FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/tsc.c

     /*-
      * Copyright (c) 1998-2003 Poul-Henning Kamp
      * 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.
     *
     * $FreeBSD: releng/5.1/sys/i386/i386/tsc.c 113348 2003-04-10 23:07:24Z des $
     */
    
    #include "opt_clock.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/sysctl.h>
    #include <sys/time.h>
    #include <sys/timetc.h>
    #include <sys/kernel.h>
    #include <sys/power.h>
    #include <sys/smp.h>
    #include <machine/clock.h>
    #include <machine/md_var.h>
    #include <machine/specialreg.h>
    
    uint64_t        tsc_freq;
    int             tsc_is_broken;
    u_int           tsc_present;
    
    #ifdef SMP
    static int      smp_tsc;
    SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RD, &smp_tsc, 0,
        "Indicates whether the TSC is safe to use in SMP mode");
    TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);
    #endif
    
    static  unsigned tsc_get_timecount(struct timecounter *tc);
    
    static struct timecounter tsc_timecounter = {
            tsc_get_timecount,      /* get_timecount */
            0,                      /* no poll_pps */
            ~0u,                    /* counter_mask */
            0,                      /* frequency */
             "TSC"                  /* name */
    };
    
    void
    init_TSC(void)
    {
            u_int64_t tscval[2];
    
            if (cpu_feature & CPUID_TSC)
                    tsc_present = 1;
            else
                    tsc_present = 0;
    
            if (!tsc_present) 
                    return;
    
            if (bootverbose)
                    printf("Calibrating TSC clock ... ");
    
            tscval[0] = rdtsc();
            DELAY(1000000);
            tscval[1] = rdtsc();
    
            tsc_freq = tscval[1] - tscval[0];
            if (bootverbose)
                    printf("TSC clock: %ju Hz\n", (intmax_t)tsc_freq);
    
    #ifdef SMP
            /*
             * We can not use the TSC in SMP mode unless the TSCs on all CPUs
             * are somehow synchronized.  Some hardware configurations do
             * this, but we have no way of determining whether this is the
             * case, so we do not use the TSC in multi-processor systems
             * unless the user indicated (by setting kern.timecounter.smp_tsc
             * to 1) that he believes that his TSCs are synchronized.
             */
            if (mp_ncpus > 1 && !smp_tsc)
                    return;
    #endif
   
           /*
            * We can not use the TSC if we support APM. Precise timekeeping
            * on an APM'ed machine is at best a fools pursuit, since 
            * any and all of the time spent in various SMM code can't 
            * be reliably accounted for.  Reading the RTC is your only
            * source of reliable time info.  The i8254 looses too of course
            * but we need to have some kind of time...
            * We don't know at this point whether APM is going to be used
            * or not, nor when it might be activated.  Play it safe.
            */
           if (power_pm_get_type() == POWER_PM_TYPE_APM) {
                   if (bootverbose)
                           printf("TSC timecounter disabled: APM enabled.\n");
                   return;
           }
   
           if (tsc_present && tsc_freq != 0 && !tsc_is_broken) {
                   tsc_timecounter.tc_frequency = tsc_freq;
                   tc_init(&tsc_timecounter);
           }
   
           return;
   }
   
   static int
   sysctl_machdep_tsc_freq(SYSCTL_HANDLER_ARGS)
   {
           int error;
           uint64_t freq;
   
           if (tsc_timecounter.tc_frequency == 0)
                   return (EOPNOTSUPP);
           freq = tsc_freq;
           error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
           if (error == 0 && req->newptr != NULL) {
                   tsc_freq = freq;
                   tsc_timecounter.tc_frequency = tsc_freq;
           }
           return (error);
   }
   
   SYSCTL_PROC(_machdep, OID_AUTO, tsc_freq, CTLTYPE_QUAD | CTLFLAG_RW,
       0, sizeof(u_int), sysctl_machdep_tsc_freq, "IU", "");
   
   static unsigned
   tsc_get_timecount(struct timecounter *tc)
   {
           return (rdtsc());
   }

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