- causal_pipeline: SMARM_CAUSAL_AUDIT=1 appends render_ledger_audit()
after the summary; pinned summary format untouched.
- causal_attrib_probe: per-pct audit line (absorbed/forgiven/drops/
discards) under the existing eff line, so in-site-vs-attributed and
the loss buckets land in one place for the sweep.
1-core smoke (work + wide): books balance — absorbed = 2x injected and
forgiven = 2x injected, i.e. owed = injected x (N-1) with N=5 actors,
zero outstanding. drop park = 0 even in wide mode (the bottleneck's
queue is never empty, so its in-guard recv never parks); drop yield is
~1500 events but ~0.1ms per window, confirming slice-expiry yields
sample at their own checkpoint. Deficit decomposition needs the
parallel box.
Measure-only counters for the deficit hunt (~23ms short per 700ms window
at 50% on the bottleneck site; superlinear vs 25%). Nothing here changes
injection or absorption; the sweep decides the fix.
Buckets, windowed per cell into new ExperimentResult fields (audit
snapshot taken at end() — spin/attribution freeze there, forgiveness
does not):
- spin_absorbed / park_forgiven: where owed delay actually went. Spin
during a 0% cell is the baseline-contamination signature — leftover
debt from a prior window being paid in a later one (checks gate on
the experiment word, so cooldowns pay nothing and debt carries over).
- drop_park / drop_yield (+counts): the deschedule path flushes no
sample tail — an in-target-site park or yield silently loses
[last sample -> now]; on_resume re-arms before the actor runs again.
New on_deschedule hook in all three intent arms (real park; explicit/
slice-expiry yield; requeued park counts as yield — it never blocked).
Slice-expiry yields sample at the descheduling checkpoint, so a fat
yield bucket points at explicit yield_now or requeued parks.
- discard_overmax (+count, in would-be delta terms so columns compare
against injected_cycles) / discard_unarmed: the attribute() clamps,
previously silent.
LedgerCounters + ledger_counters() expose cumulative totals (tests,
run-level prints); render_ledger_audit() is the per-cell companion to
render_summary, which stays byte-identical (pinned). ExperimentResult
now derives Default so literals survive future audit-field growth.
Tests: +7 (spin counted, forgiveness counted, in-site park drop, in-site
yield drop, overmax discard, 0%-window leftover absorption — synthesized
deterministically via inject_delay_cycles_for_test with no experiment
active — and the audit render). 22/22 causal.
One unconditional footer line whenever there are results:
"note: impacts are lower bounds — undershoot grows with speedup pct;
rankings unaffected" — surfacing the RFC 007 Validation fidelity statement
where users actually look, instead of only in the RFC. Wording pinned by
the summary test.
send_after_wall / send_after_named_wall (+ Timers::insert_send_wall) arm a
message-delivery timer that opts out of the RFC 007 virtual-time shift and
fires at its raw deadline regardless of injected delay — the Send-reason
sibling of sleep_wall, closing the jar item whose substrate efbc254 landed.
For deadlines that reflect the outside world (protocol timeouts, wall-clock
schedules) rather than workload pacing. cancel_timer is anchor-agnostic and
unchanged; without the feature the API exists and is identical to send_after.
The gen_server timer layer (send_after_to, RFC 015 §5) deliberately stays
virtual-only — an opt-out there means new options on the gen_server/statem
timeout API, out of scope for now.
Tests: wall send fires at raw deadline while a virtual sibling shifts;
cancel on a wall send with debt outstanding; featureless delivery/cancel
smokes through the public named API. 15/15 causal, 34/34 binaries both
feature configs, lib clippy clean both.
Occupancy probe on 24 cores: δ = 0.3µs/item (0.1% of the serialized
path); wide guard leaves the @50% cell unchanged. The +84-vs-+100
shortfall is controller-side (injected 327ms of the ideal 350ms over
the 700ms window, plus ~3% real-rate dip during experiments), not
unguarded stage time. urus's ~70µs/request remainder remains the
guard-placement case; the occupancy probe discriminates the two.
SMARM_CAUSAL_MODE selects the reserve stage's guard placement:
work (default, unchanged) | wide (guard over recv+work+send, the whole
serialized per-item path) | occupancy (no experiments; per-segment
timing of reserve's loop at baseline, reporting the unguarded
remainder δ and the impact ceiling it implies).
Discriminates the two candidate explanations for the demo's +84-vs-+100
@50% shortfall: physical recv/send time outside the guard (occupancy
sees δ≈30µs, wide recovers ~2x) vs. injection-side credit loss
(occupancy sees δ≈0, wide caps at ~+84 too — guard cadence identical).
New timer anchor: insert_sleep_wall / scheduler::sleep_wall (exported) opt a
Sleep entry out of the RFC 007 virtual-time shift, so it fires at its raw
deadline regardless of injected delay. Featureless config is unchanged (the
API exists but is identical to sleep).
The causal controller's window/cooldown sleeps and the tsc_hz calibration
sleep use it on the actor path (the OS-thread path was already wall). This
fixes the controller's own sleeps dilating under its own injection —
experiment windows stretched ~2x at 50% speedup (337ms -> 646ms injected/
window). Deltas were rate-normalized so results were unbiased; this fixes
sweep cost, not bias. The general wall-anchored-timer-semantics jar item
(user-facing opt-out) remains open; this lands the substrate.
Test: wall_timer_ignores_injected_delay — wall entry fires at raw deadline
while a virtual sibling in the same heap shifts. 13/13 causal, 34/34
binaries both feature configs.
Injected delays dilate virtual time for the workload, but timer deadlines
stayed wall-anchored: a sleep or receive-timeout fired early in virtual
terms, so timeout/retry behaviour sped up relative to the dilated world
(v1 known gap #1).
Every heap Entry now carries delay_stamp — the global delay ledger at
(re-)queue time, cfg-gated on smarm-causal. pop_due converts any debt
accrued since the stamp to wall time (tsc_hz) and shifts the effective
deadline; a not-yet-due entry is re-queued at the shifted deadline with a
fresh stamp, so it keeps chasing delay injected while it waits. seq is
preserved across re-queues, keeping send_after cancellation identity
intact (cancelled entries are discarded before any shift). Zero debt is
byte-identical to the old path; peek_deadline may under-report, costing
one spurious scheduler wake per injected chunk (documented).
This also makes the park-gated resume credit *correct* rather than
forgiving for sleepers: a sleeping actor now physically pays its debt by
sleeping longer, so the on_resume fast-forward reflects real payment
(sleeping_actor_pays_injected_delay pins this end-to-end through the
runtime).
New test hooks: inject_delay_cycles_for_test (deterministic ledger
driver, eagerly TSC-calibrating so conversion never stalls a scheduler
loop) and cycles_to_duration. The ledger is process-global, so the
delta-sensitive causal tests now serialize on a shared test mutex — they
were racy under the parallel test harness before this, in principle.
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.
causal_site! scoped site guards per actor slot, progress! throughput
points, and a Coz-style virtual-speedup engine hooked into
maybe_preempt's amortized cold block: target-site samples grow a global
delay ledger; bystanders spin-absorb their debt at the next causal
check, with timeslice extension so injected delay is not charged
against the slice.
Resume credit (Coz's blocked-thread rule) is gated on a causal_parked
slot bit set only by a real park: crediting on every resume made any
yield-cadence actor delay-immune and every experiment inert (found
live on a 24-core run — dead-flat deltas across all sites).
Report normalization uses a measured TSC frequency (~50ms calibration
on first use) instead of the crate-wide 3 GHz assumption, which
uniformly inflated impact numbers on a 3.7 GHz box. impact_pct() is
the machine-readable form of the summary for programmatic checks.
examples/causal_pipeline.rs burns fixed *work* (calibrated LCG loop),
not fixed wall time — a timed busy-wait absorbs injected delay into
its own budget and reads as a no-op. Self-checking: exits nonzero if
causal separation fails; skips the verdict below 4 cores. Validated
on a 24-core box: reserve (true bottleneck) +29.3%@25/+83.5%@50;
serialize and background-compaction ~0%.
Known v1 gaps (jar): timer-heap deadlines unshifted, no-check!/no-alloc
actors undelayable, multi-scheduler coherence best-effort Relaxed,
off-CPU blame punted, Instant::now() uncorrected.
Zero-cost with the feature off; clippy -D warnings clean both ways;
full suite green with and without smarm-causal.
Claude (sandbox)