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/amd64/amd64/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/6.3/sys/amd64/amd64/tsc.c 173886 2007-11-24 19:45:58Z cvs2svn $");
   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 
   47 #ifdef SMP
   48 static int      smp_tsc;
   49 SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
   50     "Indicates whether the TSC is safe to use in SMP mode");
   51 TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);
   52 #endif
   53 
   54 static  unsigned tsc_get_timecount(struct timecounter *tc);
   55 
   56 static struct timecounter tsc_timecounter = {
   57         tsc_get_timecount,      /* get_timecount */
   58         0,                      /* no poll_pps */
   59         ~0u,                    /* counter_mask */
   60         0,                      /* frequency */
   61          "TSC",                 /* name */
   62         800,                    /* quality (adjusted in code) */
   63 };
   64 
   65 void
   66 init_TSC(void)
   67 {
   68         u_int64_t tscval[2];
   69 
   70         if (bootverbose)
   71                 printf("Calibrating TSC clock ... ");
   72 
   73         tscval[0] = rdtsc();
   74         DELAY(1000000);
   75         tscval[1] = rdtsc();
   76 
   77         tsc_freq = tscval[1] - tscval[0];
   78         if (bootverbose)
   79                 printf("TSC clock: %lu Hz\n", tsc_freq);
   80 }
   81 
   82 
   83 void
   84 init_TSC_tc(void)
   85 {
   86 
   87 #ifdef SMP
   88         /*
   89          * We can not use the TSC in SMP mode unless the TSCs on all CPUs
   90          * are somehow synchronized.  Some hardware configurations do
   91          * this, but we have no way of determining whether this is the
   92          * case, so we do not use the TSC in multi-processor systems
   93          * unless the user indicated (by setting kern.timecounter.smp_tsc
   94          * to 1) that he believes that his TSCs are synchronized.
   95          */
   96         if (mp_ncpus > 1 && !smp_tsc)
   97                 tsc_timecounter.tc_quality = -100;
   98 #endif
   99 
  100         if (tsc_freq != 0 && !tsc_is_broken) {
  101                 tsc_timecounter.tc_frequency = tsc_freq;
  102                 tc_init(&tsc_timecounter);
  103         }
  104 }
  105 
  106 static int
  107 sysctl_machdep_tsc_freq(SYSCTL_HANDLER_ARGS)
  108 {
  109         int error;
  110         uint64_t freq;
  111 
  112         if (tsc_timecounter.tc_frequency == 0)
  113                 return (EOPNOTSUPP);
  114         freq = tsc_freq;
  115         error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
  116         if (error == 0 && req->newptr != NULL) {
  117                 tsc_freq = freq;
  118                 tsc_timecounter.tc_frequency = tsc_freq;
  119         }
  120         return (error);
  121 }
  122 
  123 SYSCTL_PROC(_machdep, OID_AUTO, tsc_freq, CTLTYPE_LONG | CTLFLAG_RW,
  124     0, sizeof(u_int), sysctl_machdep_tsc_freq, "IU", "");
  125 
  126 static unsigned
  127 tsc_get_timecount(struct timecounter *tc)
  128 {
  129         return (rdtsc());
  130 }

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