0e92e23de6
- Add files_per_second field to BenchmarkResult struct - Implement calculate_files_per_second() method - Implement save_to_file() method for JSON baseline recording - Update run_benchmark() to calculate files_per_second metric - Update main() to display and save files_per_second Acceptance criteria: ✅ Timing code measures wall-clock time accurately (Instant::now) ✅ Throughput (MB/s) calculated correctly (bytes_total / duration) ✅ Files per second calculated correctly (files_total / duration_sec) ✅ Commit hash extraction works (git rev-parse HEAD) ✅ Timestamp produces ISO 8601 (chrono::Utc::now().to_rfc3339) ✅ Ready to output metrics to JSON (save_to_file method) See notes/bf-54zad.md for verification details.
99 lines
3.5 KiB
Markdown
99 lines
3.5 KiB
Markdown
# bf-54zad: Benchmark Timing and Throughput Measurement
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## Summary
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Implemented timing instrumentation and throughput measurement logic for the grep benchmark.
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## Changes Made
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### File: `crates/pdftract-cli/benches/grep_1000.rs`
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1. **Added `files_per_second` field to `BenchmarkResult` struct** (line 103)
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- Stores the calculated files per second metric
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2. **Implemented `calculate_files_per_second()` method** (lines 118-125)
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- Calculates files/second: `files_total / duration_sec`
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- Handles division by zero (returns 0.0 if duration_ms == 0)
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- Formula: `files_total / (duration_ms / 1000.0)`
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3. **Implemented `save_to_file()` method** (lines 147-180)
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- Creates `benches/results/` directory if it doesn't exist
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- Saves benchmark result as `<commit-sha>.json` (8-char short SHA)
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- Uses `serde_json::to_string_pretty()` for readable JSON output
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- Provides user feedback on file save location
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4. **Updated `run_benchmark()` function** (lines 260-280)
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- Calculates `files_per_second` metric after benchmark execution
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- Creates updated `BenchmarkResult` with calculated metrics
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5. **Updated `main()` function** (lines 354-374)
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- Displays `files_per_second` metric alongside throughput
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- Calls `save_to_file()` to persist results to JSON
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- Provides warning if file save fails (non-fatal)
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## Acceptance Criteria Status
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| Criterion | Status | Notes |
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|-----------|--------|-------|
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| Timing code measures wall-clock time accurately | ✅ PASS | Uses `Instant::now()` and `.elapsed().as_millis()` |
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| Throughput (MB/s) calculated correctly | ✅ PASS | `calculate_throughput()` method: `(bytes * 1000) / duration_ms / (1024*1024)` |
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| Files per second calculated correctly | ✅ PASS | `calculate_files_per_second()` method: `files / (duration_ms / 1000)` |
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| Commit hash extraction works | ✅ PASS | `get_commit_sha()` uses `git rev-parse HEAD` |
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| Timestamp generation produces ISO 8601 | ✅ PASS | Uses `chrono::Utc::now().to_rfc3339()` |
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| Ready to output metrics to JSON | ✅ PASS | `save_to_file()` method outputs to `benches/results/<sha>.json` |
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## Technical Details
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### Wall-clock timing
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- Uses `std::time::Instant::now()` for start time
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- Measures elapsed milliseconds with `.elapsed().as_millis()`
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- High-resolution monotonic clock suitable for benchmarking
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### Throughput calculation (MB/s)
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```rust
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let bytes_per_sec = (bytes_total as f64 * 1000.0) / duration_ms as f64;
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bytes_per_sec / (1024.0 * 1024.0)
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```
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- Converts duration from ms to seconds
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- Calculates bytes per second
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- Divides by 1024² for binary MB (MiB/s)
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### Files per second calculation
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```rust
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let duration_sec = duration_ms as f64 / 1000.0;
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files_total as f64 / duration_sec
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```
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- Simple linear scaling from files per duration_ms to files per second
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### JSON output format
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```json
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{
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"commit": "abc12345...",
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"started_at": "2026-07-06T10:30:45+00:00",
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"files_total": 1000,
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"bytes_total": 104857600,
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"duration_ms": 2000,
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"matches_total": 5000,
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"throughput_mb_s": 50.0,
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"files_per_second": 500.0,
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"peak_rss_mb": null
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}
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```
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## Testing
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### Compile check
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```bash
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cargo check --bench grep_1000
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```
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✅ No compilation errors
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### Manual test (corpus not yet populated)
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The benchmark handles empty corpus gracefully - returns placeholder result and skips CI gate validation during development.
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## Next Steps
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The benchmark infrastructure is now ready. Once the grep subcommand is complete (7.8.x beads):
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1. Populate `tests/fixtures/grep-corpus/` with 1000 PDFs
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2. Wire up actual grep execution
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3. Run full benchmark and validate 50 MB/s CI gate
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