braces; each
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// signal is blind to a real defect class the others catch:
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//
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// * A copy-on-write accumulator rebuilding its buffer allocates ONCE per
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// iteration — count is exactly linear — while bytes go quadratic.
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// Count alone passes it.
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// * el #132's strlen-per-character is pure CPU and allocates NOTHING.
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// Both allocation signals read FLAT. Only time catches it.
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//
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// The deterministic signals (count, bytes) are preferable where they apply:
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// no statistics, correct on the first run, machine-independent. They are
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// simply not sufficient.
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//
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// ── SCOPE LIMIT — read this before trusting a flat curve ─────────────────────
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//
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// The allocation counters track EL-LEVEL allocation only: strings, ElList and
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// ElMap bodies, their backing arrays, copy-on-write clones, and the realloc
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// growth path. malloc inside engram_*.c and inside libcurl is NOT counted.
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//
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// A flat allocation curve over a workload dominated by engram or HTTP calls is
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// therefore NOT evidence of anything. It means "no El-level allocation growth",
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// not "no allocation growth". Gate El-level complexity with this; do not read
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// third-party memory behaviour into it.
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//
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// ── Classification method ────────────────────────────────────────────────────
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//
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// Sizes must form a geometric sweep (each n double the last). On such a sweep
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// the ratio between consecutive measurements IS the growth exponent, directly:
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//
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// O(1) -> 1.0 O(log n) -> ~1.1 O(n) -> 2.0
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// O(n log n) -> ~2.2 O(n^2) -> 4.0 O(n^3) -> 8.0
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//
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// DEVIATION FROM DESIGN.md 6.2, stated plainly: that section specified Google
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// Benchmark's one-parameter least-squares fit over candidate curves. This uses
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// consecutive ratios instead. The sweep is mandated geometric either way, and
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// on a geometric sweep ratios are directly interpretable and need no floating
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// point. The cost is weaker separation between O(n) and O(n log n), which is
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// reported honestly as an ambiguous band rather than guessed at. Least-squares
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// remains the better answer if that band ever needs to be resolved.
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//
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// All arithmetic is fixed-point, scaled by 1000 ("milli-ratio"), so a ratio of
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// 2.0 is 2000. El values are int64; this avoids float-in-list handling.
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// Curve identifiers. Ordered by growth — the ordering IS the comparison used
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// by the gate, so an index comparison decides "worse than declared".
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// 0 = O(1) 1 = O(log n) 2 = O(n) 3 = O(n log n) 4 = O(n^2) 5 = O(n^3)
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fn elb_curve_name(c: Int) -> String {
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if c == 0 { return "O(1)" }
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if c == 1 { return "O(log n)" }
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if c == 2 { return "O(n)" }
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if c == 3 { return "O(n log n)" }
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if c == 4 { return "O(n^2)" }
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if c == 5 { return "O(n^3)" }
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return "O(?)"
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}
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fn elb_curve_from_name(s: String) -> Int {
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if str_eq(s, "O(1)") { return 0 }
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if str_eq(s, "O(log n)") { return 1 }
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if str_eq(s, "O(n)") { return 2 }
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if str_eq(s, "O(n log n)") { return 3 }
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if str_eq(s, "O(n^2)") { return 4 }
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if str_eq(s, "O(n^3)") { return 5 }
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return -1
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}
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// elb_classify_ratio — map a milli-ratio-per-doubling onto a curve.
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//
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// Bands are deliberately wide at the top (a quadratic measured at 3.4x is
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// still a quadratic) and deliberately overlap-averse at the bottom, where a
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// misclassification between O(1) and O(log n) matters least.
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fn elb_classify_ratio(milli: Int) -> Int {
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if milli < 1300 { return 0 }
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if milli < 1700 { return 1 }
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if milli < 2400 { return 2 }
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if milli < 3200 { return 3 }
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if milli < 6000 { return 4 }
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return 5
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}
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// elb_ratio — milli-ratio between two consecutive measurements.
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// Returns -1 when the earlier measurement is zero (ratio undefined).
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fn elb_ratio(prev: Int, cur: Int) -> Int {
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if prev <= 0 { return -1 }
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return (cur * 1000) / prev
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}
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// ── The measurement floor ────────────────────────────────────────────────────
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//
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// A benchmark whose largest measurement is at or near zero has not been
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// measured. Reporting it as O(1) would be a confident answer with nothing
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// behind it — the same failure as a test that never ran reporting pass, and
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// exactly what happened when clang closed a nested loop to a multiply and the
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// harness read 0 microseconds at every n.
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//
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// So: REFUSE. Never classify below the floor.
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fn elb_below_floor(vals: [Int], floor: Int) -> Bool {
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let n: Int = native_list_len(vals)
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let i: Int = 0
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let mx: Int = 0
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while i < n {
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let v: Int = native_list_get(vals, i)
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if v > mx { let mx = v }
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let i = i + 1
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}
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if mx < floor { return true }
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return false
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}
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// elb_implausibly_flat — a measurement that does not move across a sweep whose
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// input grew by 8x or more is not a flat curve, it is a broken measurement.
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// Genuine O(1) work still shows noise; a hard-flat series means the work was
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// optimised away, the timer has insufficient resolution, or the benchmark body
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// never executed.
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fn elb_implausibly_flat(vals: [Int]) -> Bool {
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let n: Int = native_list_len(vals)
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if n < 3 { return false }
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let first: Int = native_list_get(vals, 0)
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let last: Int = native_list_get(vals, n - 1)
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if first == 0 {
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if last == 0 { return true }
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return false
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}
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let r: Int = (last * 1000) / first
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if r < 1100 { return true }
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return false
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}
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// elb_spread_ok — do the consecutive ratios agree with each other?
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//
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// This is the ratio-method analogue of a normalised-RMS threshold. If the
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// doublings disagree wildly the data is noise, a cache cliff, or a phase
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// change, and the honest report is INDETERMINATE rather than a classification.
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fn elb_spread_ok(ratios: [Int]) -> Bool {
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let n: Int = native_list_len(ratios)
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if n < 2 { return true }
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let lo: Int = 999999
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let hi: Int = 0
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let i: Int = 0
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while i < n {
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let r: Int = native_list_get(ratios, i)
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if r >= 0 {
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if r < lo { let lo = r }
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if r > hi { let hi = r }
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}
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let i = i + 1
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}
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if lo <= 0 { return false }
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// Reject when the widest ratio is more than 2.2x the narrowest. That is
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// enough slack for real timing noise and tight enough to separate a clean
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// 2.0 series from a clean 4.0 series.
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if (hi * 1000) / lo > 2200 { return false }
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return true
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}
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// elb_ratios — consecutive milli-ratios across the sweep.
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fn elb_ratios(vals: [Int]) -> [Int] {
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let out: [Int] = native_list_empty()
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let n: Int = native_list_len(vals)
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let i: Int = 1
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while i < n {
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let out = native_list_append(out,
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elb_ratio(native_list_get(vals, i - 1), native_list_get(vals, i)))
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let i = i + 1
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}
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return out
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}
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// elb_mean_tail_ratio — mean of the LAST TWO ratios.
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//
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// The tail is used deliberately: asymptotic behaviour is what a complexity
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// bound claims, and the small-n end of any sweep is dominated by fixed
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// overhead. This is the same reason a benchmark harness discards warmup.
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fn elb_mean_tail_ratio(ratios: [Int]) -> Int {
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let n: Int = native_list_len(ratios)
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if n == 0 { return -1 }
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if n == 1 { return native_list_get(ratios, 0) }
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let a: Int = native_list_get(ratios, n - 1)
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let b: Int = native_list_get(ratios, n - 2)
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if a < 0 { return b }
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if b < 0 { return a }
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return (a + b) / 2
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}
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// ── Verdicts ─────────────────────────────────────────────────────────────────
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//
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// 0 PASS measured curve is at or below the declared bound
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// 1 FAIL measured curve is strictly worse than declared
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// 2 INDETERMINATE ratios disagree; data is noise or a phase change
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// 3 REFUSED below the measurement floor, or implausibly flat
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// 4 BETTER measured strictly better than declared (warn, not fail)
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fn elb_verdict_name(v: Int) -> String {
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if v == 0 { return "PASS" }
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if v == 1 { return "FAIL" }
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if v == 2 { return "INDETERMINATE" }
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if v == 3 { return "REFUSED" }
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if v == 4 { return "BETTER" }
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return "?"
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}
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// elb_gate — classify one signal against its declared bound.
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//
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// vals measurements, one per sweep point, in sweep order
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// expect declared curve index (see elb_curve_name)
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// floor minimum largest-measurement below which we refuse to classify
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fn elb_gate(vals: [Int], expect: Int, floor: Int) -> Int {
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if elb_below_floor(vals, floor) { return 3 }
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if elb_implausibly_flat(vals) { return 3 }
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let ratios: [Int] = elb_ratios(vals)
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if !elb_spread_ok(ratios) { return 2 }
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let m: Int = elb_mean_tail_ratio(ratios)
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if m < 0 { return 2 }
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let got: Int = elb_classify_ratio(m)
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if got > expect { return 1 }
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if got < expect { return 4 }
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return 0
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}
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// elb_measured_curve — the classified curve for a signal, or -1 if unclassifiable.
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fn elb_measured_curve(vals: [Int], floor: Int) -> Int {
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if elb_below_floor(vals, floor) { return -1 }
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if elb_implausibly_flat(vals) { return -1 }
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let ratios: [Int] = elb_ratios(vals)
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let m: Int = elb_mean_tail_ratio(ratios)
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if m < 0 { return -1 }
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return elb_classify_ratio(m)
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}
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