hotpath 0.30.2

One profiler for CPU, time, memory, SQL, and async code - quickly find and debug performance bottlenecks.
Documentation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
#[path = "common/support.rs"]
mod common;

#[cfg(all(test, feature = "hotpath"))]
pub mod tests {
    use std::process::Output;

    use hotpath::json::{JsonFunctionsList, JsonReport};

    use crate::common::callgrind::{valgrind_available, RunDir};
    use crate::common::example::{assert_success, Example};
    use crate::common::report::parse_report;

    const ITERATIONS: u64 = 1000;
    const ROUTINE: &str = "hotpath::criterion::routine";
    const ASYNC_ROUTINE: &str = "hotpath::criterion::async_routine";
    const BENCH: &str = "hotpath::criterion::bench";
    const WORK: &str = "fixture::work";

    #[derive(Debug, PartialEq)]
    struct Counts {
        routine_calls: u64,
        setup_calls: u64,
        input_drops: u64,
        output_drops: u64,
    }

    #[track_caller]
    fn counts(output: &Output) -> Counts {
        let stderr = String::from_utf8_lossy(&output.stderr);
        let line = stderr
            .lines()
            .rev()
            .find_map(|l| l.strip_prefix("fixture: "))
            .unwrap_or_else(|| panic!("no fixture counts in stderr:\n{stderr}"));
        let field = |name: &str| -> u64 {
            line.split(' ')
                .find_map(|kv| kv.strip_prefix(name)?.strip_prefix('='))
                .and_then(|v| v.parse().ok())
                .unwrap_or_else(|| panic!("no {name} in {line:?}"))
        };
        Counts {
            routine_calls: field("routine_calls"),
            setup_calls: field("setup_calls"),
            input_drops: field("input_drops"),
            output_drops: field("output_drops"),
        }
    }

    fn fixture(features: &str) -> Example {
        Example::new("test-criterion", "fixture")
            .features(features)
            .env_remove("HOTPATH_CRITERION_ITERATIONS")
    }

    fn fixed(features: &str, benchmark: &str) -> Example {
        fixture(features)
            .env("HOTPATH_CRITERION_ITERATIONS", ITERATIONS.to_string())
            .env("HOTPATH_FUNCTIONS_LIMIT", "0")
            .args(&["--exact", benchmark])
    }

    #[track_caller]
    fn entry<'a>(list: &'a JsonFunctionsList, name: &str) -> &'a hotpath::json::JsonFunctionEntry {
        list.data
            .iter()
            .find(|e| e.name == name)
            .unwrap_or_else(|| panic!("{name} missing from {:#?}", list.data))
    }

    /// The per-iteration row of `benchmark`.
    fn routine_row(benchmark: &str) -> &'static str {
        if benchmark.starts_with("async/") {
            ASYNC_ROUTINE
        } else {
            ROUTINE
        }
    }

    #[track_caller]
    fn bytes(value: &str) -> u64 {
        hotpath::parse_bytes(value).unwrap_or_else(|| panic!("not bytes: {value:?}"))
    }

    /// `hotpath-cloud` renders JSON values at exact precision.
    #[track_caller]
    fn fixed_run(benchmark: &str) -> (Counts, JsonReport) {
        let output = fixed("hotpath,hotpath-alloc,hotpath-cloud", benchmark)
            .json()
            .env_remove("HOTPATH_UPLOAD")
            .env_remove("GITHUB_ACTIONS")
            .env("HOTPATH_REPORT", "functions-timing,functions-alloc")
            .output();
        assert_success(&output);
        (
            counts(&output),
            parse_report(&String::from_utf8_lossy(&output.stdout)),
        )
    }

    // HOTPATH_CRITERION_ITERATIONS=1000 cargo run -p test-criterion --example fixture --features hotpath,hotpath-alloc -- --exact work/iter_batched_per_iteration
    // HOTPATH_CRITERION_ITERATIONS=1000 cargo run -p test-criterion --example fixture --features hotpath,hotpath-alloc -- --exact async/iter_multi_thread
    #[test]
    fn test_fixed_iterations_run_each_routine_exactly_n_times() {
        let n = ITERATIONS;
        // (benchmark, setups, routine bytes per call, bench row bytes per
        // iteration, whether the bench row holds exactly those). The `async/`
        // routines yield before calling `run`, so their bytes are allocated
        // after an `.await`.
        let cases = [
            ("top_level", 0, 64 + 32, 0, true),
            ("top_input/9", 0, 64 + 32, 0, true),
            ("work/iter", 0, 64 + 32, 0, true),
            ("inputs/work/3", 0, 64 + 32, 0, true),
            ("inputs/seven", 0, 64 + 32, 0, true),
            (
                "work/iter_batched_per_iteration",
                n,
                64 + 16,
                1024 + 32,
                true,
            ),
            ("work/iter_batched", n, 64 + 16, 1024 + 32, false),
            (
                "work/iter_batched_ref_per_iteration",
                n,
                64,
                1024 + 32 + 16,
                true,
            ),
            ("work/iter_batched_ref", n, 64, 1024 + 32 + 16, true),
            ("async/iter", 0, 64 + 32, 0, true),
            ("async/iter_multi_thread", 0, 64 + 32, 0, true),
            (
                "async/iter_batched_per_iteration",
                n,
                64 + 16,
                1024 + 32,
                true,
            ),
            ("async/iter_batched", n, 64 + 16, 1024 + 32, false),
            (
                "async/iter_batched_ref_per_iteration",
                n,
                64,
                1024 + 32 + 16,
                true,
            ),
            ("async/iter_batched_ref", n, 64, 1024 + 32 + 16, true),
        ];
        for (benchmark, setups, routine_bytes, bench_bytes, exact) in cases {
            let (counts, report) = fixed_run(benchmark);
            assert_eq!(
                counts,
                Counts {
                    routine_calls: n,
                    setup_calls: setups,
                    input_drops: setups,
                    output_drops: n,
                },
                "{benchmark}"
            );
            let metadata = report.user_metadata.as_ref().expect("user metadata");
            assert_eq!(
                metadata.get("criterion_iterations").map(String::as_str),
                Some("1000")
            );
            assert_eq!(
                metadata.get("criterion_benchmark").map(String::as_str),
                Some(benchmark)
            );

            let routine = routine_row(benchmark);
            let timing = report.functions_timing.as_ref().expect("timing section");
            assert_eq!(timing.caller_name, BENCH);
            for name in [routine, WORK] {
                let e = entry(timing, name);
                assert_eq!((e.calls, e.sampled_calls), (n, n), "{benchmark} {name}");
            }
            assert_eq!(entry(timing, BENCH).calls, 1);
            let total = |name: &str| hotpath::parse_duration(&entry(timing, name).total).unwrap();
            assert!(
                total(routine) > total(WORK),
                "{benchmark}: the routine row must include the work it awaits"
            );
            for other in [ROUTINE, ASYNC_ROUTINE]
                .into_iter()
                .filter(|r| *r != routine)
            {
                assert!(timing.data.iter().all(|e| e.name != other), "{benchmark}");
            }

            let alloc = report.functions_alloc.as_ref().expect("alloc section");
            assert_eq!(bytes(&entry(alloc, WORK).avg), 512, "{benchmark}");
            assert_eq!(
                bytes(&entry(alloc, routine).avg),
                routine_bytes,
                "{benchmark}: setup and drops outside the routine must not be attributed to it"
            );
            let bench_total = bytes(&entry(alloc, BENCH).total);
            let expected = bench_bytes * n;
            if exact && routine == ASYNC_ROUTINE {
                // Plus the executor's per-`block_on` bookkeeping.
                assert!(
                    (expected..expected + 1024).contains(&bench_total),
                    "{benchmark}: bench row {bench_total} B, expected {expected} B"
                );
            } else if exact {
                assert_eq!(
                    bench_total, expected,
                    "{benchmark}: setup and drops outside the routine belong to the bench row"
                );
            } else {
                assert!(
                    bench_total > expected,
                    "{benchmark}: bench row {bench_total} B, expected over {expected} B"
                );
            }
        }
    }

    // HOTPATH_CRITERION_ITERATIONS=1000 cargo run -p test-criterion --example fixture --features hotpath,hotpath-alloc -- --exact async/iter_custom
    #[test]
    fn test_iter_custom_gets_the_iteration_count() {
        for benchmark in ["work/iter_custom", "async/iter_custom"] {
            let (counts, report) = fixed_run(benchmark);
            assert_eq!(counts.routine_calls, ITERATIONS, "{benchmark}");
            let timing = report.functions_timing.expect("timing section");
            assert_eq!(entry(&timing, WORK).calls, ITERATIONS, "{benchmark}");
            assert!(
                timing
                    .data
                    .iter()
                    .all(|e| e.name != ROUTINE && e.name != ASYNC_ROUTINE),
                "{benchmark}: iter_custom loops on its own, so it has no per-iteration row"
            );
        }
    }

    // cargo run -p test-criterion --example fixture --features hotpath -- --exact async/iter_batched
    #[test]
    fn test_without_iterations_criterion_runs_unchanged() {
        for prefix in ["work", "async"] {
            // Test mode (implied by `cargo run`): one iteration, no report.
            let output = fixture("hotpath")
                .json()
                .args(&["--exact", &format!("{prefix}/iter_batched")])
                .output();
            assert_success(&output);
            assert_eq!(
                counts(&output),
                Counts {
                    routine_calls: 1,
                    setup_calls: 1,
                    input_drops: 1,
                    output_drops: 1,
                },
                "{prefix}"
            );
            let stdout = String::from_utf8_lossy(&output.stdout);
            assert!(
                !stdout.contains('{'),
                "no hotpath report expected:\n{stdout}"
            );

            // Benchmark mode: Criterion's own warm-up and sampling loop.
            let output = fixture("hotpath")
                .json()
                .args(&[
                    "--bench",
                    "--exact",
                    &format!("{prefix}/iter"),
                    "--discard-baseline",
                ])
                .output();
            assert_success(&output);
            let stdout = String::from_utf8_lossy(&output.stdout);
            assert!(stdout.contains("time:"), "no Criterion estimate:\n{stdout}");
            assert!(
                !stdout.contains('{'),
                "no hotpath report expected:\n{stdout}"
            );
            assert!(counts(&output).routine_calls > ITERATIONS, "{prefix}");
        }
    }

    // HOTPATH_CRITERION_ITERATIONS=1000 cargo run -p test-criterion --example fixture --features hotpath -- async/iter
    #[test]
    fn test_fixed_iterations_refuse_a_second_benchmark() {
        for benchmark in ["work/iter", "async/iter"] {
            // A regex filter matching several benchmarks.
            let output = fixture("hotpath")
                .env("HOTPATH_CRITERION_ITERATIONS", "10")
                .args(&[benchmark])
                .output();
            assert!(!output.status.success(), "{benchmark}");
            let stderr = String::from_utf8_lossy(&output.stderr);
            assert!(stderr.contains("a second one started"), "{stderr}");

            // Criterion's benchmark mode enters the routine once per sample.
            let output = fixture("hotpath")
                .env("HOTPATH_CRITERION_ITERATIONS", "10")
                .args(&["--bench", "--exact", benchmark, "--discard-baseline"])
                .output();
            assert!(!output.status.success(), "{benchmark}");
            let stderr = String::from_utf8_lossy(&output.stderr);
            assert!(stderr.contains("a second one started"), "{stderr}");
        }
    }

    // HOTPATH_CRITERION_ITERATIONS=1000 cargo run -p test-criterion --example fixture --features hotpath -- --exact missing
    #[test]
    fn test_fixed_iterations_fail_when_nothing_ran() {
        let output = fixed("hotpath", "missing").output();
        assert_eq!(output.status.code(), Some(1));
        let stderr = String::from_utf8_lossy(&output.stderr);
        assert!(stderr.contains("no benchmark ran"), "{stderr}");
    }

    // HOTPATH_CRITERION_ITERATIONS=many cargo run -p test-criterion --example fixture --features hotpath -- --exact work/iter
    #[test]
    fn test_malformed_iterations_fail() {
        for value in ["many", "0", "-5"] {
            let output = fixture("hotpath")
                .env("HOTPATH_CRITERION_ITERATIONS", value)
                .args(&["--exact", "work/iter"])
                .output();
            assert!(!output.status.success(), "{value}");
            let stderr = String::from_utf8_lossy(&output.stderr);
            assert!(
                stderr.contains("HOTPATH_CRITERION_ITERATIONS: expected a positive integer"),
                "{value}: {stderr}"
            );
        }
    }

    // HOTPATH_BENCHMARK=work-iter HOTPATH_CRITERION_ITERATIONS=1000 HOTPATH_OUTPUT_FORMAT=json cargo run -p test-criterion --example fixture --features hotpath,hotpath-cloud -- --exact work/iter
    #[test]
    fn test_cloud_report_names_the_benchmark() {
        let output = fixed("hotpath,hotpath-cloud", "work/iter")
            .json()
            .env("HOTPATH_BENCHMARK", "work-iter")
            .env_remove("HOTPATH_UPLOAD")
            .env_remove("GITHUB_ACTIONS")
            .output();
        assert_success(&output);
        let report = parse_report(&String::from_utf8_lossy(&output.stdout));
        assert_eq!(report.meta.benchmark.as_deref(), Some("work-iter"));
        assert_eq!(report.meta.run, Some(hotpath::json::JsonRun::Native));
        let timing = report.functions_timing.expect("timing section");
        assert_eq!(entry(&timing, ROUTINE).calls, ITERATIONS);
    }

    fn trace(benchmark: &str) -> String {
        let output = Example::new("test-criterion", "batching")
            .env("HOTPATH_CRITERION_ITERATIONS", "25")
            .args(&["--exact", benchmark])
            .output();
        assert_success(&output);
        let stderr = String::from_utf8_lossy(&output.stderr);
        stderr
            .lines()
            .find_map(|l| l.strip_prefix("trace: "))
            .unwrap_or_else(|| panic!("no trace in stderr:\n{stderr}"))
            .to_string()
    }

    fn batches(size: usize, pattern: impl Fn(usize) -> String) -> String {
        (0..25)
            .step_by(size)
            .map(|done| pattern(size.min(25 - done)))
            .collect()
    }

    // HOTPATH_CRITERION_ITERATIONS=25 cargo run -p test-criterion --example batching --features hotpath -- --exact async_batched/value/10
    #[test]
    fn test_batches_follow_criterion() {
        let r = |c: &str, k: usize| c.repeat(k);
        for group in ["batched", "async_batched"] {
            assert_eq!(
                trace(&format!("{group}/value/10")),
                batches(10, |k| r("S", k) + &r("RI", k) + &r("O", k))
            );
            assert_eq!(
                trace(&format!("{group}/ref/10")),
                batches(10, |k| r("S", k) + &r("R", k) + &r("O", k) + &r("I", k))
            );
            assert_eq!(trace(&format!("{group}/value/1")), r("SRIO", 25));
            assert_eq!(trace(&format!("{group}/ref/1")), r("SROI", 25));
        }
    }

    const MERGE_FEATURES: &str = "hotpath,hotpath-alloc,hotpath-callgrind,hotpath-cloud";

    fn merge_run(benchmark: &str, out: &str, callgrind: Option<&RunDir>) -> Example {
        let example = fixed(MERGE_FEATURES, benchmark)
            .release()
            .json()
            .env("HOTPATH_OUTPUT_PATH", out)
            .env("HOTPATH_BENCHMARK", "criterion-fixture")
            .env_remove("HOTPATH_UPLOAD")
            .env_remove("GITHUB_ACTIONS")
            .env_remove("GITHUB_STEP_SUMMARY");
        let Some(dir) = callgrind else {
            return example;
        };
        let out_file = dir.path("cg.%p");
        example.callgrind(&out_file)
    }

    fn read(path: &str) -> JsonReport {
        serde_json::from_str(&std::fs::read_to_string(path).unwrap()).unwrap()
    }

    fn icount(benchmark: &str, dir: &RunDir) -> JsonFunctionsList {
        let out = dir.path(&format!(
            "icount-{}.json",
            dir.0.read_dir().unwrap().count()
        ));
        let output = merge_run(benchmark, &out, Some(dir)).output();
        assert_success(&output);
        assert_eq!(counts(&output).routine_calls, ITERATIONS);
        read(&out).functions_icount.expect("instruction counts")
    }

    // CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER="valgrind -q --tool=callgrind" HOTPATH_CRITERION_ITERATIONS=1000 HOTPATH_OUTPUT_FORMAT=json cargo run --release -p test-criterion --example fixture --features hotpath,hotpath-callgrind -- --exact async/iter_batched
    #[test]
    fn test_callgrind_counts_are_stable() {
        if !valgrind_available() {
            return;
        }
        for benchmark in ["work/iter_batched", "async/iter_batched"] {
            let dir = RunDir::new();
            let first = icount(benchmark, &dir);
            let second = icount(benchmark, &dir);
            let total = |list: &JsonFunctionsList, name: &str| -> u64 {
                let e = entry(list, name);
                assert_eq!(e.calls, ITERATIONS, "{benchmark} {name}");
                e.total.parse().unwrap()
            };
            // A leaf measured function is exact.
            assert_eq!(total(&first, WORK), total(&second, WORK), "{benchmark}");
            // The routine also counts hotpath's own queueing, so it drifts slightly.
            let routine = routine_row(benchmark);
            let (a, b) = (total(&first, routine), total(&second, routine));
            let drift = a.abs_diff(b) as f64 / a as f64;
            assert!(drift < 1e-3, "{benchmark}: routine instructions {a} vs {b}");
        }
    }

    // HOTPATH_CRITERION_ITERATIONS=1000 HOTPATH_OUTPUT_FORMAT=json HOTPATH_OUTPUT_PATH=native.json cargo run --release -p test-criterion --example fixture --features hotpath,hotpath-alloc,hotpath-callgrind,hotpath-cloud -- --exact work/iter_batched
    // CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER="valgrind -q --tool=callgrind" HOTPATH_MERGE_REPORT=native.json HOTPATH_OUTPUT_PATH=merged.json ... (same command)
    #[test]
    fn test_callgrind_run_merges_the_native_report() {
        if !valgrind_available() {
            return;
        }
        for benchmark in ["work/iter_batched", "async/iter_batched"] {
            let dir = RunDir::new();
            let (native_path, merged_path) = (dir.path("native.json"), dir.path("merged.json"));
            let native_output = merge_run(benchmark, &native_path, None).output();
            assert_success(&native_output);
            let output = merge_run(benchmark, &merged_path, Some(&dir))
                .env("HOTPATH_MERGE_REPORT", &native_path)
                .output();
            assert_success(&output);

            let (native, merged) = (read(&native_path), read(&merged_path));
            assert_eq!(merged.meta.run, Some(hotpath::json::JsonRun::Merged));
            assert_eq!(merged.meta.benchmark.as_deref(), Some("criterion-fixture"));
            assert_eq!(
                merged
                    .user_metadata
                    .as_ref()
                    .and_then(|m| m.get("criterion_benchmark"))
                    .map(String::as_str),
                Some(benchmark)
            );
            let timing = merged.functions_timing.as_ref().expect("native timing");
            assert_eq!(
                timing.total_elapsed_ns,
                native.functions_timing.as_ref().unwrap().total_elapsed_ns
            );
            let routine = routine_row(benchmark);
            let alloc = merged.functions_alloc.as_ref().expect("native allocations");
            assert_eq!(bytes(&entry(alloc, routine).avg), 64 + 16, "{benchmark}");
            let icount = merged
                .functions_icount
                .as_ref()
                .expect("instruction counts");
            for list in [timing, alloc, icount] {
                assert_eq!(entry(list, routine).calls, ITERATIONS, "{benchmark}");
                assert_eq!(entry(list, WORK).calls, ITERATIONS, "{benchmark}");
            }
        }
    }
}