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//! End-to-end coverage for the [`PhaseMapExt`] cross-phase
//! comparator + [`pickers::max_by_counter_value`] picker that
//! shrink the swap-counter-A/B-test pattern down to a 6-line
//! post_vm callback.
//!
//! Boots a single 2-Step scenario with periodic captures across
//! both Steps so the resulting [`SampleSeries`] carries Step[0]
//! and Step[1] samples. The post_vm callback exercises the full
//! pipeline the way a real A/B test does:
//!
//! 1. Project a cumulative BPF counter via
//! `series.bpf("...", |snap| snap.var("...").as_u64())`.
//! 2. Reduce per phase via
//! [`SeriesField::counter_delta_per_phase`].
//! 3. Compose with another projection via
//! [`PhaseMapExt::zip_per_phase`].
//! 4. Compare across phases via
//! [`PhaseMapExt::ratio_across_phases`]`.at_most(...)`.
//! 5. Confirm the verdict carries either an info note (pass arm)
//! or a failure detail mentioning the comparator (fail arm).
//!
//! The test does NOT pin which arm fires because scheduler
//! activity across the window depends on host load — but it
//! pins the comparator chain produces a recorded verdict
//! mutation either way, end-to-end through the real VM.
use anyhow::Result;
use ktstr::assert::{AssertResult, Phase, PhaseMapExt, Verdict};
use ktstr::ktstr_test;
use ktstr::prelude::VmResult;
use ktstr::scenario::Ctx;
use ktstr::scenario::ops::{CgroupDef, HoldSpec, Step, execute_steps};
use ktstr::test_support::{Scheduler, SchedulerSpec};
const KTSTR_SCHED: Scheduler =
Scheduler::named("ktstr_sched").binary(SchedulerSpec::Discover("scx-ktstr"));
/// Generous ceiling for the cross-phase ratio. scx-ktstr's
/// dispatch counter grows monotonically across the window so the
/// step(0)→step(1) ratio is unbounded above; a ceiling of 10⁹
/// keeps the comparator on the pass arm regardless of host load
/// while still exercising the pass-arm info-note path.
const RATIO_CEILING: f64 = 1_000_000_000.0;
fn assert_phase_map_ext_pipeline(result: &VmResult) -> Result<()> {
let periodic_fired = result.periodic_fired;
let periodic_target = result.periodic_target;
anyhow::ensure!(
periodic_fired >= 2,
"periodic_fired = {periodic_fired} of {periodic_target} — \
counter_delta_per_phase needs at least 2 Ok samples per phase \
to produce a non-zero delta",
);
let series = result.periodic_series();
// counter_delta_per_phase requires the SeriesField projection to
// be sample-axis stamped with per-phase tags (which periodic_series
// does via the build_series_field phase-threading path). Project
// the framework's BPF dispatch counter once per "sub-projection"
// so we exercise zip_per_phase on real data: same / cross-axes of
// dispatch.
//
// scx-ktstr doesn't actually carry per-LLC same/cross axes (it's
// a single-bss counter), so we synthesize an A/B shape by reading
// the same counter twice and zipping with itself. The result is
// identical per-phase delta values; the test's load-bearing
// claim is that the chain composes + records a verdict, NOT
// that the metric value is meaningful here.
let a_delta = series
.bpf("nr_dispatched_a", |snap| {
snap.var("nr_dispatched").as_u64().map(|v| v as f64)
})
.counter_delta_per_phase();
let b_delta = series
.bpf("nr_dispatched_b", |snap| {
snap.var("nr_dispatched").as_u64().map(|v| v as f64)
})
.counter_delta_per_phase();
// Step pins: at least one Step phase produced a delta on the
// self-zip. If both maps are empty, the phase-stamp pipeline
// is broken upstream — surface that loudly rather than letting
// the comparator silently no-op on an empty zip result.
anyhow::ensure!(
a_delta.contains_key(&Phase::step(0)) || a_delta.contains_key(&Phase::step(1)),
"counter_delta_per_phase produced no Step buckets despite \
periodic_fired = {periodic_fired}; either the phase pipeline \
isn't stamping samples, or every sample within both phases is \
an Err. a_delta keys = {:?}",
a_delta.keys().collect::<Vec<_>>(),
);
// zip_per_phase exercises the intersection-only fold with a
// by-value closure (Copy bound on f64) — pins the trait isn't
// forcing deref noise on the composition body.
let synthetic_frac = a_delta.zip_per_phase(&b_delta, |a, b| {
let total = a + b;
if total == 0.0 { 0.0 } else { a / total }
});
anyhow::ensure!(
!synthetic_frac.is_empty(),
"zip_per_phase yielded an empty result map despite both \
input maps having Step phases; intersection of a_delta keys = \
{:?} with b_delta keys = {:?} should not be empty",
a_delta.keys().collect::<Vec<_>>(),
b_delta.keys().collect::<Vec<_>>(),
);
// self-zip cross_frac = a / (a + a) = 0.5 for any non-zero phase.
for (phase, value) in &synthetic_frac {
if *value > 0.0 {
anyhow::ensure!(
(value - 0.5).abs() < 1e-9,
"self-zip cross_frac for {phase:?} = {value}, expected 0.5",
);
}
}
// PhaseMap::ratio_across_phases lands the verdict. If only one
// Step phase was populated by counter_delta_per_phase, the
// "needs both phases" arm fires — that's still a recorded
// verdict mutation. Pin EITHER the pass-arm info note OR the
// missing-phase fail detail (both prove the comparator ran).
let mut verdict = Verdict::new();
synthetic_frac
.ratio_across_phases(
&mut verdict,
"synthetic_frac",
Phase::step(0),
Phase::step(1),
)
.at_most(RATIO_CEILING);
let r = verdict.into_result();
let recorded_pass = r
.info_notes
.iter()
.any(|n| n.message.contains("synthetic_frac"));
let recorded_fail = r
.failure_details()
.any(|d| d.message.contains("synthetic_frac"));
anyhow::ensure!(
recorded_pass || recorded_fail,
"PhaseMapExt::ratio_across_phases produced NEITHER a pass info \
note NOR a failure detail mentioning the supplied label — \
the chain didn't fire. info_notes = {:?}, details = {:?}",
r.info_notes,
r.failure_details().collect::<Vec<_>>(),
);
Ok(())
}
/// 2-Step scenario with periodic captures across both Steps —
/// mirrors `phase_pipeline_two_step_e2e` so the CURRENT_STEP atomic
/// advances at the boundary and periodic samples land in both
/// `Phase::step(0)` and `Phase::step(1)` buckets that
/// `counter_delta_per_phase` reduces over.
#[ktstr_test(
scheduler = KTSTR_SCHED,
llcs = 1,
cores = 2,
threads = 1,
duration_s = 10,
watchdog_timeout_s = 20,
num_snapshots = 6,
auto_repro = false,
post_vm = assert_phase_map_ext_pipeline,
)]
fn phase_map_ext_compose_zip_then_ratio_across_phases_e2e(ctx: &Ctx) -> Result<AssertResult> {
let steps = vec![
Step {
setup: vec![CgroupDef::named("cg_step0").workers(2)].into(),
ops: vec![],
hold: HoldSpec::frac(0.5),
},
Step {
setup: vec![CgroupDef::named("cg_step1").workers(2)].into(),
ops: vec![],
hold: HoldSpec::frac(0.5),
},
];
execute_steps(ctx, steps)
}