On Wed, Sep 5, 2012 at 12:32 PM, Gregory Collins
On recent (>2009) Linux, you can call clock_gettime() with CLOCK_REALTIME_COARSE which is about 6x faster:
https://gist.github.com/3634708
On my workstation calling clock_gettime(CLOCK_REALTIME, ...) and poking the value into a Haskell struct takes about 70ns, with CLOCK_REALTIME_COARSE it's about 19ns (with a much lower stddev). Worth using for this application if it's available. Of course, in Snap we do the "update the clock every second in a thread" trick also.
Of course, I made a rookie mistake here, and can't reproduce the results
because a single call is too short to benchmark accurately. Adding a
replicateM_ 1000 gives:
CLOCK_PROCESS_CPUTIME_ID: 195.0717 ns
CLOCK_REALTIME: 24.92609 ns
CLOCK_REALTIME_COARSE: 14.47882 ns
CLOCK_MONOTONIC: 25.00275 ns
CLOCK_MONOTONIC_COARSE: 15.60754 ns
Updated the gist accordingly.
G
--
Gregory Collins