add chunk size experiment (#341)

* add chunk size experiment

So far, the experiment has shown similar results on two different
machines (ARM64 macOS and x86 Linux), and on two different models.

Two factors may limit what models can be benchmarked:
1. Special size of 0, which will attempt to read whole files into
   memory.
2. `timeit.timeit` disables garbage collection, so even if smaller
   buffers are used, older ones may stay around in memory.

The hashing algorithm was left as SHA256 based on the results from the
hashing experiment.

Signed-off-by: Spencer Schrock <[email protected]>

* avoid invalid pytype directive syntax

Signed-off-by: Spencer Schrock <[email protected]>

---------

Signed-off-by: Spencer Schrock <[email protected]>

benchmarks/exp_chunk.py

@@ -0,0 +1,70 @@
+# Copyright 2025 The Sigstore Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+"""Script for running a benchmark to pick a chunk parameter."""
+
+import argparse
+import timeit
+
+import serialize
+
+
+def build_parser() -> argparse.ArgumentParser:
+    """Builds the command line parser for the chunk experiment."""
+    parser = argparse.ArgumentParser(
+        description="chunk size benchmark data for model signing"
+    )
+
+    parser.add_argument("path", help="path to model")
+
+    parser.add_argument(
+        "--repeat",
+        help="how many times to repeat each chunk size",
+        type=int,
+        default=5,
+    )
+
+    parser.add_argument(
+        "--sizes", help="chunk sizes to benchmark", nargs="+", type=int
+    )
+
+    return parser
+
+
+def _default_sizes() -> list[int]:
+    # 0 is a special value to (attempt to) read whole files into RAM
+    # then powers of 2 between 1KB and 1GB
+
+    # https://github.com/google/pytype/issues/795
+    # pytype: disable=bad-return-type
+    return [0] + [2**i for i in range(10, 31)]
+    # pytype: enable=bad-return-type
+
+
+if __name__ == "__main__":
+    chunk_args = build_parser().parse_args()
+
+    chunk_sizes = chunk_args.sizes or _default_sizes()
+    padding = len(f"{max(chunk_sizes)}: ")
+    for chunk_size in chunk_sizes:
+        args = serialize.build_parser().parse_args(
+            [chunk_args.path, f"--chunk={chunk_size}"]
+        )
+        times = timeit.repeat(
+            lambda args=args: serialize.run(args),
+            number=1,
+            repeat=chunk_args.repeat,
+        )
+        print(f"{f'{chunk_size}: ':<{padding}}{min(times):10.4f}")

pyproject.toml

@@ -71,6 +71,8 @@ python = ["3.9", "3.10", "3.11", "3.12", "3.13"]
 description = """Custom environment for running benchmarks.
 Use `hatch run +py=3... bench:generate ${args}` to generate test models.
 Use `hatch run +py=3... bench:serialize ${args}` to benchmark serialization code.
+Use `hatch run +py=3... bench:hash ${args}` to benchmark hashing code.
+Use `hatch run +py=3... bench:chunk ${args}` to benchmark the chunk size parameter.
 """
 extra-dependencies = [
   "numpy",
@@ -83,6 +85,7 @@ python = ["3.9", "3.10", "3.11", "3.12", "3.13"]
 generate = "python benchmarks/generate.py {args}"
 serialize = "python benchmarks/serialize.py {args}"
 hash = "python benchmarks/exp_hash.py {args}"
+chunk = "python benchmarks/exp_chunk.py {args}"
 
 [tool.hatch.envs.docs]
 description = """Custom environment for pdoc.