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Timing Your Code {#timing}
================
timer() : A platform-independent timer with microsecond accuracy:
* [timer::start()](\ref af::timer::start) starts a timer
* [timer::start()](\ref af::timer::stop) seconds since last \ref af::timer::start "start"
* \ref af::timer::stop(af::timer start) "timer::start(timer start)" seconds since 'start'
Example: single timer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
// start timer
timer::start();
// run your code
printf("elapsed seconds: %g\n", timer::stop());
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Example: multiple timers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
// start timers
timer start1 = timer::start();
timer start2 = timer::start();
// run some code
printf("elapsed seconds: %g\n", timer::stop(start1));
// run more code
printf("elapsed seconds: %g\n", timer::stop(start2));
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Accurate and reliable measurement of performance involves several factors:
* Executing enough iterations to achieve peak performance.
* Executing enough repetitions to amortize any overhead from system timers.
To take care of much of this boilerplate, [timeit](\ref af::timeit) provides
accurate and reliable estimates of both CPU or GPU code.
Here`s a stripped down example of
[Monte-Carlo estimation of PI](\ref benchmarks/pi.cpp) making use
of [timeit](\ref af::timeit). Notice how it expects a `void` function pointer.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
#include <stdio.h>
#include <arrayfire.h>
using namespace af;
void pi_function() {
int n = 20e6; // 20 million random samples
array x = randu(n,f32), y = randu(n,f32);
// how many fell inside unit circle?
float pi = 4.0 * sum<float>(sqrt(x*x + y*y)) < 1) / n;
}
int main() {
printf("pi_function took %g seconds\n", timeit(pi_function));
return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This produces:
pi_function took 0.007252 seconds
(test machine: Core i7 920 @ 2.67GHz with a Tesla C2070)
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