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Adds four Criterion.rs benchmark suites to measure hot-path performance
and demonstrate the impact of Sprints 1–3 optimizations:
- benches/protocol.rs — Command & StatusMessage serialize/deserialize
- benches/bandwidth.rs — BandwidthState atomics, budget, interval math
- benches/tcp_rx_scan.rs — memchr SIMD scan vs naive O(n) loop (55× faster
on 256KB buffers with status at end)
- benches/ecsrp5.rs — WCurve::new() heavy math vs cached LazyLock
(~123,000× faster access)
Also adds BENCHMARKS.md with usage instructions and example results.
Visibility changes (bench-only):
- scan_status_message is now pub (was #[cfg(test)] only)
- WCurve and WCURVE are now pub in ecsrp5.rs
dev-dependencies: criterion + pprof (optional flamegraph support)
55 lines
1.9 KiB
Markdown
55 lines
1.9 KiB
Markdown
# Benchmarks
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This project uses [Criterion.rs](https://bheisler.github.io/criterion.rs/book/) for performance benchmarking and regression detection.
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## Running Benchmarks
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Run all benchmarks:
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```bash
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cargo bench
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```
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Run a specific benchmark suite:
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```bash
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cargo bench --bench protocol
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cargo bench --bench bandwidth
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cargo bench --bench tcp_rx_scan
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cargo bench --bench ecsrp5
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```
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Run in "quick" mode (fewer iterations, useful for development):
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```bash
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cargo bench --bench tcp_rx_scan -- --quick
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```
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## Benchmark Suites
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### `protocol` — Protocol Serialization
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Measures the zero-allocation serialization/deserialization of `Command` (16 bytes) and `StatusMessage` (12 bytes) structs.
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### `bandwidth` — Bandwidth State Atomics
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Measures `BandwidthState` hot-path operations: `fetch_add`, `spend_budget`, `calc_send_interval`, `advance_next_send`, and `summary`.
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### `tcp_rx_scan` — TCP RX Status Message Scan
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Compares the optimized `memchr`-based scan against the old naive O(n) byte-by-byte loop on 256KB buffers. Key scenarios:
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- **All zeros** (common case — data packets contain no status)
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- **Status at start**
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- **Status at end** (worst case for naive scan)
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- **Split messages** (status spans two TCP reads)
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### `ecsrp5` — EC-SRP5 Curve Construction
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Compares `WCurve::new()` (heavy `BigUint` modular arithmetic) against the cached `&*WCURVE` access to demonstrate the Sprint 1 optimization.
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## Interpreting Results
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Criterion generates HTML reports in `target/criterion/`. Open `target/criterion/report/index.html` after running benchmarks to view interactive charts.
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Example results (Apple M3 Pro, release profile):
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| Benchmark | Naive/Uncached | Optimized/Cached | Speedup |
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|-----------|---------------|------------------|---------|
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| TCP RX scan 256KB (status at end) | 251 µs | 4.5 µs | **~55×** |
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| WCurve construction | 126 µs | 1.0 ns | **~123,000×** |
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| Command serialize | — | 7.7 ns | — |
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| Bandwidth `fetch_add` | — | ~1 ns | — |
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