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1/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7#include <linux/jiffies.h>
8#include <linux/delay.h>
9#include <linux/init.h>
10#include <linux/timex.h>
11#include <linux/smp.h>
12#include <linux/percpu.h>
13
14unsigned long lpj_fine;
15unsigned long preset_lpj;
16static int __init lpj_setup(char *str)
17{
18 preset_lpj = simple_strtoul(str,NULL,0);
19 return 1;
20}
21
22__setup("lpj=", lpj_setup);
23
24#ifdef ARCH_HAS_READ_CURRENT_TIMER
25
26/* This routine uses the read_current_timer() routine and gets the
27 * loops per jiffy directly, instead of guessing it using delay().
28 * Also, this code tries to handle non-maskable asynchronous events
29 * (like SMIs)
30 */
31#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
32#define MAX_DIRECT_CALIBRATION_RETRIES 5
33
34static unsigned long calibrate_delay_direct(void)
35{
36 unsigned long pre_start, start, post_start;
37 unsigned long pre_end, end, post_end;
38 unsigned long start_jiffies;
39 unsigned long timer_rate_min, timer_rate_max;
40 unsigned long good_timer_sum = 0;
41 unsigned long good_timer_count = 0;
42 unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
43 int max = -1; /* index of measured_times with max/min values or not set */
44 int min = -1;
45 int i;
46
47 if (read_current_timer(&pre_start) < 0 )
48 return 0;
49
50 /*
51 * A simple loop like
52 * while ( jiffies < start_jiffies+1)
53 * start = read_current_timer();
54 * will not do. As we don't really know whether jiffy switch
55 * happened first or timer_value was read first. And some asynchronous
56 * event can happen between these two events introducing errors in lpj.
57 *
58 * So, we do
59 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
60 * 2. check jiffy switch
61 * 3. start <- timer value before or after jiffy switch
62 * 4. post_start <- When we are sure that jiffy switch has happened
63 *
64 * Note, we don't know anything about order of 2 and 3.
65 * Now, by looking at post_start and pre_start difference, we can
66 * check whether any asynchronous event happened or not
67 */
68
69 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
70 pre_start = 0;
71 read_current_timer(&start);
72 start_jiffies = jiffies;
73 while (time_before_eq(jiffies, start_jiffies + 1)) {
74 pre_start = start;
75 read_current_timer(&start);
76 }
77 read_current_timer(&post_start);
78
79 pre_end = 0;
80 end = post_start;
81 while (time_before_eq(jiffies, start_jiffies + 1 +
82 DELAY_CALIBRATION_TICKS)) {
83 pre_end = end;
84 read_current_timer(&end);
85 }
86 read_current_timer(&post_end);
87
88 timer_rate_max = (post_end - pre_start) /
89 DELAY_CALIBRATION_TICKS;
90 timer_rate_min = (pre_end - post_start) /
91 DELAY_CALIBRATION_TICKS;
92
93 /*
94 * If the upper limit and lower limit of the timer_rate is
95 * >= 12.5% apart, redo calibration.
96 */
97 if (start >= post_end)
98 printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
99 "timer_rate as we had a TSC wrap around"
100 " start=%lu >=post_end=%lu\n",
101 start, post_end);
102 if (start < post_end && pre_start != 0 && pre_end != 0 &&
103 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
104 good_timer_count++;
105 good_timer_sum += timer_rate_max;
106 measured_times[i] = timer_rate_max;
107 if (max < 0 || timer_rate_max > measured_times[max])
108 max = i;
109 if (min < 0 || timer_rate_max < measured_times[min])
110 min = i;
111 } else
112 measured_times[i] = 0;
113
114 }
115
116 /*
117 * Find the maximum & minimum - if they differ too much throw out the
118 * one with the largest difference from the mean and try again...
119 */
120 while (good_timer_count > 1) {
121 unsigned long estimate;
122 unsigned long maxdiff;
123
124 /* compute the estimate */
125 estimate = (good_timer_sum/good_timer_count);
126 maxdiff = estimate >> 3;
127
128 /* if range is within 12% let's take it */
129 if ((measured_times[max] - measured_times[min]) < maxdiff)
130 return estimate;
131
132 /* ok - drop the worse value and try again... */
133 good_timer_sum = 0;
134 good_timer_count = 0;
135 if ((measured_times[max] - estimate) <
136 (estimate - measured_times[min])) {
137 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
138 "min bogoMips estimate %d = %lu\n",
139 min, measured_times[min]);
140 measured_times[min] = 0;
141 min = max;
142 } else {
143 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
144 "max bogoMips estimate %d = %lu\n",
145 max, measured_times[max]);
146 measured_times[max] = 0;
147 max = min;
148 }
149
150 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
151 if (measured_times[i] == 0)
152 continue;
153 good_timer_count++;
154 good_timer_sum += measured_times[i];
155 if (measured_times[i] < measured_times[min])
156 min = i;
157 if (measured_times[i] > measured_times[max])
158 max = i;
159 }
160
161 }
162
163 printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
164 "estimate for loops_per_jiffy.\nProbably due to long platform "
165 "interrupts. Consider using \"lpj=\" boot option.\n");
166 return 0;
167}
168#else
169static unsigned long calibrate_delay_direct(void)
170{
171 return 0;
172}
173#endif
174
175/*
176 * This is the number of bits of precision for the loops_per_jiffy. Each
177 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
178 * to start with a good estimate.
179 * For the boot cpu we can skip the delay calibration and assign it a value
180 * calculated based on the timer frequency.
181 * For the rest of the CPUs we cannot assume that the timer frequency is same as
182 * the cpu frequency, hence do the calibration for those.
183 */
184#define LPS_PREC 8
185
186static unsigned long calibrate_delay_converge(void)
187{
188 /* First stage - slowly accelerate to find initial bounds */
189 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
190 int trials = 0, band = 0, trial_in_band = 0;
191
192 lpj = (1<<12);
193
194 /* wait for "start of" clock tick */
195 ticks = jiffies;
196 while (ticks == jiffies)
197 ; /* nothing */
198 /* Go .. */
199 ticks = jiffies;
200 do {
201 if (++trial_in_band == (1<<band)) {
202 ++band;
203 trial_in_band = 0;
204 }
205 __delay(lpj * band);
206 trials += band;
207 } while (ticks == jiffies);
208 /*
209 * We overshot, so retreat to a clear underestimate. Then estimate
210 * the largest likely undershoot. This defines our chop bounds.
211 */
212 trials -= band;
213 loopadd_base = lpj * band;
214 lpj_base = lpj * trials;
215
216recalibrate:
217 lpj = lpj_base;
218 loopadd = loopadd_base;
219
220 /*
221 * Do a binary approximation to get lpj set to
222 * equal one clock (up to LPS_PREC bits)
223 */
224 chop_limit = lpj >> LPS_PREC;
225 while (loopadd > chop_limit) {
226 lpj += loopadd;
227 ticks = jiffies;
228 while (ticks == jiffies)
229 ; /* nothing */
230 ticks = jiffies;
231 __delay(lpj);
232 if (jiffies != ticks) /* longer than 1 tick */
233 lpj -= loopadd;
234 loopadd >>= 1;
235 }
236 /*
237 * If we incremented every single time possible, presume we've
238 * massively underestimated initially, and retry with a higher
239 * start, and larger range. (Only seen on x86_64, due to SMIs)
240 */
241 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
242 lpj_base = lpj;
243 loopadd_base <<= 2;
244 goto recalibrate;
245 }
246
247 return lpj;
248}
249
250static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
251
252/*
253 * Check if cpu calibration delay is already known. For example,
254 * some processors with multi-core sockets may have all cores
255 * with the same calibration delay.
256 *
257 * Architectures should override this function if a faster calibration
258 * method is available.
259 */
260unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
261{
262 return 0;
263}
264
265/*
266 * Indicate the cpu delay calibration is done. This can be used by
267 * architectures to stop accepting delay timer registrations after this point.
268 */
269
270void __attribute__((weak)) calibration_delay_done(void)
271{
272}
273
274void calibrate_delay(void)
275{
276 unsigned long lpj;
277 static bool printed;
278 int this_cpu = smp_processor_id();
279
280 if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
281 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
282 if (!printed)
283 pr_info("Calibrating delay loop (skipped) "
284 "already calibrated this CPU");
285 } else if (preset_lpj) {
286 lpj = preset_lpj;
287 if (!printed)
288 pr_info("Calibrating delay loop (skipped) "
289 "preset value.. ");
290 } else if ((!printed) && lpj_fine) {
291 lpj = lpj_fine;
292 pr_info("Calibrating delay loop (skipped), "
293 "value calculated using timer frequency.. ");
294 } else if ((lpj = calibrate_delay_is_known())) {
295 ;
296 } else if ((lpj = calibrate_delay_direct()) != 0) {
297 if (!printed)
298 pr_info("Calibrating delay using timer "
299 "specific routine.. ");
300 } else {
301 if (!printed)
302 pr_info("Calibrating delay loop... ");
303 lpj = calibrate_delay_converge();
304 }
305 per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
306 if (!printed)
307 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
308 lpj/(500000/HZ),
309 (lpj/(5000/HZ)) % 100, lpj);
310
311 loops_per_jiffy = lpj;
312 printed = true;
313
314 calibration_delay_done();
315}
1// SPDX-License-Identifier: GPL-2.0
2/* calibrate.c: default delay calibration
3 *
4 * Excised from init/main.c
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 */
7
8#include <linux/jiffies.h>
9#include <linux/delay.h>
10#include <linux/init.h>
11#include <linux/timex.h>
12#include <linux/smp.h>
13#include <linux/percpu.h>
14
15unsigned long lpj_fine;
16unsigned long preset_lpj;
17static int __init lpj_setup(char *str)
18{
19 preset_lpj = simple_strtoul(str,NULL,0);
20 return 1;
21}
22
23__setup("lpj=", lpj_setup);
24
25#ifdef ARCH_HAS_READ_CURRENT_TIMER
26
27/* This routine uses the read_current_timer() routine and gets the
28 * loops per jiffy directly, instead of guessing it using delay().
29 * Also, this code tries to handle non-maskable asynchronous events
30 * (like SMIs)
31 */
32#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
33#define MAX_DIRECT_CALIBRATION_RETRIES 5
34
35static unsigned long calibrate_delay_direct(void)
36{
37 unsigned long pre_start, start, post_start;
38 unsigned long pre_end, end, post_end;
39 unsigned long start_jiffies;
40 unsigned long timer_rate_min, timer_rate_max;
41 unsigned long good_timer_sum = 0;
42 unsigned long good_timer_count = 0;
43 unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
44 int max = -1; /* index of measured_times with max/min values or not set */
45 int min = -1;
46 int i;
47
48 if (read_current_timer(&pre_start) < 0 )
49 return 0;
50
51 /*
52 * A simple loop like
53 * while ( jiffies < start_jiffies+1)
54 * start = read_current_timer();
55 * will not do. As we don't really know whether jiffy switch
56 * happened first or timer_value was read first. And some asynchronous
57 * event can happen between these two events introducing errors in lpj.
58 *
59 * So, we do
60 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
61 * 2. check jiffy switch
62 * 3. start <- timer value before or after jiffy switch
63 * 4. post_start <- When we are sure that jiffy switch has happened
64 *
65 * Note, we don't know anything about order of 2 and 3.
66 * Now, by looking at post_start and pre_start difference, we can
67 * check whether any asynchronous event happened or not
68 */
69
70 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
71 pre_start = 0;
72 read_current_timer(&start);
73 start_jiffies = jiffies;
74 while (time_before_eq(jiffies, start_jiffies + 1)) {
75 pre_start = start;
76 read_current_timer(&start);
77 }
78 read_current_timer(&post_start);
79
80 pre_end = 0;
81 end = post_start;
82 while (time_before_eq(jiffies, start_jiffies + 1 +
83 DELAY_CALIBRATION_TICKS)) {
84 pre_end = end;
85 read_current_timer(&end);
86 }
87 read_current_timer(&post_end);
88
89 timer_rate_max = (post_end - pre_start) /
90 DELAY_CALIBRATION_TICKS;
91 timer_rate_min = (pre_end - post_start) /
92 DELAY_CALIBRATION_TICKS;
93
94 /*
95 * If the upper limit and lower limit of the timer_rate is
96 * >= 12.5% apart, redo calibration.
97 */
98 if (start >= post_end)
99 printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
100 "timer_rate as we had a TSC wrap around"
101 " start=%lu >=post_end=%lu\n",
102 start, post_end);
103 if (start < post_end && pre_start != 0 && pre_end != 0 &&
104 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
105 good_timer_count++;
106 good_timer_sum += timer_rate_max;
107 measured_times[i] = timer_rate_max;
108 if (max < 0 || timer_rate_max > measured_times[max])
109 max = i;
110 if (min < 0 || timer_rate_max < measured_times[min])
111 min = i;
112 } else
113 measured_times[i] = 0;
114
115 }
116
117 /*
118 * Find the maximum & minimum - if they differ too much throw out the
119 * one with the largest difference from the mean and try again...
120 */
121 while (good_timer_count > 1) {
122 unsigned long estimate;
123 unsigned long maxdiff;
124
125 /* compute the estimate */
126 estimate = (good_timer_sum/good_timer_count);
127 maxdiff = estimate >> 3;
128
129 /* if range is within 12% let's take it */
130 if ((measured_times[max] - measured_times[min]) < maxdiff)
131 return estimate;
132
133 /* ok - drop the worse value and try again... */
134 good_timer_sum = 0;
135 good_timer_count = 0;
136 if ((measured_times[max] - estimate) <
137 (estimate - measured_times[min])) {
138 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
139 "min bogoMips estimate %d = %lu\n",
140 min, measured_times[min]);
141 measured_times[min] = 0;
142 min = max;
143 } else {
144 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
145 "max bogoMips estimate %d = %lu\n",
146 max, measured_times[max]);
147 measured_times[max] = 0;
148 max = min;
149 }
150
151 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
152 if (measured_times[i] == 0)
153 continue;
154 good_timer_count++;
155 good_timer_sum += measured_times[i];
156 if (measured_times[i] < measured_times[min])
157 min = i;
158 if (measured_times[i] > measured_times[max])
159 max = i;
160 }
161
162 }
163
164 printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
165 "estimate for loops_per_jiffy.\nProbably due to long platform "
166 "interrupts. Consider using \"lpj=\" boot option.\n");
167 return 0;
168}
169#else
170static unsigned long calibrate_delay_direct(void)
171{
172 return 0;
173}
174#endif
175
176/*
177 * This is the number of bits of precision for the loops_per_jiffy. Each
178 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
179 * to start with a good estimate.
180 * For the boot cpu we can skip the delay calibration and assign it a value
181 * calculated based on the timer frequency.
182 * For the rest of the CPUs we cannot assume that the timer frequency is same as
183 * the cpu frequency, hence do the calibration for those.
184 */
185#define LPS_PREC 8
186
187static unsigned long calibrate_delay_converge(void)
188{
189 /* First stage - slowly accelerate to find initial bounds */
190 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
191 int trials = 0, band = 0, trial_in_band = 0;
192
193 lpj = (1<<12);
194
195 /* wait for "start of" clock tick */
196 ticks = jiffies;
197 while (ticks == jiffies)
198 ; /* nothing */
199 /* Go .. */
200 ticks = jiffies;
201 do {
202 if (++trial_in_band == (1<<band)) {
203 ++band;
204 trial_in_band = 0;
205 }
206 __delay(lpj * band);
207 trials += band;
208 } while (ticks == jiffies);
209 /*
210 * We overshot, so retreat to a clear underestimate. Then estimate
211 * the largest likely undershoot. This defines our chop bounds.
212 */
213 trials -= band;
214 loopadd_base = lpj * band;
215 lpj_base = lpj * trials;
216
217recalibrate:
218 lpj = lpj_base;
219 loopadd = loopadd_base;
220
221 /*
222 * Do a binary approximation to get lpj set to
223 * equal one clock (up to LPS_PREC bits)
224 */
225 chop_limit = lpj >> LPS_PREC;
226 while (loopadd > chop_limit) {
227 lpj += loopadd;
228 ticks = jiffies;
229 while (ticks == jiffies)
230 ; /* nothing */
231 ticks = jiffies;
232 __delay(lpj);
233 if (jiffies != ticks) /* longer than 1 tick */
234 lpj -= loopadd;
235 loopadd >>= 1;
236 }
237 /*
238 * If we incremented every single time possible, presume we've
239 * massively underestimated initially, and retry with a higher
240 * start, and larger range. (Only seen on x86_64, due to SMIs)
241 */
242 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
243 lpj_base = lpj;
244 loopadd_base <<= 2;
245 goto recalibrate;
246 }
247
248 return lpj;
249}
250
251static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
252
253/*
254 * Check if cpu calibration delay is already known. For example,
255 * some processors with multi-core sockets may have all cores
256 * with the same calibration delay.
257 *
258 * Architectures should override this function if a faster calibration
259 * method is available.
260 */
261unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
262{
263 return 0;
264}
265
266/*
267 * Indicate the cpu delay calibration is done. This can be used by
268 * architectures to stop accepting delay timer registrations after this point.
269 */
270
271void __attribute__((weak)) calibration_delay_done(void)
272{
273}
274
275void calibrate_delay(void)
276{
277 unsigned long lpj;
278 static bool printed;
279 int this_cpu = smp_processor_id();
280
281 if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
282 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
283 if (!printed)
284 pr_info("Calibrating delay loop (skipped) "
285 "already calibrated this CPU");
286 } else if (preset_lpj) {
287 lpj = preset_lpj;
288 if (!printed)
289 pr_info("Calibrating delay loop (skipped) "
290 "preset value.. ");
291 } else if ((!printed) && lpj_fine) {
292 lpj = lpj_fine;
293 pr_info("Calibrating delay loop (skipped), "
294 "value calculated using timer frequency.. ");
295 } else if ((lpj = calibrate_delay_is_known())) {
296 ;
297 } else if ((lpj = calibrate_delay_direct()) != 0) {
298 if (!printed)
299 pr_info("Calibrating delay using timer "
300 "specific routine.. ");
301 } else {
302 if (!printed)
303 pr_info("Calibrating delay loop... ");
304 lpj = calibrate_delay_converge();
305 }
306 per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
307 if (!printed)
308 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
309 lpj/(500000/HZ),
310 (lpj/(5000/HZ)) % 100, lpj);
311
312 loops_per_jiffy = lpj;
313 printed = true;
314
315 calibration_delay_done();
316}