Script to measure how long the system actually sleeps for, like "ping" for the OS scheduler.

measure_latency.py

"""Measures how long simple I/O requests take, like "ping" for the OS disk I/O scheduler."""

import datetime
import os
import time
from argparse import ArgumentParser
from tempfile import NamedTemporaryFile

interval = 0.5


def main():
    """Measures how long simple I/O requests take, like "ping" for the OS disk I/O scheduler."""
    parser = ArgumentParser(description=__doc__)
    parser.add_argument('dir', help="Directory to create file in")
    args = parser.parse_args()

    with NamedTemporaryFile(dir=args.dir, prefix=os.path.basename(__file__) + '.', suffix='.tmp') as handle:
        while True:
            time.sleep(interval)

            t0 = time.time()
            handle.write(b'a')
            handle.flush()
            os.fsync(handle.fileno())
            t1 = time.time()
            actual = (t1 - t0)

            time_now = datetime.datetime.fromtimestamp(t1)
            # print(f"{time_now.time()}: expected {interval} actual {actual:.4f} overrun {actual - interval:.4f}")
            print(f"{time_now.time()}: {args.dir}: latency {actual:.4f} s")


if __name__ == '__main__':
    main()