1#!/usr/bin/env python3
2
3# Copyright 2011 Google Inc. All Rights Reserved.
4#
5# Licensed under the Apache License, Version 2.0 (the "License");
6# you may not use this file except in compliance with the License.
7# You may obtain a copy of the License at
8#
9#     http://www.apache.org/licenses/LICENSE-2.0
10#
11# Unless required by applicable law or agreed to in writing, software
12# distributed under the License is distributed on an "AS IS" BASIS,
13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14# See the License for the specific language governing permissions and
15# limitations under the License.
16
17"""measure the runtime of a command by repeatedly running it.
18"""
19
20import time
21import subprocess
22import sys
23
24devnull = open('/dev/null', 'w')
25
26def run(cmd, repeat=10):
27    print('sampling:', end=' ')
28    sys.stdout.flush()
29
30    samples = []
31    for _ in range(repeat):
32        start = time.time()
33        subprocess.call(cmd, stdout=devnull, stderr=devnull)
34        end = time.time()
35        dt = (end - start) * 1000
36        print('%dms' % int(dt), end=' ')
37        sys.stdout.flush()
38        samples.append(dt)
39    print()
40
41    # We're interested in the 'pure' runtime of the code, which is
42    # conceptually the smallest time we'd see if we ran it enough times
43    # such that it got the perfect time slices / disk cache hits.
44    best = min(samples)
45    # Also print how varied the outputs were in an attempt to make it
46    # more obvious if something has gone terribly wrong.
47    err = sum(s - best for s in samples) / float(len(samples))
48    print('estimate: %dms (mean err %.1fms)' % (best, err))
49
50if __name__ == '__main__':
51    if len(sys.argv) < 2:
52        print('usage: measure.py command args...')
53        sys.exit(1)
54    run(cmd=sys.argv[1:])
55