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188 строки
3.9 KiB
188 строки
3.9 KiB
#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/times.h>
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#include <string.h>
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#include "clock.h"
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/* Keep track of most recent reading of cycle counter */
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static unsigned cyc_hi = 0;
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static unsigned cyc_lo = 0;
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void access_counter(unsigned *hi, unsigned *lo)
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{
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/* Get cycle counter */
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asm("rdtsc; movl %%edx,%0; movl %%eax,%1"
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: "=r" (*hi), "=r" (*lo)
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: /* No input */
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: "%edx", "%eax");
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}
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void start_counter()
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{
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access_counter(&cyc_hi, &cyc_lo);
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}
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double get_counter()
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{
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unsigned ncyc_hi, ncyc_lo;
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unsigned hi, lo, borrow;
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double result;
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/* Get cycle counter */
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access_counter(&ncyc_hi, &ncyc_lo);
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/* Do double precision subtraction */
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lo = ncyc_lo - cyc_lo;
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borrow = lo > ncyc_lo;
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hi = ncyc_hi - cyc_hi - borrow;
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result = (double) hi * (1 << 30) * 4 + lo;
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if (result < 0) {
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fprintf(stderr, "Error: Cycle counter returning negative value: %.0f\n", result);
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}
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return result;
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}
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double ovhd()
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{
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/* Do it twice to eliminate cache effects */
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int i;
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double result;
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for (i = 0; i < 2; i++) {
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start_counter();
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result = get_counter();
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}
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return result;
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}
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/* Keep track of clock speed */
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double cpu_ghz = 0.0;
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/* Get megahertz from /etc/proc */
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#define MAXBUF 512
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double core_mhz(int verbose) {
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static char buf[MAXBUF];
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FILE *fp = fopen("/proc/cpuinfo", "r");
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cpu_ghz = 0.0;
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if (!fp) {
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fprintf(stderr, "Can't open /proc/cpuinfo to get clock information\n");
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cpu_ghz = 1.0;
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return cpu_ghz * 1000.0;
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}
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while (fgets(buf, MAXBUF, fp)) {
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if (strstr(buf, "cpu MHz")) {
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double cpu_mhz = 0.0;
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sscanf(buf, "cpu MHz\t: %lf", &cpu_mhz);
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cpu_ghz = cpu_mhz / 1000.0;
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break;
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}
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}
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fclose(fp);
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if (cpu_ghz == 0.0) {
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fprintf(stderr, "Can't open /proc/cpuinfo to get clock information\n");
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cpu_ghz = 1.0;
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return cpu_ghz * 1000.0;
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}
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if (verbose) {
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printf("Processor Clock Rate ~= %.4f GHz (extracted from file)\n", cpu_ghz);
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}
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return cpu_ghz * 1000;
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}
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double mhz(int verbose) {
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double val = core_mhz(verbose);
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return val;
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}
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/* Determine clock rate by measuring cycles
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elapsed while sleeping for sleeptime seconds */
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double mhz_full(int verbose, int sleeptime)
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{
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double rate;
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start_counter();
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sleep(sleeptime);
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rate = get_counter()/(1e6*sleeptime);
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if (verbose)
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printf("Processor Clock Rate ~= %.1f MHz\n", rate);
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return rate;
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}
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///* Version using a default sleeptime */
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//double mhz(int verbose)
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//{
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// return mhz_full(verbose, 2);
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//}
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/** Special counters that compensate for timer interrupt overhead */
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static double cyc_per_tick = 0.0;
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#define NEVENT 100
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#define THRESHOLD 1000
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#define RECORDTHRESH 3000
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/* Attempt to see how much time is used by timer interrupt */
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static void callibrate(int verbose)
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{
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double oldt;
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struct tms t;
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clock_t oldc;
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int e = 0;
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times(&t);
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oldc = t.tms_utime;
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start_counter();
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oldt = get_counter();
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while (e <NEVENT) {
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double newt = get_counter();
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if (newt-oldt >= THRESHOLD) {
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clock_t newc;
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times(&t);
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newc = t.tms_utime;
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if (newc > oldc) {
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double cpt = (newt-oldt)/(newc-oldc);
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if ((cyc_per_tick == 0.0 || cyc_per_tick > cpt) && cpt > RECORDTHRESH)
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cyc_per_tick = cpt;
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/*
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if (verbose)
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printf("Saw event lasting %.0f cycles and %d ticks. Ratio = %f\n",
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newt-oldt, (int) (newc-oldc), cpt);
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*/
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e++;
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oldc = newc;
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}
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oldt = newt;
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}
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}
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if (verbose)
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printf("Setting cyc_per_tick to %f\n", cyc_per_tick);
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}
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static clock_t start_tick = 0;
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void start_comp_counter() {
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struct tms t;
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if (cyc_per_tick == 0.0)
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callibrate(1);
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times(&t);
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start_tick = t.tms_utime;
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start_counter();
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}
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double get_comp_counter() {
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double time = get_counter();
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double ctime;
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struct tms t;
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clock_t ticks;
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times(&t);
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ticks = t.tms_utime - start_tick;
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ctime = time - ticks*cyc_per_tick;
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/*
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printf("Measured %.0f cycles. Ticks = %d. Corrected %.0f cycles\n",
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time, (int) ticks, ctime);
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*/
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return ctime;
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}
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