The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * Copyright (c) 1998-2003 Poul-Henning Kamp
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: releng/6.0/sys/i386/i386/tsc.c 121307 2003-10-21 18:28:36Z silby $");
   29 
   30 #include "opt_clock.h"
   31 
   32 #include <sys/param.h>
   33 #include <sys/systm.h>
   34 #include <sys/sysctl.h>
   35 #include <sys/time.h>
   36 #include <sys/timetc.h>
   37 #include <sys/kernel.h>
   38 #include <sys/power.h>
   39 #include <sys/smp.h>
   40 #include <machine/clock.h>
   41 #include <machine/md_var.h>
   42 #include <machine/specialreg.h>
   43 
   44 uint64_t        tsc_freq;
   45 int             tsc_is_broken;
   46 u_int           tsc_present;
   47 
   48 #ifdef SMP
   49 static int      smp_tsc;
   50 SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
   51     "Indicates whether the TSC is safe to use in SMP mode");
   52 TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);
   53 #endif
   54 
   55 static  unsigned tsc_get_timecount(struct timecounter *tc);
   56 
   57 static struct timecounter tsc_timecounter = {
   58         tsc_get_timecount,      /* get_timecount */
   59         0,                      /* no poll_pps */
   60         ~0u,                    /* counter_mask */
   61         0,                      /* frequency */
   62          "TSC",                 /* name */
   63         800,                    /* quality (adjusted in code) */
   64 };
   65 
   66 void
   67 init_TSC(void)
   68 {
   69         u_int64_t tscval[2];
   70 
   71         if (cpu_feature & CPUID_TSC)
   72                 tsc_present = 1;
   73         else
   74                 tsc_present = 0;
   75 
   76         if (!tsc_present) 
   77                 return;
   78 
   79         if (bootverbose)
   80                 printf("Calibrating TSC clock ... ");
   81 
   82         tscval[0] = rdtsc();
   83         DELAY(1000000);
   84         tscval[1] = rdtsc();
   85 
   86         tsc_freq = tscval[1] - tscval[0];
   87         if (bootverbose)
   88                 printf("TSC clock: %ju Hz\n", (intmax_t)tsc_freq);
   89 }
   90 
   91 
   92 void
   93 init_TSC_tc(void)
   94 {
   95         /*
   96          * We can not use the TSC if we support APM. Precise timekeeping
   97          * on an APM'ed machine is at best a fools pursuit, since 
   98          * any and all of the time spent in various SMM code can't 
   99          * be reliably accounted for.  Reading the RTC is your only
  100          * source of reliable time info.  The i8254 looses too of course
  101          * but we need to have some kind of time...
  102          * We don't know at this point whether APM is going to be used
  103          * or not, nor when it might be activated.  Play it safe.
  104          */
  105         if (power_pm_get_type() == POWER_PM_TYPE_APM) {
  106                 tsc_timecounter.tc_quality = -1000;
  107                 if (bootverbose)
  108                         printf("TSC timecounter disabled: APM enabled.\n");
  109         }
  110 
  111 #ifdef SMP
  112         /*
  113          * We can not use the TSC in SMP mode unless the TSCs on all CPUs
  114          * are somehow synchronized.  Some hardware configurations do
  115          * this, but we have no way of determining whether this is the
  116          * case, so we do not use the TSC in multi-processor systems
  117          * unless the user indicated (by setting kern.timecounter.smp_tsc
  118          * to 1) that he believes that his TSCs are synchronized.
  119          */
  120         if (mp_ncpus > 1 && !smp_tsc)
  121                 tsc_timecounter.tc_quality = -100;
  122 #endif
  123 
  124         if (tsc_present && tsc_freq != 0 && !tsc_is_broken) {
  125                 tsc_timecounter.tc_frequency = tsc_freq;
  126                 tc_init(&tsc_timecounter);
  127         }
  128 }
  129 
  130 static int
  131 sysctl_machdep_tsc_freq(SYSCTL_HANDLER_ARGS)
  132 {
  133         int error;
  134         uint64_t freq;
  135 
  136         if (tsc_timecounter.tc_frequency == 0)
  137                 return (EOPNOTSUPP);
  138         freq = tsc_freq;
  139         error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
  140         if (error == 0 && req->newptr != NULL) {
  141                 tsc_freq = freq;
  142                 tsc_timecounter.tc_frequency = tsc_freq;
  143         }
  144         return (error);
  145 }
  146 
  147 SYSCTL_PROC(_machdep, OID_AUTO, tsc_freq, CTLTYPE_QUAD | CTLFLAG_RW,
  148     0, sizeof(u_int), sysctl_machdep_tsc_freq, "IU", "");
  149 
  150 static unsigned
  151 tsc_get_timecount(struct timecounter *tc)
  152 {
  153         return (rdtsc());
  154 }

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