add shard benchmark experiment (#356)

The current default is 1MB, though previous benchmarks used GB in the
past, so vary the shard size roughly in that range. Each benchmark is
concerned with hash time, as well as manifest time.

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

benchmarks/exp_shard.py

@@ -0,0 +1,91 @@
+# 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 shard parameter."""
+
+import argparse
+import time
+from typing import Final
+
+from google.protobuf import json_format
+import serialize
+
+from model_signing.signing import in_toto
+
+
+KB: Final[int] = 1024
+MB: Final[int] = 1024 * KB
+GB: Final[int] = 1024 * MB
+
+
+def build_parser() -> argparse.ArgumentParser:
+    """Builds the command line parser for the shard experiment."""
+    parser = argparse.ArgumentParser(
+        description="shard 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 shard size",
+        type=int,
+        default=5,
+    )
+
+    parser.add_argument(
+        "--sizes", help="shard sizes to benchmark", nargs="+", type=int
+    )
+
+    return parser
+
+
+def _default_sizes() -> list[int]:
+    sizes = []
+    for scale in [MB, GB]:
+        for d in [1, 2, 5, 10, 20, 50, 100, 200, 500]:
+            if d * scale > 10 * GB:
+                break
+            sizes.append(d * scale)
+    return sizes
+
+
+if __name__ == "__main__":
+    shard_args = build_parser().parse_args()
+
+    shard_sizes = shard_args.sizes or _default_sizes()
+    padding = len(f"{max(shard_sizes)}: ")
+    for shard in shard_sizes:
+        times = []
+        manifest_size = None
+        for _ in range(shard_args.repeat):
+            args = serialize.build_parser().parse_args(
+                [shard_args.path, "--use_shards", f"--shard={shard}"]
+            )
+            st = time.time()
+            payload = serialize.run(args)
+            en = time.time()
+            times.append(en - st)
+
+            if not isinstance(payload, in_toto.IntotoPayload):
+                raise TypeError("IntotoPayloads expected")
+
+            if not manifest_size:
+                statement = json_format.MessageToJson(
+                    payload.statement.pb
+                ).encode("utf-8")
+                manifest_size = len(statement)
+
+        print(f"{f'{shard}: ':<{padding}}{min(times):10.4f} {manifest_size:8}")