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