diff options
Diffstat (limited to 'research/experiments')
3 files changed, 324 insertions, 0 deletions
diff --git a/research/experiments/012-tail-records/2026-09-26-ext4-linux-aarch64.json b/research/experiments/012-tail-records/2026-09-26-ext4-linux-aarch64.json new file mode 100644 index 0000000..457111d --- /dev/null +++ b/research/experiments/012-tail-records/2026-09-26-ext4-linux-aarch64.json @@ -0,0 +1,184 @@ +{ + "rounds": [ + { + "probe": [ + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 2048, + "p50_ms": 2.4, + "p90_ms": 3.11, + "max_ms": 62.79 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 2048, + "p50_ms": 1.23, + "p90_ms": 3.85, + "max_ms": 12.27 + }, + { + "way": "bytes only, fdatasync", + "bytes": 2048, + "p50_ms": 1.23, + "p90_ms": 3.86, + "max_ms": 12.2 + }, + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 8192, + "p50_ms": 2.41, + "p90_ms": 4.51, + "max_ms": 24.86 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 8192, + "p50_ms": 1.57, + "p90_ms": 4.36, + "max_ms": 56.75 + }, + { + "way": "bytes only, fdatasync", + "bytes": 8192, + "p50_ms": 1.18, + "p90_ms": 1.58, + "max_ms": 1.7 + } + ], + "commits": { + "heads in slots": { + "commits_per_second": 220, + "p50_ms": 2.48, + "p90_ms": 5.99, + "p99_ms": 59.68 + }, + "heads as records": { + "commits_per_second": 371, + "p50_ms": 1.29, + "p90_ms": 3.93, + "p99_ms": 52.98 + } + } + }, + { + "probe": [ + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 2048, + "p50_ms": 2.44, + "p90_ms": 5.4, + "max_ms": 13.3 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 2048, + "p50_ms": 1.19, + "p90_ms": 1.76, + "max_ms": 12.16 + }, + { + "way": "bytes only, fdatasync", + "bytes": 2048, + "p50_ms": 1.2, + "p90_ms": 1.56, + "max_ms": 15.32 + }, + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 8192, + "p50_ms": 2.71, + "p90_ms": 8.51, + "max_ms": 23.39 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 8192, + "p50_ms": 1.18, + "p90_ms": 1.6, + "max_ms": 32.89 + }, + { + "way": "bytes only, fdatasync", + "bytes": 8192, + "p50_ms": 1.21, + "p90_ms": 3.9, + "max_ms": 74.29 + } + ], + "commits": { + "heads as records": { + "commits_per_second": 372, + "p50_ms": 1.29, + "p90_ms": 4.04, + "p99_ms": 30.55 + }, + "heads in slots": { + "commits_per_second": 229, + "p50_ms": 2.52, + "p90_ms": 5.54, + "p99_ms": 61.86 + } + } + }, + { + "probe": [ + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 2048, + "p50_ms": 2.44, + "p90_ms": 3.94, + "max_ms": 53.75 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 2048, + "p50_ms": 1.21, + "p90_ms": 1.85, + "max_ms": 4.43 + }, + { + "way": "bytes only, fdatasync", + "bytes": 2048, + "p50_ms": 1.21, + "p90_ms": 1.57, + "max_ms": 4.0 + }, + { + "way": "bytes, head in a slot at the start, fdatasync", + "bytes": 8192, + "p50_ms": 2.4, + "p90_ms": 3.15, + "max_ms": 36.75 + }, + { + "way": "head just before the bytes, fdatasync", + "bytes": 8192, + "p50_ms": 1.21, + "p90_ms": 4.48, + "max_ms": 33.15 + }, + { + "way": "bytes only, fdatasync", + "bytes": 8192, + "p50_ms": 1.12, + "p90_ms": 1.56, + "max_ms": 32.79 + } + ], + "commits": { + "heads in slots": { + "commits_per_second": 233, + "p50_ms": 2.55, + "p90_ms": 6.04, + "p99_ms": 34.19 + }, + "heads as records": { + "commits_per_second": 396, + "p50_ms": 1.26, + "p90_ms": 3.9, + "p99_ms": 28.43 + } + } + } + ] +} diff --git a/research/experiments/012-tail-records/probe.c b/research/experiments/012-tail-records/probe.c new file mode 100644 index 0000000..83c1ed6 --- /dev/null +++ b/research/experiments/012-tail-records/probe.c @@ -0,0 +1,71 @@ +#define _GNU_SOURCE +/* What a small commit's sync costs by where its head goes, on one device: + * a commit of SIZE bytes written over zeros written earlier (no new size or + * blocks, so no journal commit), 40 times per way. The ways run round-robin + * so device drift reaches all of them alike. + * probe DIRECTORY [SIZE] -> one JSON object per way (milliseconds). */ +#include <fcntl.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <time.h> +#include <unistd.h> + +static double now_ms(void) { + struct timespec t; + clock_gettime(CLOCK_MONOTONIC, &t); + return t.tv_sec * 1e3 + t.tv_nsec / 1e6; +} +static int order(const void *a, const void *b) { + double x = *(const double *)a, y = *(const double *)b; + return x < y ? -1 : x > y; +} +enum { WAYS = 3, ROUNDS = 40, HEAD = 128, DATA = 8192 }; +static const char *names[WAYS] = { + "bytes, head in a slot at the start, fdatasync", + "head just before the bytes, fdatasync", + "bytes only, fdatasync", +}; +int main(int argc, char **argv) { + const char *directory = argc > 1 ? argv[1] : "/var/tmp"; + size_t size = argc > 2 ? (size_t)atoi(argv[2]) : 8192; + char path[WAYS][512]; + int fd[WAYS]; + off_t end[WAYS]; + char *bytes = malloc(size), head[HEAD]; + if (!bytes) return 1; + memset(bytes, 'r', size); + for (int w = 0; w < WAYS; ++w) { + snprintf(path[w], sizeof(path[w]), "%s/pure-record-probe-%d", directory, w); + fd[w] = open(path[w], O_RDWR | O_CREAT | O_TRUNC, 0600); + if (fd[w] < 0) return 1; + size_t zeros_size = DATA + (size_t)(ROUNDS + 2) * (size + HEAD); + char *zeros = calloc(1, zeros_size); + if (!zeros || pwrite(fd[w], zeros, zeros_size, 0) != (ssize_t)zeros_size) return 1; + free(zeros); + fsync(fd[w]); + end[w] = DATA; + } + double t[WAYS][ROUNDS]; + for (int r = 0; r < ROUNDS; ++r) + for (int w = 0; w < WAYS; ++w) { + memset(head, 'h' + r % 2, sizeof(head)); + double start = now_ms(); + if (w == 1 && pwrite(fd[w], head, HEAD, end[w]) != HEAD) return 1; + off_t at = end[w] + (w == 1 ? HEAD : 0); + if (pwrite(fd[w], bytes, size, at) != (ssize_t)size) return 1; + end[w] = at + (off_t)size; + if (w == 0 && pwrite(fd[w], head, HEAD, (r % 2) * 4096) != HEAD) return 1; + fdatasync(fd[w]); + t[w][r] = now_ms() - start; + } + for (int w = 0; w < WAYS; ++w) { + qsort(t[w], ROUNDS, sizeof(double), order); + printf("{\"way\":\"%s\",\"bytes\":%zu,\"p50_ms\":%.2f,\"p90_ms\":%.2f,\"max_ms\":%.2f}\n", names[w], size, + t[w][ROUNDS / 2], t[w][ROUNDS * 9 / 10], t[w][ROUNDS - 1]); + close(fd[w]); + unlink(path[w]); + } + free(bytes); + return 0; +} diff --git a/research/experiments/012-tail-records/run.py b/research/experiments/012-tail-records/run.py new file mode 100755 index 0000000..7fc342e --- /dev/null +++ b/research/experiments/012-tail-records/run.py @@ -0,0 +1,69 @@ +#!/usr/bin/env python3 +"""Commit cost by where the head goes (see docs/research/081-tail-records.md). + +Runs probe.c (a small commit's sync with its head in a slot at the start, or +just before its bytes) for 2 KiB and 8 KiB commits, and ../010-one-sync-commit +/commits.c (tree store commit latency) built against the store of --before +(heads in slots) and the current one (heads as records before the bytes), +alternating their order per round so device drift reaches both alike. Prints +one JSON document. +""" +import argparse +import json +import shutil +import subprocess +import sys +import tempfile +from pathlib import Path + +HERE = Path(__file__).resolve().parent +ROOT = HERE.parents[2] +PURE = ROOT / 'prototypes' / 'connections' +COMMITS = HERE.parent / '010-one-sync-commit' / 'commits.c' + + +def build(output, sources): + subprocess.run(['cc', '-O2', '-std=c17', f'-I{PURE}', '-o', str(output)] + [str(s) for s in sources] + ['-lpthread'], + check=True) + + +def main(): + parser = argparse.ArgumentParser() + parser.add_argument('--directory', type=Path, default=Path('/var/tmp'), help='on the device to measure') + parser.add_argument('--before', default='2ef0d40', help='a revision with heads in slots') + parser.add_argument('--rounds', type=int, default=3) + parser.add_argument('--commits', type=int, default=400) + args = parser.parse_args() + with tempfile.TemporaryDirectory() as work: + work = Path(work) + before = work / 'store-tree-before.c' + before.write_text(subprocess.run(['git', '-C', str(ROOT), 'show', f'{args.before}:prototypes/connections/store-tree.c'], + capture_output=True, text=True, check=True).stdout) + build(work / 'probe', [HERE / 'probe.c']) + builds = {'heads in slots': work / 'commits-before', 'heads as records': work / 'commits-after'} + build(builds['heads in slots'], [COMMITS, before]) + build(builds['heads as records'], [COMMITS, PURE / 'store-tree.c']) + results = {'rounds': []} + for round_ in range(args.rounds): + measured = {'probe': [], 'commits': {}} + for size in (2048, 8192): + probe = subprocess.run([str(work / 'probe'), str(args.directory), str(size)], capture_output=True, + text=True, check=True) + measured['probe'] += [json.loads(line) for line in probe.stdout.splitlines()] + names = list(builds) if round_ % 2 == 0 else list(builds)[::-1] + for name in names: + store = Path(tempfile.mkdtemp(dir=args.directory, prefix='pure-commit-cost-')) + shutil.rmtree(store) + try: + run = subprocess.run([str(builds[name]), str(store), str(args.commits)], capture_output=True, text=True, + check=True) + measured['commits'][name] = json.loads(run.stdout) + finally: + shutil.rmtree(store, ignore_errors=True) + results['rounds'].append(measured) + print(json.dumps(measured), file=sys.stderr, flush=True) + print(json.dumps(results, indent=1)) + + +if __name__ == '__main__': + sys.exit(main()) |