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copied!<p>Here's a solution for GNU/Linux that uses the x86 CPU timestamp counter:</p> <ul> <li>Caveat: Only works on x86 and non-tickless kernels...</li> <li>Trivia: who can tell us what the timing returned is on a tickless kernel?</li> <li>Hint: it won't be real time</li> </ul> <p>rdtsc.c:</p> <pre><code>#include <sys/time.h> #include <time.h> #include <stdio.h> #include <stdlib.h> #include <string.h> typedef unsigned long long int64; static __inline__ int64 getticks(void) { unsigned a, d; asm volatile("rdtsc" : "=a" (a), "=d" (d)); return (((int64)a) | (((int64)d) << 32)); } int main(){ int64 tick,tick1; unsigned time=0,ut,mt; // ut is the divisor to give microseconds // mt gives milliseconds FILE *pf; int i,r,l,n=0; char s[100]; // time how long it takes to get the divisors, as a test tick = getticks(); // get the divisors - todo: for max performance this can // output a new binary or library with these values hardcoded // for the relevant CPU - a kind-of ludicrous notion considering // that this will only work on x86 compatible cpus anyways where // performance is the least of your issues... // ... curse of the assembly coder ;-) pf = fopen("/proc/cpuinfo","r"); do { r=fscanf(pf,"%s",&s[0]); if (r<0) { n=5; break; } else if (n==0) { if (strcmp("MHz",s)==0) n=1; } else if (n==1) { if (strcmp(":",s)==0) n=2; } else if (n==2) { n=3; }; } while (n<3); fclose(pf); l=strlen(s); s[l-4]=s[l-3]; s[l-3]=s[l-2]; s[l-2]=s[l-1]; s[l-1]=(char)0; mt=atoi(s); s[l-4]=(char)0; ut=atoi(s); printf("%s Mhz - ut = %u, mt = %u // hardcode these for your a CPU-specific binary ;-)\n",s,ut,mt); tick1 = getticks(); time = (unsigned)((tick1-tick)/ut); printf("%u us\n",time); // time the duration of sleep(1) - plus overheads ;-) tick = getticks(); sleep(1); tick1 = getticks(); time = (unsigned)((tick1-tick)/mt); printf("%u ms\n",time); return 0; } </code></pre> <p>compile and run with</p> <blockquote> <p>$ gcc rdtsc.c -o rdtsc && ./rdtsc</p> </blockquote> <p>It reads the correct divisor for your CPU from /proc/cpuinfo and shows how long it took to read that in microseconds, as well as how long it takes to execute sleep(1) in milliseconds.</p> <p>... Assuming the Mhz rating in /proc/cpuinfo always contains 3 decimal places :-o</p>

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