benches: expose preemption knobs + sweep runner
Config API changes (src/preempt.rs, src/runtime.rs):
- preempt: promote ALLOC_INTERVAL and TIMESLICE_CYCLES from bare consts to
DEFAULT_ALLOC_INTERVAL / DEFAULT_TIMESLICE_CYCLES; store active values in
thread-locals set on each actor resume so multiple runtimes can use
different settings concurrently.
- runtime: add alloc_interval / timeslice_cycles fields to Config; add
Config::alloc_interval(n) and Config::timeslice_cycles(c) builder methods;
thread the values through RuntimeInner to the reset_timeslice() call in
schedule_loop.
Bench changes:
- Add bench_cfg(threads) helper to general/tokio_favored/smarm_favored that
wraps Config::exact and reads SMARM_ALLOC_INTERVAL / SMARM_TIMESLICE_CYCLES
env vars, so the sweep script can vary knobs without recompiling.
Sweep tooling (benches/sweep.py):
- 'run': run the 3-file bench suite once; --save-baseline persists JSON
- 'regress': compare current run against baseline.json, exit 1 on any bench
that regresses >10% vs stored medians
- 'sweep': run the full SWEEP_GRID (10 points), print comparison table,
optional --save-csv; binaries pre-built so no recompile per point
Sweep results (10-point grid, 1-CPU sandbox):
- The preemption knobs have very little effect on this single-CPU machine.
Most benches move <5% across the entire grid.
- Longer timeslices (tc=600k, tc=1200k) reliably hurt spawn_storm_busy
(+11-15%) and catch_unwind_panics (+10-12%) because actors hold the
scheduler mutex longer per timeslice, stalling the storm of joinable tasks.
- Shorter timeslices (tc=150k) give a small improvement on many_timers
(-3-4%) and a wash everywhere else.
- yield_in_hot_loop and uncontended_channel are essentially flat across all
knobs — both are scheduling-dominated and call yield_now explicitly, so
the RDTSC-driven preemption path is irrelevant.
- Conclusion: the knobs matter primarily under contention (multi-core).
Re-run sweep on a multi-core machine before drawing tuning conclusions.
This commit is contained in:
Bench
126
benches/baseline-output/sweep/ai128_tc600k.txt
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126
benches/baseline-output/sweep/ai128_tc600k.txt
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smarm general benchmarks
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available parallelism: 1 threads
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ITERS=15 (+1 warmup, discarded)
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CHAIN_DEPTH=1000, YIELD_TASKS=200×1000, PRIME_N=400000/64 workers, PP_ROUNDS=1000
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================================================================================
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chained_spawn: depth 1000
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 1000 | 8721 | 8398 | 8994
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smarm 1-thread | 1000 | 8587 | 8440 | 8810
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tokio current_thread | 1000 | 124 | 124 | 294
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tokio multi-thread | 1000 | 188 | 184 | 299
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================================================================================
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yield_many: 200 tasks × 1000 yields
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 200000 | 42588 | 42084 | 45080
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smarm 1-thread | 200000 | 42252 | 41963 | 43615
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tokio current_thread | 200000 | 15101 | 14994 | 15573
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tokio multi-thread | 200000 | 15979 | 15890 | 16356
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================================================================================
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fan_out_compute: primes in [2, 400000) across 64
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 33860 | 29686 | 29491 | 31263
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smarm 1-thread | 33860 | 29841 | 29586 | 30570
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tokio current_thread | 33860 | 28652 | 28510 | 30359
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tokio multi-thread | 33860 | 34677 | 34461 | 35318
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================================================================================
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ping_pong_oneshot: 1000 rounds
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 1000 | 16909 | 16579 | 20782
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smarm 1-thread | 1000 | 16888 | 16537 | 20808
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tokio current_thread | 1000 | 925 | 911 | 1021
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tokio multi-thread | 1000 | 4192 | 4079 | 4531
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smarm tokio-favored benchmarks
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available parallelism: 1 threads
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ITERS=15 (+1 warmup, discarded)
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STORM_BACKGROUND=8, STORM_SPAWN=10000, MPSC=32×10000, TIMER_ACTORS=10000 (1–10 ms), SCALING_N=400000/64
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================================================================================
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spawn_storm_busy: 8 bg yielders + 10000 zero-work spawns
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 10000 | 145813 | 142042 | 152501
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smarm 1-thread | 10000 | 145119 | 141282 | 161294
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tokio current_thread | 10000 | 2968 | 2899 | 3231
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tokio multi-thread | 10000 | 6288 | 4289 | 12226
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================================================================================
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mpsc_contention: 32 producers × 10000 msgs → 1 consumer
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 320000 | 9662 | 9254 | 11370
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smarm 1-thread | 320000 | 9673 | 9331 | 9989
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tokio current_thread | 320000 | 18015 | 17334 | 21096
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tokio multi-thread | 320000 | 18384 | 17837 | 19534
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================================================================================
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many_timers: 10000 actors sleeping 1–10 ms
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 10000 | 160492 | 154795 | 180307
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smarm 1-thread | 10000 | 161716 | 156498 | 191986
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tokio current_thread | 10000 | 13895 | 13576 | 14913
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tokio multi-thread | 10000 | 15074 | 14665 | 16070
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================================================================================
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multi_thread_scaling: primes in [2, 400000) across 64 workers
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 33860 | 30001 | 29600 | 38039
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tokio multi 1-thread | 33860 | 29419 | 28906 | 30079
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smarm smarm-favored benchmarks
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available parallelism: 1 threads
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ITERS=15 (+1 warmup, discarded)
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RECURSE_DEPTH=500, HOT_YIELDS=500000×2, UNCONT_MSGS=1000000, PANIC_TASKS=10000
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================================================================================
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deep_recursion: depth 500
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 1 | 91 | 79 | 186
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smarm 1-thread | 1 | 87 | 81 | 131
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tokio current_thread | 1 | 25 | 25 | 103
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tokio multi-thread | 1 | 56 | 47 | 64
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================================================================================
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yield_in_hot_loop: 2 actors × 500000 yields (single thread)
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 1000000 | 190023 | 188250 | 193824
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tokio current_thread | 1000000 | 154681 | 152074 | 187328
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================================================================================
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uncontended_channel: 1→1, 1000000 msgs (single thread)
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 1000000 | 27264 | 26772 | 29512
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tokio current_thread | 1000000 | 53324 | 51744 | 59282
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================================================================================
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catch_unwind_panics: 10000 tasks, 50% panic
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================================================================================
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runtime | result | median µs | min µs | max µs
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--------------------------------------------------------------------------------
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smarm 1-thread | 10000 | 155983 | 152595 | 161438
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smarm 1-thread | 10000 | 162122 | 156170 | 200357
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tokio current_thread | 10000 | 276303 | 264291 | 296266
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tokio multi-thread | 10000 | 271350 | 267654 | 285897
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