Best timing method in C?

Question

What is the best way to time a code section with high resolution and portability?

/* Time from here */
ProcessIntenseFunction();
/* to here. */

printf("Time taken %d seconds %d milliseconds", sec, msec);

Is there a standard library that would have a cross-platform solution?

Answer 1

I use SDL_GetTicks from the SDL library.

Answer 2

I think this should work:

#include <time.h>

clock_t start = clock(), diff;
ProcessIntenseFunction();
diff = clock() - start;

int msec = diff * 1000 / CLOCKS_PER_SEC;
printf("Time taken %d seconds %d milliseconds", msec/1000, msec%1000);

Answer 3

gettimeofday will return time accurate to microseconds within the resolution of the system clock. You might also want to check out the High Res Timers project on SourceForge.

Answer 4

gettimeofday() will probably do what you want.

If you're on Intel hardware, here's how to read the CPU real-time instruction counter. It will tell you the number of CPU cycles executed since the processor was booted. This is probably the finest-grained, lowest overhead counter you can get for performance measurement.

Note that this is the number of CPU cycles. On linux you can get the CPU speed from /proc/cpuinfo and divide to get the number of seconds. Converting this to a double is quite handy.

When I run this on my box, I get

11867927879484732
11867927879692217
it took this long to call printf: 207485

Here's the Intel developer's guide that gives tons of detail.

#include <stdio.h>
#include <stdint.h>

inline uint64_t rdtsc() {
    uint32_t lo, hi;
    __asm__ __volatile__ (
      "xorl %%eax, %%eax\n"
      "cpuid\n"
      "rdtsc\n"
      : "=a" (lo), "=d" (hi)
      :
      : "%ebx", "%ecx");
    return (uint64_t)hi << 32 | lo;
}

main()
{
    unsigned long long x;
    unsigned long long y;
    x = rdtsc();
    printf("%lld\n",x);
    y = rdtsc();
    printf("%lld\n",y);
    printf("it took this long to call printf: %lld\n",y-x);
}