1 /* $NetBSD: kern_microtime.c,v 1.4.4.2 2004/07/04 12:34:32 he Exp $ */
2
3 /*-
4 * Copyright (c) 2001 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. All advertising materials mentioning features or use of this software
19 * must display the following acknowledgement:
20 * This product includes software developed by the NetBSD
21 * Foundation, Inc. and its contributors.
22 * 4. Neither the name of The NetBSD Foundation nor the names of its
23 * contributors may be used to endorse or promote products derived
24 * from this software without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
36 * POSSIBILITY OF SUCH DAMAGE.
37 */
38
39 /******************************************************************************
40 * *
41 * Copyright (c) David L. Mills 1993, 1994 *
42 * *
43 * Permission to use, copy, modify, and distribute this software and its *
44 * documentation for any purpose and without fee is hereby granted, provided *
45 * that the above copyright notice appears in all copies and that both the *
46 * copyright notice and this permission notice appear in supporting *
47 * documentation, and that the name University of Delaware not be used in *
48 * advertising or publicity pertaining to distribution of the software *
49 * without specific, written prior permission. The University of Delaware *
50 * makes no representations about the suitability this software for any *
51 * purpose. It is provided "as is" without express or implied warranty. *
52 * *
53 ******************************************************************************/
54
55 #include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
56
57 __KERNEL_RCSID(0, "$NetBSD: kern_microtime.c,v 1.4.4.2 2004/07/04 12:34:32 he Exp $");
58
59 #include "opt_multiprocessor.h"
60
61 #include <sys/param.h>
62 #include <sys/systm.h>
63 #include <sys/kernel.h>
64 #include <sys/lock.h>
65
66 #include <machine/cpu.h>
67 #include <machine/cpu_counter.h>
68
69 struct timeval cc_microset_time;
70
71 /*
72 * Return the best possible estimate of the time in the timeval to which
73 * tvp points. The kernel logical time variable is interpolated between
74 * ticks by reading the CC to determine the number of cycles since the
75 * last processor update, then converting the result to microseconds. In
76 * the case of multiprocessor systems, the interpolation is specific to
77 * each processor, since each processor has its own CC.
78 */
79 void
80 cc_microtime(struct timeval *tvp)
81 {
82 static struct timeval lasttime;
83 static struct simplelock microtime_slock = SIMPLELOCK_INITIALIZER;
84 struct timeval t;
85 struct cpu_info *ci = curcpu();
86 int64_t cc, sec, usec;
87 int s;
88
89 #ifdef MULTIPROCESSOR
90 s = splipi(); /* also blocks IPIs */
91 #else
92 s = splclock(); /* block clock interrupts */
93 #endif
94
95 if (ci->ci_cc_denom != 0) {
96 /*
97 * Determine the current clock time as the time at last
98 * microset() call, plus the CC accumulation since then.
99 * This time should lie in the interval between the current
100 * master clock time and the time at the next tick, but
101 * this code does not explicitly require that in the interest
102 * of speed. If something ugly occurs, like a settimeofday()
103 * call, the processors may disagree among themselves for not
104 * more than the interval between microset() calls. In any
105 * case, the following sanity checks will suppress timewarps.
106 */
107 simple_lock(µtime_slock);
108 t = ci->ci_cc_time;
109 cc = cpu_counter32() - ci->ci_cc_cc;
110 if (cc < 0)
111 cc += 0x100000000LL;
112 t.tv_usec += (cc * ci->ci_cc_ms_delta) / ci->ci_cc_denom;
113 while (t.tv_usec >= 1000000) {
114 t.tv_usec -= 1000000;
115 t.tv_sec++;
116 }
117 } else {
118 /*
119 * Can't use the CC -- just use the system time.
120 */
121 /* XXXSMP: not atomic */
122 simple_lock(µtime_slock);
123 t = time;
124 }
125
126 /*
127 * Ordinarily, the current clock time is guaranteed to be later
128 * by at least one microsecond than the last time the clock was
129 * read. However, this rule applies only if the current time is
130 * within one second of the last time. Otherwise, the clock will
131 * (shudder) be set backward. The clock adjustment daemon or
132 * human equivalent is presumed to be correctly implemented and
133 * to set the clock backward only upon unavoidable crisis.
134 */
135 sec = lasttime.tv_sec - t.tv_sec;
136 usec = lasttime.tv_usec - t.tv_usec;
137 if (usec < 0) {
138 usec += 1000000;
139 sec--;
140 }
141 if (sec == 0 && usec > 0) {
142 t.tv_usec += usec + 1;
143 if (t.tv_usec >= 1000000) {
144 t.tv_usec -= 1000000;
145 t.tv_sec++;
146 }
147 }
148 lasttime = t;
149 simple_unlock(µtime_slock);
150
151 splx(s);
152
153 *tvp = t;
154 }
155
156 /*
157 * This routine is called about once per second directly by the master
158 * processor and via an interprocessor interrupt for other processors.
159 * It determines the CC frequency of each processor relative to the
160 * master clock and the time this determination is made. These values
161 * are used by microtime() to interpolate the microseconds between
162 * timer interrupts. Note that we assume the kernel variables have
163 * been zeroed early in life.
164 */
165 void
166 cc_microset(struct cpu_info *ci)
167 {
168 struct timeval t;
169 int64_t delta, denom;
170
171 /* Note: Clock interrupts are already blocked. */
172
173 denom = ci->ci_cc_cc;
174 t = cc_microset_time; /* XXXSMP: not atomic */
175 ci->ci_cc_cc = cpu_counter32();
176
177 if (ci->ci_cc_denom == 0) {
178 /*
179 * This is our first time here on this CPU. Just
180 * start with reasonable initial values.
181 */
182 ci->ci_cc_time = t;
183 ci->ci_cc_ms_delta = 1000000;
184 ci->ci_cc_denom = cpu_frequency(ci);
185 return;
186 }
187
188 denom = ci->ci_cc_cc - denom;
189 if (denom < 0)
190 denom += 0x100000000LL;
191
192 delta = (t.tv_sec - ci->ci_cc_time.tv_sec) * 1000000 +
193 (t.tv_usec - ci->ci_cc_time.tv_usec);
194
195 ci->ci_cc_time = t;
196 /*
197 * Make sure it's within .5 to 1.5 seconds -- otherwise,
198 * the time is probably be frobbed with by the timekeeper
199 * or the human.
200 */
201 if (delta > 500000 && delta < 1500000) {
202 ci->ci_cc_ms_delta = delta;
203 ci->ci_cc_denom = denom;
204 #if 0
205 printf("cc_microset: delta %" PRId64 ", denom %" PRId64 "\n",
206 delta, denom);
207 #endif
208 } else {
209 #if 0
210 printf("cc_microset: delta %" PRId64 ", resetting state\n",
211 delta);
212 #endif
213 ci->ci_cc_ms_delta = 1000000;
214 ci->ci_cc_denom = cpu_frequency(ci);
215 }
216 }
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