HJ Blog > Code Snippet #80: Clock test: G4 vs Xeon+Rosetta vs Xeon

2007-06-18 19:50:52 Clock test: G4 vs Xeon+Rosetta vs Xeon

Interesting benchmarks on a single-threaded loop test in C:

( c ) ✂

#include <time.h>
#include <math.h>
#define N_LOOP 1000000

int main() {
    int i;
    double a = 11234567890123456.0, b;
    clock_t time_1, time_2;
    
    time_1 = clock();
    for (i=0; i<N_LOOP; i++) b = a * a * a * a;
    time_2 = clock();
    printf( "CPU time needed to evaluate a*a*a*a:    %f microsecs\n",
        (double) (time_2 — time_1) / (double) CLOCKS_PER_SEC);
    
    time_1 = clock();
    for (i=0; i<N_LOOP; i++) b = pow( a, 4. );
    time_2 = clock();
    printf( "CPU time needed to evaluate pow(a, 4.): %f microsecs\n",
        (double) (time_2 — time_1) / (double) CLOCKS_PER_SEC);
    
    return 0;
}

  1  #include <time.h>
  2  #include <math.h>
  3  #define N_LOOP 1000000
  4  
  5  int main() {
  6      int i;
  7      double a = 11234567890123456.0, b;
  8      clock_t time_1, time_2;
  9      
 10      time_1 = clock();
 11      for (i=0; i<N_LOOP; i++) b = a * a * a * a;
 12      time_2 = clock();
 13      printf( "CPU time needed to evaluate a*a*a*a:    %f microsecs\n",
 14          (double) (time_2 — time_1) / (double) CLOCKS_PER_SEC);
 15      
 16      time_1 = clock();
 17      for (i=0; i<N_LOOP; i++) b = pow( a, 4. );
 18      time_2 = clock();
 19      printf( "CPU time needed to evaluate pow(a, 4.): %f microsecs\n",
 20          (double) (time_2 — time_1) / (double) CLOCKS_PER_SEC);
 21      
 22      return 0;
 23  }

Here are some benchmarks running this on a 1.5GHz PowerBook G4, then running the binary made on the G4 on a 3GHz Xeon MacPro, then recompiling the code on the MacPro and running again:

CCCCC

	1.5GHz G4	3GHz Xeon / Rosetta	3GHz Xeon native
aaa*a	0.02μs	0.01μs (2x)	0.002341μs (8.54x)
pow(a,4.)	0.29μs	0.08μs (3.6x)	0.065574μs (4.42x)

So, Rosetta gives a speed-up in proportion to the clock speed for the a*a*a*a loop, and a much nicer 3.6x boost for the power function. Recompiling nudges the power function up a hair to 4.42x, but the a's jump to more than 8x the original speed. Interesting stuff. No compiler optimizations were done. Just gcc with no flags set.

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