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/*
* clock.c - Routines for using the cycle counters on x86
*
* Copyright (c) 2002, R. Bryant and D. O'Hallaron, All rights reserved.
* May not be used, modified, or copied without permission.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/times.h>
#include "clock.h"
/*******************************************************
* Machine dependent functions
*
* Note: the constants __i386__ and __x86_64__
* are set by GCC when it calls the C preprocessor
* You can verify this for yourself using gcc -v.
*******************************************************/
#if defined(__i386__) || defined(__x86_64__)
/*******************************************************
* Pentium versions of start_counter() and get_counter()
*******************************************************/
/* $begin x86cyclecounter */
/* Initialize the cycle counter */
static unsigned cyc_hi = 0;
static unsigned cyc_lo = 0;
/* Set *hi and *lo to the high and low order bits of the cycle counter.
Implementation requires assembly code to use the rdtsc instruction. */
void access_counter(unsigned *hi, unsigned *lo)
{
asm("rdtsc" /* Put cycle counter in %edx:%eax */
: "=d" (*hi), "=a" (*lo));
}
/* Record the current value of the cycle counter. */
void start_counter()
{
access_counter(&cyc_hi, &cyc_lo);
}
/* Return the number of cycles since the last call to start_counter. */
double get_counter()
{
unsigned ncyc_hi, ncyc_lo;
unsigned hi, lo, borrow;
double result;
/* Get cycle counter */
access_counter(&ncyc_hi, &ncyc_lo);
/* Do double precision subtraction */
lo = ncyc_lo - cyc_lo;
borrow = lo > ncyc_lo;
hi = ncyc_hi - cyc_hi - borrow;
result = (double) hi * (1 << 30) * 4 + lo;
if (result < 0) {
fprintf(stderr, "Error: counter returns neg value: %.0f\n", result);
}
return result;
}
/* $end x86cyclecounter */
#else
#error Timer code requires x86
#endif
/*******************************
* Machine-independent functions
******************************/
/* $begin mhz */
/* Get the clock rate from /proc */
double mhz_full(int verbose, int sleeptime)
{
(void) sleeptime;
FILE *fp = fopen("/proc/cpuinfo", "r");
// Hack to keep this working on labradoodle.
double mhz = 2000.0;
fclose(fp);
if (verbose)
printf("Processor clock rate ~= %.1f MHz\n", mhz);
return mhz;
#if 0
double rate;
start_counter();
sleep(sleeptime);
rate = get_counter() / (1e6*sleeptime);
if (verbose)
printf("Processor clock rate ~= %.1f MHz\n", rate);
return rate;
#endif
}
/* $end mhz */
/* Version using a default sleeptime */
double mhz(int verbose)
{
return mhz_full(verbose, 2);
}
/** Special counters that compensate for timer interrupt overhead */
static double cyc_per_tick = 0.0;
#define NEVENT 100
#define THRESHOLD 1000
#define RECORDTHRESH 3000
/* Attempt to see how much time is used by timer interrupt */
static void callibrate(int verbose)
{
double oldt;
struct tms t;
clock_t oldc;
int e = 0;
times(&t);
oldc = t.tms_utime;
start_counter();
oldt = get_counter();
while (e <NEVENT) {
double newt = get_counter();
if (newt-oldt >= THRESHOLD) {
clock_t newc;
times(&t);
newc = t.tms_utime;
if (newc > oldc) {
double cpt = (newt-oldt)/(newc-oldc);
if ((cyc_per_tick == 0.0 || cyc_per_tick > cpt) && cpt > RECORDTHRESH)
cyc_per_tick = cpt;
/*
if (verbose)
printf("Saw event lasting %.0f cycles and %d ticks. Ratio = %f\n",
newt-oldt, (int) (newc-oldc), cpt);
*/
e++;
oldc = newc;
}
oldt = newt;
}
}
if (verbose)
printf("Setting cyc_per_tick to %f\n", cyc_per_tick);
}
static clock_t start_tick = 0;
void start_comp_counter()
{
struct tms t;
if (cyc_per_tick == 0.0)
callibrate(0);
times(&t);
start_tick = t.tms_utime;
start_counter();
}
double get_comp_counter()
{
double time = get_counter();
double ctime;
struct tms t;
clock_t ticks;
times(&t);
ticks = t.tms_utime - start_tick;
ctime = time - ticks*cyc_per_tick;
/*
printf("Measured %.0f cycles. Ticks = %d. Corrected %.0f cycles\n",
time, (int) ticks, ctime);
*/
return ctime;
}