Compare durable writes on a device in the same state

An SD card slows down under sustained syncs, so the order of runs alone
changed write results several times over. The HTTP benchmark now repeats
rounds with the servers in a rotated order, gives every run a fresh store,
times the device (an in-place 4 KiB write + fdatasync) before each write
workload and reports medians over rounds with the probe range beside them.
--workloads picks workloads by label prefix.

1 files changed, 81 insertions, 37 deletions

diff --git a/benchmarks/http/run.py b/benchmarks/http/run.py
index 8ce1474..f9fdbc0 100644
--- a/benchmarks/http/run.py
+++ b/benchmarks/http/run.py
@@ -4,7 +4,15 @@ same contract, on the same machine, with the same load generator.
 
 Servers are pinned to CPUs 0-2 and the load to CPU 3; stores live under
 --directory (use the device you care about: fsync costs are the device's).
-Prints one JSON object per (server, workload) and a summary table.
+Prints one JSON object per (server, workload, round) and a summary table of
+medians over rounds.
+
+Durable writes are only comparable on a device in the same state. An SD card
+slows down under sustained syncs, so the order of runs alone can change a
+result several times over. Each round therefore runs the servers in a
+rotated order, each on a fresh store, and every write workload first times
+the device (an in-place 4 KiB write + fdatasync); the table shows that probe
+next to each result.
 """
 import argparse
 import json
@@ -12,6 +20,7 @@ import os
 import select
 import shutil
 import signal
+import statistics
 import struct
 import subprocess
 import sys
@@ -51,6 +60,25 @@ def put(port, key, body, expected):
     assert response.status == 200, (key, response.status)
 
 
+def probe_ms(directory, count=16):
+    """Median time of an in-place 4 KiB write + fdatasync on the store device."""
+    path = directory / 'device-probe'
+    fd = os.open(path, os.O_RDWR | os.O_CREAT | os.O_TRUNC, 0o600)
+    try:
+        os.pwrite(fd, bytes(count * 4096), 0)
+        os.fsync(fd)
+        times = []
+        for i in range(count):
+            start = time.perf_counter()
+            os.pwrite(fd, b'p' * 4096, i * 4096)
+            os.fdatasync(fd)
+            times.append((time.perf_counter() - start) * 1e3)
+    finally:
+        os.close(fd)
+        path.unlink()
+    return round(statistics.median(times), 2)
+
+
 def load(port, connections, seconds, method, keys, mode, body=16):
     output = subprocess.run(['taskset', '-c', '3', str(HERE / 'load'), str(port), str(connections), str(seconds),
                              method, str(keys), mode, str(body)], capture_output=True, text=True, check=True)
@@ -63,6 +91,9 @@ def main():
     parser.add_argument('--directory', type=Path, default=Path('/var/tmp'))
     parser.add_argument('--seconds', type=float, default=5)
     parser.add_argument('--only', default='')
+    parser.add_argument('--workloads', default='', help='run only workloads whose label starts with one of these')
+    parser.add_argument('--rounds', type=int, default=1, help='repeat every server, rotating their order')
+    parser.add_argument('--pause', type=float, default=0, help='seconds to rest the device between runs')
     parser.add_argument('--budget', type=int, default=64 << 20, help="Pure's payload budget in bytes")
     args = parser.parse_args()
     axum = HERE / 'axum-baseline/target/release/axum-baseline'
@@ -85,50 +116,63 @@ def main():
         ('put 16B, 64 conn, keep-alive', dict(connections=64, method='put', keys=64, mode='keep-alive')),
         ('put 16B, 8 conn, keep-alive', dict(connections=8, method='put', keys=8, mode='keep-alive')),
     ]
+    if args.workloads:
+        workloads = [w for w in workloads if w[0].startswith(tuple(args.workloads.split(',')))]
+    chosen = [name for name in servers if not args.only or name in args.only.split(',')]
     results = []
     try:
-        for name, command in servers.items():
-            if args.only and name not in args.only.split(','):
-                continue
-            directory = base / name
-            process, port = start(command(directory))
-            idle = rss_kib(process.pid, 'VmRSS:')
-            for key in range(64):
-                put(port, f'k{key}', b'x' * 56, 0)
-            big = b'B' * (1 << 20)
-            put(port, 'big', big, 0)
-            for label, workload in workloads:
-                keys = workload['keys']
-                if workload.get('big'):
-                    # the 1 MiB document is k0 for this workload
-                    put(port, 'k0', big, 1)
-                if workload['method'] == 'put':
-                    # fresh keys per run so every connection starts at If-None-Match: *
-                    pass
-                measured = load(port, workload['connections'], args.seconds, workload['method'], keys,
-                                workload['mode'])
-                measured.update(server=name, workload=label, rss_kib=rss_kib(process.pid, 'VmRSS:'),
-                                ok_per_second=round(measured['2xx'] / args.seconds))
-                results.append(measured)
-                print(json.dumps(measured), flush=True)
-            peak = rss_kib(process.pid, 'VmHWM:')
-            process.send_signal(signal.SIGINT if name.startswith('axum') else signal.SIGTERM)
-            process.communicate(timeout=30)
-            for r in results:
-                if r['server'] == name:
-                    r['idle_rss_kib'], r['peak_rss_kib'] = idle, peak
+        for round_ in range(args.rounds):
+            turn = round_ % len(chosen)
+            for name in chosen[turn:] + chosen[:turn]:
+                if args.pause:
+                    time.sleep(args.pause)
+                directory = base / f'{name}-{round_}'
+                process, port = start(servers[name](directory))
+                idle = rss_kib(process.pid, 'VmRSS:')
+                for key in range(64):
+                    put(port, f'k{key}', b'x' * 56, 0)
+                for label, workload in workloads:
+                    if workload.get('big'):
+                        # the 1 MiB document is k0 for this workload
+                        put(port, 'k0', b'B' * (1 << 20), 1)
+                    probe = probe_ms(base) if workload['method'] == 'put' else None
+                    measured = load(port, workload['connections'], args.seconds, workload['method'],
+                                    workload['keys'], workload['mode'])
+                    measured.update(server=name, workload=label, round=round_, probe_ms=probe,
+                                    rss_kib=rss_kib(process.pid, 'VmRSS:'),
+                                    ok_per_second=round(measured['2xx'] / args.seconds), idle_rss_kib=idle)
+                    results.append(measured)
+                    print(json.dumps(measured), flush=True)
+                peak = rss_kib(process.pid, 'VmHWM:')
+                process.send_signal(signal.SIGINT if name.startswith('axum') else signal.SIGTERM)
+                process.communicate(timeout=30)
+                shutil.rmtree(directory, ignore_errors=True)
+                for r in results:
+                    if r['server'] == name and r['round'] == round_:
+                        r['peak_rss_kib'] = peak
     finally:
         shutil.rmtree(base, ignore_errors=True)
+    median = lambda rows, field: statistics.median(r[field] for r in rows)
     print()
-    print(f"{'workload':32s} {'server':14s} {'2xx/s':>9s} {'p50 us':>8s} {'p99 us':>8s} {'errors':>7s} {'non-2xx':>8s}")
-    for r in results:
-        print(f"{r['workload']:32s} {r['server']:14s} {r['ok_per_second']:9d} {r['p50_us']:8d} {r['p99_us']:8d} "
-              f"{r['errors']:7d} {r['4xx'] + r['5xx']:8d}")
+    print(f"medians over {args.rounds} round(s)")
+    print(f"{'workload':32s} {'server':14s} {'2xx/s':>9s} {'p50 us':>8s} {'p99 us':>8s} {'errors':>7s} "
+          f"{'non-2xx':>8s} {'probe ms':>9s}")
+    for label, _ in workloads:
+        for name in chosen:
+            rows = [r for r in results if r['server'] == name and r['workload'] == label]
+            if not rows:
+                continue
+            probes = [r['probe_ms'] for r in rows if r['probe_ms'] is not None]
+            probe = f"{min(probes):.1f}-{max(probes):.1f}" if probes else '-'
+            print(f"{label:32s} {name:14s} {median(rows, 'ok_per_second'):9.0f} {median(rows, 'p50_us'):8.0f} "
+                  f"{median(rows, 'p99_us'):8.0f} {sum(r['errors'] for r in rows):7d} "
+                  f"{sum(r['4xx'] + r['5xx'] for r in rows):8d} {probe:>9s}")
     print()
-    for name in servers:
+    for name in chosen:
         rows = [r for r in results if r['server'] == name]
         if rows:
-            print(f"{name:14s} idle RSS {rows[0]['idle_rss_kib']} KiB, peak RSS {rows[0]['peak_rss_kib']} KiB")
+            print(f"{name:14s} idle RSS {median(rows, 'idle_rss_kib'):.0f} KiB, "
+                  f"peak RSS {max(r['peak_rss_kib'] for r in rows)} KiB")
 
 
 if __name__ == '__main__':