How to get cpu cycles between to operations in c program with BBB

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1

Hi all,

I want to measure the number of cpu cycles between two operations in a c program. I am running a BBB rev C.1 on Debian (3.8.13-bone70). My code is pretty simple:

#include <stdio.h>
#include <time.h>

int main(void) {
clock_t start,stop;

start=clock();
`
int j;

for(j=0;j<12345;j++){
; // burn time
}

stop=clock();

printf(“used cycles: %f\n”,(long)(stop-start));

return (0);
}

`

The output is not satisfiing
root@beaglebone:/home/debian# ./getCycles
used cycles: 0.000000

This is the way I always did that in the past as far as I remember. Did I miss something? Maybe like additional support packages? Thank you in advance!

2

The compiler destroyed your for loop probably, because nothing useful is inside.
Try to turn the optimizations off.

Omikron

3

In my productive system I indeed have true operations in the for loop, I just left them out. Also if I print out the value of clock() I also receive a 0.00000. For me it looks like the clock might not be initialized? But don’t know how to enable or initialize it…

4

http://stackoverflow.com/questions/9871071/why-c-clock-returns-0

Google works wonders for questions like these :wink: