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#!/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:])
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