[FEAT] Add micro benchmark for comparing built-in hash(), SHA-256, and xxHash from [23673](#23673)

Author: LuminolT

benchmarks/benchmark_hash.py

@@ -0,0 +1,120 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Micro benchmark comparing built-in hash(), SHA-256, and xxHash.
+
+This focuses on a single test payload shaped like the prefix-cache hash input:
+    (32-byte bytes object, 32-int tuple)
+
+Usage:
+    python benchmarks/hash_micro_benchmark.py --iterations 20000
+"""
+
+from __future__ import annotations
+
+import argparse
+import random
+import statistics
+import time
+from typing import Callable, Iterable
+
+from vllm.utils.hashing import sha256, xxhash
+
+
+def _generate_test_data(seed: int) -> tuple[bytes, tuple[int, ...]]:
+    """Generate a deterministic test payload."""
+    random.seed(seed)
+    bytes_data = bytes(random.getrandbits(8) for _ in range(32))
+    int_tuple = tuple(random.randint(1, 1_000_000) for _ in range(32))
+    return (bytes_data, int_tuple)
+
+
+def _benchmark_func(func: Callable[[tuple], object], data: tuple, iterations: int):
+    """Return (avg_seconds, std_seconds) for hashing `data` `iterations` times."""
+    times: list[float] = []
+
+    # Warm-up to avoid first-run noise.
+    for _ in range(200):
+        func(data)
+
+    for _ in range(iterations):
+        start = time.perf_counter()
+        func(data)
+        end = time.perf_counter()
+        times.append(end - start)
+
+    avg = statistics.mean(times)
+    std = statistics.stdev(times) if len(times) > 1 else 0.0
+    return avg, std
+
+
+def _run_benchmarks(
+    benchmarks: Iterable[tuple[str, Callable[[tuple], object]]],
+    data: tuple,
+    iterations: int,
+):
+    """Yield (name, avg, std) for each benchmark, skipping unavailable ones."""
+    for name, func in benchmarks:
+        try:
+            avg, std = _benchmark_func(func, data, iterations)
+        except ModuleNotFoundError as exc:
+            print(f"Skipping {name}: {exc}")
+            continue
+        yield name, avg, std
+
+
+def builtin_hash(data: tuple) -> int:
+    """Wrapper for Python's built-in hash()."""
+    return hash(data)
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--iterations",
+        type=int,
+        default=10_000,
+        help="Number of measured iterations per hash function.",
+    )
+    parser.add_argument(
+        "--seed", type=int, default=42, help="Random seed for test payload."
+    )
+    args = parser.parse_args()
+
+    data = _generate_test_data(args.seed)
+    benchmarks = (
+        ("SHA256 (pickle)", sha256),
+        ("xxHash (pickle)", xxhash),
+        ("built-in hash()", builtin_hash),
+    )
+
+    print("=" * 60)
+    print("HASH FUNCTION MICRO BENCHMARK")
+    print("=" * 60)
+    print("Test data: (32-byte bytes object, 32-int tuple)")
+    print(f"Iterations: {args.iterations:,}")
+    print("=" * 60)
+
+    results = list(_run_benchmarks(benchmarks, data, args.iterations))
+    builtin_entry = next((r for r in results if r[0] == "built-in hash()"), None)
+
+    print("\nResults:")
+    for name, avg, std in results:
+        print(f"  {name:16s}: {avg * 1e6:8.2f} ± {std * 1e6:6.2f} μs")
+
+    if builtin_entry:
+        _, builtin_avg, _ = builtin_entry
+        print("\n" + "=" * 60)
+        print("SUMMARY (relative to built-in hash())")
+        print("=" * 60)
+        for name, avg, _ in results:
+            if name == "built-in hash()":
+                continue
+            speed_ratio = avg / builtin_avg
+            print(f"• {name} is {speed_ratio:.1f}x slower than built-in hash()")
+    else:
+        print("\nBuilt-in hash() result missing; cannot compute speed ratios.")
+
+
+if __name__ == "__main__":
+    main()