add script for measuring build performance

1 files changed, 54 insertions, 0 deletions

diff --git a/misc/measure.py b/misc/measure.py
new file mode 100755
index 0000000..1323fc6
--- /dev/null
+++ b/misc/measure.py
@@ -0,0 +1,54 @@
+#!/usr/bin/env python
+
+# Copyright 2011 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""measure the runtime of a command by repeatedly running it.
+"""
+
+import time
+import subprocess
+import sys
+
+devnull = open('/dev/null', 'w')
+
+def run(cmd, repeat=10):
+    print 'sampling:',
+    sys.stdout.flush()
+
+    samples = []
+    for _ in range(repeat):
+        start = time.time()
+        subprocess.call(cmd, stdout=devnull, stderr=devnull)
+        end = time.time()
+        dt = (end - start) * 1000
+        print '%dms' % int(dt),
+        sys.stdout.flush()
+        samples.append(dt)
+    print
+
+    # We're interested in the 'pure' runtime of the code, which is
+    # conceptually the smallest time we'd see if we ran it enough times
+    # such that it got the perfect time slices / disk cache hits.
+    best = min(samples)
+    # Also print how varied the outputs were in an attempt to make it
+    # more obvious if something has gone terribly wrong.
+    err = sum(s - best for s in samples) / float(len(samples))
+    print 'estimate: %dms (mean err %.1fms)' % (best, err)
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        print 'usage: measure.py command args...'
+        sys.exit(1)
+    run(cmd=sys.argv[1:])