OT: recommended way of timing two pieces of code in C
Ranjan Maitra
maitra.mbox.ignored at inbox.com
Sat Feb 27 14:48:23 UTC 2016
On Sat, 27 Feb 2016 14:09:25 +0000 "Patrick O'Callaghan" <pocallaghan at gmail.com> wrote:
> On Sat, 2016-02-27 at 07:44 -0600, Ranjan Maitra wrote:
> > #define INTERVAL 1 /* number of milliseconds to go off */
> >
> > int main() {
> > double sum = 0;
> > struct itimerval initial, updated;
> >
> > initial.it_value.tv_sec = INTERVAL/1000000;
> > initial.it_value.tv_usec = (INTERVAL/1000000) * 1000000;
>
> To start with, these are both integer values, so you're initializing
> them to 0. There may be other bugs but I stopped looking when I saw
> this.
>
> poc
> --
OK, thanks! So, I tried this:
#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#define INTERVAL 1 /* number of milliseconds to go off */
int main() {
double sum = 0;
struct itimerval initial, updated;
initial.it_value.tv_sec = INTERVAL;
initial.it_value.tv_usec = INT_MAX;
initial.it_interval = initial.it_value;
printf("%ld\n", initial.it_value.tv_usec);
if (setitimer(ITIMER_VIRTUAL, &initial, NULL) == -1) {
perror("error calling setitimer()");
exit(1);
}
for (unsigned int i; i < 100000; i++)
sum += 1./i;
if (getitimer(ITIMER_REAL, &updated) == -1) {
perror("error calling getitimer()");
exit(1);
}
printf("Time started = %ld\n; Time taken = %ld\n: Time taken = %ld\n",
initial.it_value.tv_usec, updated.it_value.tv_usec,
initial.it_value.tv_usec - updated.it_value.tv_usec);
return 0;
}
But now setitimer does not execute:-(
$gcc -o timer -std=c99 -Wall -pedantic getitimer.c -lrt -O3
$./timer
2147483647
error calling setitimer(): Invalid argument
Thanks!
Ranjan
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