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clock.c
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clock.c
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/*
* clock.c - Routines for using the cycle counters on x86,
* Alpha, and Sparc boxes.
*
* 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 <unistd.h>
#include <sys/times.h>
#include "clock.h"
/*******************************************************
* Machine dependent functions
*
* Note: the constants __i386__ and __alpha
* are set by GCC when it calls the C preprocessor
* You can verify this for yourself using gcc -v.
*******************************************************/
#if defined(__i386__)
/*******************************************************
* 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; movl %%edx,%0; movl %%eax,%1" /* Read cycle counter */
: "=r" (*hi), "=r" (*lo) /* and move results to */
: /* No input */ /* the two outputs */
: "%edx", "%eax");
}
/* 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 */
#elif defined(__alpha)
/****************************************************
* Alpha versions of start_counter() and get_counter()
***************************************************/
/* Initialize the cycle counter */
static unsigned cyc_hi = 0;
static unsigned cyc_lo = 0;
/* Use Alpha cycle timer to compute cycles. Then use
measured clock speed to compute seconds
*/
/*
* counterRoutine is an array of Alpha instructions to access
* the Alpha's processor cycle counter. It uses the rpcc
* instruction to access the counter. This 64 bit register is
* divided into two parts. The lower 32 bits are the cycles
* used by the current process. The upper 32 bits are wall
* clock cycles. These instructions read the counter, and
* convert the lower 32 bits into an unsigned int - this is the
* user space counter value.
* NOTE: The counter has a very limited time span. With a
* 450MhZ clock the counter can time things for about 9
* seconds. */
static unsigned int counterRoutine[] =
{
0x601fc000u,
0x401f0000u,
0x6bfa8001u
};
/* Cast the above instructions into a function. */
static unsigned int (*counter)(void)= (void *)counterRoutine;
void start_counter()
{
/* Get cycle counter */
cyc_hi = 0;
cyc_lo = counter();
}
double get_counter()
{
unsigned ncyc_hi, ncyc_lo;
unsigned hi, lo, borrow;
double result;
ncyc_lo = counter();
ncyc_hi = 0;
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: Cycle counter returning negative value: %.0f\n", result);
}
return result;
}
#else
/****************************************************************
* All the other platforms for which we haven't implemented cycle
* counter routines. Newer models of sparcs (v8plus) have cycle
* counters that can be accessed from user programs, but since there
* are still many sparc boxes out there that don't support this, we
* haven't provided a Sparc version here.
***************************************************************/
void start_counter()
{
printf("ERROR: You are trying to use a start_counter routine in clock.c\n");
printf("that has not been implemented yet on this platform.\n");
printf("Please choose another timing package in config.h.\n");
exit(1);
}
double get_counter()
{
printf("ERROR: You are trying to use a get_counter routine in clock.c\n");
printf("that has not been implemented yet on this platform.\n");
printf("Please choose another timing package in config.h.\n");
exit(1);
}
#endif
/*******************************
* Machine-independent functions
******************************/
double ovhd()
{
/* Do it twice to eliminate cache effects */
int i;
double result;
for (i = 0; i < 2; i++) {
start_counter();
result = get_counter();
}
return result;
}
/* $begin mhz */
/* Estimate the clock rate by measuring the cycles that elapse */
/* while sleeping for sleeptime seconds */
double mhz_full(int verbose, int sleeptime)
{
double rate;
start_counter();
sleep(sleeptime);
rate = get_counter() / (1e6*sleeptime);
if (verbose)
printf("Processor clock rate ~= %.1f MHz\n", rate);
return rate;
}
/* $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;
}