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279 righe
6.9 KiB
279 righe
6.9 KiB
/*
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* clock.c - Routines for using the cycle counters on x86,
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* Alpha, and Sparc boxes.
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*
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* Copyright (c) 2002, R. Bryant and D. O'Hallaron, All rights reserved.
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* May not be used, modified, or copied without permission.
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*/
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#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 "clock.h"
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/*******************************************************
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* Machine dependent functions
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*
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* Note: the constants __i386__ and __alpha
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* are set by GCC when it calls the C preprocessor
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* You can verify this for yourself using gcc -v.
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*******************************************************/
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#if defined(__i386__)
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/*******************************************************
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* Pentium versions of start_counter() and get_counter()
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*******************************************************/
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/* $begin x86cyclecounter */
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/* Initialize the cycle counter */
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static unsigned cyc_hi = 0;
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static unsigned cyc_lo = 0;
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/* Set *hi and *lo to the high and low order bits of the cycle counter.
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Implementation requires assembly code to use the rdtsc instruction. */
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void access_counter(unsigned *hi, unsigned *lo)
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{
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asm("rdtsc; movl %%edx,%0; movl %%eax,%1" /* Read cycle counter */
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: "=r" (*hi), "=r" (*lo) /* and move results to */
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: /* No input */ /* the two outputs */
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: "%edx", "%eax");
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}
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/* Record the current value of the cycle counter. */
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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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/* Return the number of cycles since the last call to start_counter. */
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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: counter returns neg value: %.0f\n", result);
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}
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return result;
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}
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/* $end x86cyclecounter */
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#elif defined(__alpha)
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/****************************************************
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* Alpha versions of start_counter() and get_counter()
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***************************************************/
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/* Initialize the cycle counter */
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static unsigned cyc_hi = 0;
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static unsigned cyc_lo = 0;
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/* Use Alpha cycle timer to compute cycles. Then use
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measured clock speed to compute seconds
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*/
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/*
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* counterRoutine is an array of Alpha instructions to access
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* the Alpha's processor cycle counter. It uses the rpcc
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* instruction to access the counter. This 64 bit register is
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* divided into two parts. The lower 32 bits are the cycles
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* used by the current process. The upper 32 bits are wall
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* clock cycles. These instructions read the counter, and
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* convert the lower 32 bits into an unsigned int - this is the
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* user space counter value.
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* NOTE: The counter has a very limited time span. With a
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* 450MhZ clock the counter can time things for about 9
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* seconds. */
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static unsigned int counterRoutine[] =
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{
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0x601fc000u,
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0x401f0000u,
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0x6bfa8001u
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};
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/* Cast the above instructions into a function. */
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static unsigned int (*counter)(void)= (void *)counterRoutine;
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void start_counter()
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{
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/* Get cycle counter */
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cyc_hi = 0;
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cyc_lo = counter();
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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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ncyc_lo = counter();
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ncyc_hi = 0;
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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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#else
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/****************************************************************
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* All the other platforms for which we haven't implemented cycle
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* counter routines. Newer models of sparcs (v8plus) have cycle
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* counters that can be accessed from user programs, but since there
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* are still many sparc boxes out there that don't support this, we
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* haven't provided a Sparc version here.
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***************************************************************/
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void start_counter()
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{
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printf("ERROR: You are trying to use a start_counter routine in clock.c\n");
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printf("that has not been implemented yet on this platform.\n");
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printf("Please choose another timing package in config.h.\n");
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exit(1);
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}
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double get_counter()
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{
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printf("ERROR: You are trying to use a get_counter routine in clock.c\n");
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printf("that has not been implemented yet on this platform.\n");
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printf("Please choose another timing package in config.h.\n");
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exit(1);
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}
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#endif
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/*******************************
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* Machine-independent functions
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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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/* $begin mhz */
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/* Estimate the clock rate by measuring the cycles that elapse */
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/* 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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/* $end mhz */
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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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{
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struct tms t;
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if (cyc_per_tick == 0.0)
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callibrate(0);
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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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{
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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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