Re: How to measure time for a particular code section?

[zentara]

in reply to How to measure time for a particular code section?

See performance profiling

[abdullah.yildiz]

Thank you for your answer.

[abdullah.yildiz]

Here is my problem: I want to sort 10 million random integers:

$start = Benchmark->new();

#RUN THE ALGORITHM
@sorted_numbers = sort { $a <=> $b } @numbers;

$end = Benchmark->new();
$diff = timediff( $end, $start );

And then it returns: 18 wallclock secs (14.59 usr + 0.97 sys = 15.55 CPU) However it takes much more than that. Could you help me about this? I'm a bit confused. Thank you.

[Anonymous Monk]

"..However it takes much more than that.."
How do you know that?

[abdullah.yildiz]

Thank you for your answer. I meant I waited too much to finish it. Additionally, The code

my $start_time = [Time::HiRes::gettimeofday()];
.
.
.
my ($user, $system, $child_user, $child_system) = times;
print "wall clock time was ", Time::HiRes::tv_interval($start_time), "
+\n",
    "user time for $$ was $user\n",
    "system time for $$ was $system\n",
    "user time for all children was $child_user\n",
    "system time for all children was $child_system\n";

gives different results with respect to benchmark. Sorry for any foolish comments.

[zentara]

I'm a bit confused

Using time to measure code execution is not going to be accurate everytime it is run. What if the load on the cpu is heavier during one test, say for example because a cron job is running, or whatever else is eating up cpu cycles. The only way to really measure code execution, is how many cpu cycles it takes to get the task done, the time taken is a function of many things going on in the computer, from random delays in hard drive access, other processes suddenly using up cpu cycles, and just plain randomness. The way to get a good benchmark, would be to run the test code a thousand times over the course of a day, and take the average time.

See Lies, Damn Lies and Benchmarks and No More Meaningless Benchmarks! for example. You can google for more discussions on the deceptive nature of benchmarks yourself.

[abdullah.yildiz]

Thank you for your suggestions.