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Re: Measuring time intervals using Time::HiRes -- time vs. gettimeofday and tv_interval

by shonorio (Hermit)
on Jul 18, 2006 at 19:14 UTC ( #562104=note: print w/replies, xml ) Need Help??


in reply to Measuring time intervals using Time::HiRes -- time vs. gettimeofday and tv_interval

By Benchmark, the second one is faster than the first code. If think you could benchmark you code with both code to be sure.

use Time::HiRes qw(time); use Benchmark qw(:all) ; # Use Perl code in strings... cmpthese(-10, { 'Hires' => sub { my $t0 = [Time::HiRes::gettimeofday]; my $elapsed = Time::HiRes::tv_interval($t0)} , 'Time' => sub { my $t0 = time; my $elapsed = time - $t0; }, });
... result ...
Rate Hires Time Hires 100260/s -- -58% Time 240043/s 139% --
Solli Moreira Honorio
Sao Paulo - Brazil
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Re^2: Measuring time intervals using Time::HiRes -- time vs. gettimeofday and tv_interval
by hrr (Monk) on Jul 18, 2006 at 19:33 UTC
    Thank you for this hint! I obtained similar benchmark results as you did.

    Surprsingly, using Time::HiRes::time instead of the standard time, the performance is much better (but still worse than tv_interval):
    Rate Hires Time Hires 98201/s -- -55% Time 220149/s 124% --
      Vice versa. Look at the Rate column it shows the speed of the function! The more times a second the function is called, the faster it is :) So in this table (produced by the benchmark involving all three variants)
      Rate interval HiRes::time buitin time() interval 88470/s -- -53% -95% HiRes::time 188363/s 113% -- -89% buitin time() 1753092/s 1882% 831% --
      builtin time() is 9 times faster than Time::HiRes::time, which is nearly 2 times faster than the weird variant with tv_interval!

      Benchmark code is here:


           s;;Just-me-not-h-Ni-m-P-Ni-lm-I-ar-O-Ni;;tr?IerONim-?HAcker ?d;print

        As long as we're all tweaking the heck out of our benchmarks... ;-)

        What I've noticed is the number of calls to these functions are not all the same. In the 'interval' function, we are calling gettimeofday, constructing an anonymous array, calling tv_interval, and destroying the array. Only one of these are we actually interested in. Meanwhile, both of the other two cases, we're calling *time twice. A completely different set of comparisons. I also eliminated the overhead of returning floats, what little that should be.

        So, I thought I'd throw this into the mix. Put all the initialisation up front. Then see what happens.

        And the results?
        Rate interval time hires interval 685148/s -- -79% -80% time 3340426/s 388% -- -2% hires 3398163/s 396% 2% --
        2% bonus to hires's time over the built-in time? I'll chalk that up to statistically insignificant, and call the two a tie. In fact, I ran it a second time and got it reversed:
        Rate interval hires time interval 971246/s -- -77% -78% hires 4192706/s 332% -- -3% time 4327848/s 346% 3% --
        So, I'd say that the difference between interval and time is non-trivial. But even that operates fast enough that I'm not going to worry about it.

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