Monk’s Blog

#include <stdio.h>
#include <time.h>
#include <sys/time.h>
 
#define rdtsc(low) \
   __asm__ __volatile__("rdtsc" : "=a" (low) : : "edx")
 
#define TIME(x,y) \
        min = 100000;                                           \
        for (i = 0; i < 1000; i++) {                            \
                unsigned long start,end;                        \
                rdtsc(start);                                   \
                x;                                              \
                rdtsc(end);                                     \
                end -= start;                                   \
                if (end < min)                                  \
                        min = end;                              \
        }                                                       \
        printf(y ": %d cycles\n", min);
 
#define LOCK    asm volatile("lock ; addl $0,0(%esp)")
#define CPUID   asm volatile("cpuid": : :"ax", "dx", "cx", "bx")
#if 0
#define GTOD    gettimeofday (&tvstart, NULL); gettimeofday (&tvstop, NULL)
#endif
int main()
{
        struct timeval tvstart, tvstop;
        unsigned long min;
        int i;
 
#if 0
        TIME(GTOD, "gettimeofday start/stop:");
#endif
        TIME(/* */, "nothing:");
        TIME(LOCK, "locked add:");
        TIME(CPUID, "cpuid:");
}

#include <stdio.h>
#include <sys/time.h>
 
#define rdtsc(low) \
   __asm__ __volatile__("rdtsc" : "=a" (low) : : "edx")
 
#define TIME(x,y) \
        min = 100000;                                           \
        for (i = 0; i < 1000; i++) {                            \
                unsigned long start,end;                        \
                rdtsc(start);                                   \
                x;                                              \
                rdtsc(end);                                     \
                end -= start;                                   \
                if (end < min)                                  \
                        min = end;                              \
        }                                                       \
        printf(y ": %d cycles\n", min);
 
#define LOCK    asm volatile("lock ; addl $0,0(%esp)")
#define CPUID   asm volatile("cpuid": : :"ax", "dx", "cx", "bx")
#define GTOD1   gettimeofday(&one, NULL)
#define GTOD2   gettimeofday(&one, NULL); gettimeofday(&two, NULL) 
 
int main()
{
        unsigned long min;
        int i;
        struct timeval one, two;
 
        TIME(/* */, "nothing");
        TIME(LOCK, "locked add");
        TIME(CPUID, "cpuid");
        TIME(GTOD1, "gettimeofday");
        TIME(GTOD2, "gettimeofday start/stop");
}

/*-
 * Copyright (c) 2007 Gary Stanley <gary@velocity-servers.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */
 
 
#include <time.h>
#include <stdio.h>
#include <sys/time.h>
 
/*
 * This measures latency of gettimeofday and clock_gettime
 * With TSC i get the best results, AMD and Intel
 * I get the worst results with 8254 and ACPI-{fast,slow}
 * HPET is around 1200 cycles, which almost as slow as ACPI
 */
 
int
main(void) {
        int i, tvusecs, tsusecs;
        struct timeval tvstart, tvstop;
        struct timespec tsstart, tsstop;
 
        gettimeofday (&tvstart, NULL);
        for (i = 0; i < 1000; i++)
                gettimeofday (&tvstop, NULL);
 
        clock_gettime (CLOCK_REALTIME, &tsstart);
        for (i = 0; i < 1000; i++)
        clock_gettime (CLOCK_REALTIME, &tsstop);
 
        tvusecs = ((tvstop.tv_sec - tvstart.tv_sec) * 1000000) + (tvstop.tv_usec - tvstart.tv_usec);
        tsusecs = ((tsstop.tv_sec - tsstart.tv_sec) * 1000000) + ((tsstop.tv_nsec - tsstart.tv_nsec) / 1000);
 
        printf ("1000 gettimeofday()'s = %d usecs; ~ %d usecs each\n", tvusecs, tvusecs / 1000);
        printf ("1000 clock_gettime()'s = %d usecs; ~ %d usecs each\n", tsusecs, tsusecs / 1000);
 
        return 0;
}