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/ai64_tc150k.txt
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126
benches/baseline-output/sweep/ai64_tc150k.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 | 8849 | 8486 | 9224
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smarm 1-thread | 1000 | 8841 | 8477 | 9108
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tokio current_thread | 1000 | 124 | 124 | 219
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tokio multi-thread | 1000 | 187 | 184 | 283
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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 | 41681 | 41278 | 43685
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smarm 1-thread | 200000 | 41721 | 41218 | 42261
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tokio current_thread | 200000 | 14969 | 14940 | 15051
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tokio multi-thread | 200000 | 16004 | 15868 | 17569
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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 | 29679 | 29516 | 30105
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smarm 1-thread | 33860 | 29677 | 29594 | 31365
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tokio current_thread | 33860 | 28656 | 28572 | 29239
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tokio multi-thread | 33860 | 34783 | 34617 | 36531
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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 | 17009 | 16822 | 17418
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smarm 1-thread | 1000 | 16866 | 16723 | 17315
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tokio current_thread | 1000 | 880 | 871 | 1035
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tokio multi-thread | 1000 | 4263 | 4178 | 4391
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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 | 126566 | 124995 | 130402
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smarm 1-thread | 10000 | 128278 | 126209 | 135156
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tokio current_thread | 10000 | 2680 | 2640 | 2787
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tokio multi-thread | 10000 | 7411 | 4393 | 12421
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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 | 9073 | 8937 | 9324
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smarm 1-thread | 320000 | 9120 | 9018 | 9263
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tokio current_thread | 320000 | 17245 | 17180 | 17574
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tokio multi-thread | 320000 | 18518 | 17685 | 19621
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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 | 141855 | 135415 | 145810
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smarm 1-thread | 10000 | 138265 | 135535 | 142346
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tokio current_thread | 10000 | 14441 | 13453 | 14650
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tokio multi-thread | 10000 | 14956 | 14529 | 15451
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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 | 30033 | 29659 | 31803
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tokio multi 1-thread | 33860 | 29078 | 28963 | 30231
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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 | 83 | 79 | 132
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smarm 1-thread | 1 | 85 | 78 | 146
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tokio current_thread | 1 | 25 | 25 | 73
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tokio multi-thread | 1 | 51 | 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 | 191352 | 188830 | 196235
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tokio current_thread | 1000000 | 152382 | 150674 | 187815
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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 | 27552 | 27099 | 30612
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tokio current_thread | 1000000 | 53160 | 52436 | 55255
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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 | 145243 | 143291 | 173727
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smarm 1-thread | 10000 | 145242 | 142819 | 148457
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tokio current_thread | 10000 | 266471 | 262904 | 269145
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tokio multi-thread | 10000 | 274195 | 269312 | 286111
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