Claude (sandbox)
d496914d40
Samples were taken only when maybe_preempt's cold block happened to fire in-site, so the interval between the last check and SiteGuard drop was discarded on every site entry. Measured live on the 24-core box: 22-29us lost per entry, a constant attribution efficiency of ~0.93-0.94, which under-reported every impact (+83.5% where theory says +100%; the observed shortfall fits 1/(1-pct*eff)-1 at both 25% and 50%). SiteGuard enter/drop now call site_transition(): leaving the target site flushes the pending interval into the ledger (sample-only, never spins, so safe under no-preempt regions); entering the target site re-arms the sample clock so pre-site time is never attributed (the symmetric over-attribution). Winner attribution is factored into attribute(), shared by the cold check and the flush, with the same interval clamps. Adds examples/causal_attrib_probe.rs (ground-truth in-site time vs ledger attribution, the probe that confirmed the leak) and the site_boundaries_flush_tail regression test (a site entry that never hits a cold check must still be attributed). Also gates causal_probe on smarm-causal in Cargo.toml - it never was, so featureless builds of the examples were broken.
391 lines
15 KiB
Rust
391 lines
15 KiB
Rust
//! Integration tests for `smarm-causal` — native causal profiling (RFC 007).
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//!
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//! Gated on the feature; run with:
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//! cargo test --test causal --features smarm-causal
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#![cfg(feature = "smarm-causal")]
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use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
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use std::sync::Arc;
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use std::time::Duration;
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/// Progress points count, and snapshots expose deltas by name.
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#[test]
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fn progress_point_counts() {
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smarm::init(smarm::Config::exact(1)).run(|| {
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let before = smarm::causal::progress_snapshot();
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let h = smarm::spawn(|| {
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for _ in 0..100 {
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smarm::progress!("units-a");
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}
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for _ in 0..7 {
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smarm::progress!("units-b");
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}
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});
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h.join().unwrap();
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let after = smarm::causal::progress_snapshot();
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let delta = |name: &str| {
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after.iter().find(|(n, _)| n == name).map(|(_, c)| *c).unwrap()
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- before
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.iter()
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.find(|(n, _)| n == name)
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.map(|(_, c)| *c)
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.unwrap_or(0)
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};
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assert_eq!(delta("units-a"), 100);
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assert_eq!(delta("units-b"), 7);
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});
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}
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/// Site guards nest and restore, and site identity is per-actor: observable
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/// from inside the actor and gone once the guard drops.
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#[test]
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fn site_guard_nesting_restores() {
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smarm::init(smarm::Config::exact(1)).run(|| {
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let h = smarm::spawn(|| {
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assert_eq!(smarm::causal::current_site_name(), None);
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{
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let _outer = smarm::causal_site!("outer");
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assert_eq!(
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smarm::causal::current_site_name().as_deref(),
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Some("outer")
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);
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{
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let _inner = smarm::causal_site!("inner");
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assert_eq!(
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smarm::causal::current_site_name().as_deref(),
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Some("inner")
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);
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}
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assert_eq!(
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smarm::causal::current_site_name().as_deref(),
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Some("outer")
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);
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}
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assert_eq!(smarm::causal::current_site_name(), None);
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});
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h.join().unwrap();
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});
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}
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/// The core Coz transposition: while an experiment targets site S with a
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/// nonzero speedup, work inside S grows the global delay ledger and credits
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/// itself; an actor *outside* S absorbs the difference (its per-actor ledger
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/// catches up to the global one) instead of running delay-free.
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#[test]
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fn virtual_speedup_ledger() {
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let global_out = Arc::new(AtomicU64::new(0));
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let absorbed_out = Arc::new(AtomicU64::new(0));
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let g_out = global_out.clone();
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let a_out = absorbed_out.clone();
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smarm::init(smarm::Config::exact(2)).run(move || {
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let stop = Arc::new(AtomicBool::new(false));
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// Bystander: never in the target site; must absorb injected delay.
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let stop2 = stop.clone();
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let out2 = a_out.clone();
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let bystander = smarm::spawn(move || {
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while !stop2.load(Ordering::Relaxed) {
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smarm::check!();
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out2.store(
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smarm::causal::my_absorbed_delay_cycles(),
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Ordering::Relaxed,
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);
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}
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});
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// Target: spins inside the experiment's site.
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let stop3 = stop.clone();
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let target = smarm::spawn(move || {
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let _g = smarm::causal_site!("hot-site");
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while !stop3.load(Ordering::Relaxed) {
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smarm::check!();
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}
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});
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let base = smarm::causal::global_delay_cycles();
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smarm::causal::begin_experiment_for_test("hot-site", 50);
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smarm::sleep(Duration::from_millis(200));
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g_out.store(
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smarm::causal::global_delay_cycles() - base,
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Ordering::Relaxed,
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);
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smarm::causal::end_experiment_for_test();
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stop.store(true, Ordering::Relaxed);
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bystander.join().unwrap();
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target.join().unwrap();
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});
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let global = global_out.load(Ordering::Relaxed);
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let absorbed = absorbed_out.load(Ordering::Relaxed);
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// The target's site work must have grown the ledger…
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assert!(global > 0, "global delay ledger never grew");
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// …and the bystander must have absorbed a meaningful share of it (it can
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// lag by a few check intervals; require half to be robust).
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assert!(
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absorbed >= global / 2,
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"bystander absorbed {absorbed} of {global} global delay cycles"
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);
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}
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/// The forgiveness rule must not leak: delay is forgiven on resume from a
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/// *park* (Coz's blocked-thread rule), but an actor that merely yields on
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/// timeslice expiry stays runnable and must PAY — its work rate has to drop
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/// while an experiment targets someone else. (Regression: forgiving on every
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/// resume made all bystanders delay-immune, so experiments moved nothing.)
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#[test]
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fn runnable_bystander_pays_delay() {
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let baseline = Arc::new(AtomicU64::new(0));
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let during = Arc::new(AtomicU64::new(0));
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let b_out = baseline.clone();
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let d_out = during.clone();
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smarm::init(smarm::Config::exact(1)).run(move || {
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let stop = Arc::new(AtomicBool::new(false));
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// Target: in-site spinner; grows the ledger while the experiment runs.
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let stop_t = stop.clone();
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let target = smarm::spawn(move || {
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let _g = smarm::causal_site!("pay-site");
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while !stop_t.load(Ordering::Relaxed) {
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smarm::check!();
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}
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});
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// Bystander: pure check!-loop — yields on slice expiry, never parks.
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let stop_b = stop.clone();
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let iters = Arc::new(AtomicU64::new(0));
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let iters2 = iters.clone();
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let absorbed = Arc::new(AtomicU64::new(0));
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let absorbed2 = absorbed.clone();
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let bystander = smarm::spawn(move || {
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while !stop_b.load(Ordering::Relaxed) {
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iters2.fetch_add(1, Ordering::Relaxed);
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smarm::check!();
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absorbed2.store(
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smarm::causal::my_absorbed_delay_cycles(),
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Ordering::Relaxed,
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);
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}
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});
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let window = |out: &AtomicU64| {
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let i0 = iters.load(Ordering::Relaxed);
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let t = std::time::Instant::now();
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smarm::sleep(Duration::from_millis(150));
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let rate =
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(iters.load(Ordering::Relaxed) - i0) as f64 / t.elapsed().as_secs_f64();
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out.store(rate as u64, Ordering::Relaxed);
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};
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window(&b_out);
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let d0 = smarm::causal::global_delay_cycles();
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smarm::causal::begin_experiment_for_test("pay-site", 50);
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window(&d_out);
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smarm::causal::end_experiment_for_test();
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let injected = smarm::causal::global_delay_cycles() - d0;
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stop.store(true, Ordering::Relaxed);
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target.join().unwrap();
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bystander.join().unwrap();
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// The never-parking bystander's ledger can only advance by actually
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// spinning (forgiveness requires a real park), so this is no longer
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// vacuous: most of the injected delay must have been paid for real.
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let a = absorbed.load(Ordering::Relaxed);
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assert!(injected > 0, "experiment injected nothing");
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assert!(
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a >= injected / 2,
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"bystander spun off {a} of {injected} injected cycles"
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);
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});
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let b = baseline.load(Ordering::Relaxed) as f64;
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let d = during.load(Ordering::Relaxed) as f64;
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// Time-shared single scheduler: target is on-CPU ~50% of wall, so a 50%
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// virtual speedup injects ~25% of wall — expected slowdown ×0.8 (measured
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// exactly that live); on real parallelism it's ×0.67. Either way <0.9.
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assert!(b > 0.0, "bystander never ran");
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assert!(
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d < b * 0.9,
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"runnable bystander did not pay: baseline {b:.0}/s, during experiment {d:.0}/s"
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);
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}
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/// A zero-percent experiment must inject nothing: the null experiment is the
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/// baseline Coz relies on, and it doubles as the overhead sanity check.
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#[test]
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fn zero_speedup_injects_nothing() {
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smarm::init(smarm::Config::exact(2)).run(|| {
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let stop = Arc::new(AtomicBool::new(false));
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let stop2 = stop.clone();
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let worker = smarm::spawn(move || {
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let _g = smarm::causal_site!("zero-site");
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while !stop2.load(Ordering::Relaxed) {
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smarm::check!();
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}
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});
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let before = smarm::causal::global_delay_cycles();
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smarm::causal::begin_experiment_for_test("zero-site", 0);
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smarm::sleep(Duration::from_millis(50));
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smarm::causal::end_experiment_for_test();
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let after = smarm::causal::global_delay_cycles();
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stop.store(true, Ordering::Relaxed);
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worker.join().unwrap();
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assert_eq!(after, before, "0% speedup must not grow the delay ledger");
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});
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}
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/// `impact_pct` computes the normalized throughput impact of a (site,
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/// speedup) cell against that site's own 0% baseline: injected virtual delay
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/// is removed from the divisor (Coz's normalization), so a bottleneck site
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/// shows positive impact and a fully-overlapped one shows ~zero.
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#[test]
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fn impact_from_synthetic_results() {
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use smarm::causal::{impact_pct, tsc_hz, ExperimentResult};
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let hz = tsc_hz();
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let secs = |s: f64| Duration::from_secs_f64(s);
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let cycles = |s: f64| (s * hz) as u64;
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let results = vec![
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// Baseline: 1000 units in 1s, nothing injected.
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ExperimentResult {
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site: "bottleneck".into(),
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speedup_pct: 0,
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duration: secs(1.0),
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deltas: vec![("units".into(), 1000)],
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injected_cycles: 0,
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},
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// Bottleneck at 50%: raw count unchanged, 0.5s injected
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// -> rate 1000/0.5 = 2x baseline -> +100%.
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ExperimentResult {
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site: "bottleneck".into(),
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speedup_pct: 50,
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duration: secs(1.0),
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deltas: vec![("units".into(), 1000)],
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injected_cycles: cycles(0.5),
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},
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ExperimentResult {
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site: "overlapped".into(),
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speedup_pct: 0,
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duration: secs(1.0),
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deltas: vec![("units".into(), 1000)],
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injected_cycles: 0,
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},
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// Overlapped at 50%: everyone else (incl. the real bottleneck)
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// slowed, count drops with the divisor -> ~0% impact.
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ExperimentResult {
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site: "overlapped".into(),
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speedup_pct: 50,
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duration: secs(1.0),
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deltas: vec![("units".into(), 500)],
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injected_cycles: cycles(0.5),
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},
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];
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let bn = impact_pct(&results, "bottleneck", 50, "units").unwrap();
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assert!((bn - 100.0).abs() < 5.0, "bottleneck impact: {bn}");
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let ov = impact_pct(&results, "overlapped", 50, "units").unwrap();
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assert!(ov.abs() < 5.0, "overlapped impact: {ov}");
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// Missing cells yield None, not garbage.
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assert!(impact_pct(&results, "nosuch", 50, "units").is_none());
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assert!(impact_pct(&results, "bottleneck", 50, "nosuch").is_none());
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}
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/// End-to-end controller pass over a toy workload: the report must contain a
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/// human summary naming every (site × speedup) cell and a Coz-compatible
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/// section with experiment / throughput-point lines.
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#[test]
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fn controller_produces_report() {
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smarm::init(smarm::Config::exact(2)).run(|| {
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let stop = Arc::new(AtomicBool::new(false));
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let stop2 = stop.clone();
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let worker = smarm::spawn(move || {
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while !stop2.load(Ordering::Relaxed) {
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{
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let _g = smarm::causal_site!("stage-x");
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for _ in 0..50 {
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smarm::check!();
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}
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}
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smarm::progress!("items");
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}
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});
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let results = smarm::causal::run_experiments(&smarm::causal::ExperimentPlan {
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speedups_pct: vec![0, 50],
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experiment: Duration::from_millis(60),
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cooldown: Duration::from_millis(20),
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});
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stop.store(true, Ordering::Relaxed);
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worker.join().unwrap();
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assert!(!results.is_empty());
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let summary = smarm::causal::render_summary(&results);
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assert!(summary.contains("stage-x"), "summary: {summary}");
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assert!(summary.contains("items"), "summary: {summary}");
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let coz = smarm::causal::render_coz(&results);
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assert!(coz.contains("experiment\tselected=stage-x"), "coz: {coz}");
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assert!(coz.contains("throughput-point\tname=items"), "coz: {coz}");
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});
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}
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/// A target-site entry that never hits a cold causal check must still be
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/// attributed: the guard boundaries flush the pending interval on exit and
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/// re-arm the clock on entry. Without the exit flush, in-site time between
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/// the last check and guard drop is silently discarded — measured live at
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/// ~6-7% of all target time (eff 0.93), under-reporting every impact
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/// (+83.5% where theory says +100%).
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#[test]
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fn site_boundaries_flush_tail() {
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fn tsc() -> u64 {
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// SAFETY: rdtsc has no preconditions on x86_64.
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unsafe { core::arch::x86_64::_rdtsc() }
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}
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let injected = Arc::new(AtomicU64::new(0));
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let spent = Arc::new(AtomicU64::new(0));
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let inj_out = injected.clone();
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let spent_out = spent.clone();
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smarm::init(smarm::Config::exact(1)).run(move || {
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// Experiment is live before the actor ever enters the site.
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smarm::causal::begin_experiment_for_test("tail-site", 50);
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let base = smarm::causal::global_delay_cycles();
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let a = smarm::spawn(move || {
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let t0 = tsc();
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{
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let _g = smarm::causal_site!("tail-site");
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// Burn ~20M cycles with no allocations and no `check!()`:
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// the amortised cold check can never fire, so only the
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// guard-boundary flush can attribute this time.
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let start = tsc();
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while tsc().wrapping_sub(start) < 20_000_000 {
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core::hint::spin_loop();
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}
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}
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spent_out.store(tsc().wrapping_sub(t0), Ordering::Relaxed);
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});
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a.join().unwrap();
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smarm::causal::end_experiment_for_test();
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inj_out.store(
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smarm::causal::global_delay_cycles() - base,
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Ordering::Relaxed,
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);
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});
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let injected = injected.load(Ordering::Relaxed);
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let spent = spent.load(Ordering::Relaxed);
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// At 50% the flush should attribute ≈ half the in-guard time; allow a
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// generous band for guard overhead and clock skew.
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assert!(
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injected >= spent * 40 / 100 && injected <= spent * 60 / 100,
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"boundary flush attributed {injected} of {spent} spent cycles (want ~50%)"
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);
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}
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