Branch data Line data Source code
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 : :
15 : : unsigned long lpj_fine;
16 : : unsigned long preset_lpj;
17 : 0 : static int __init lpj_setup(char *str)
18 : : {
19 : 0 : preset_lpj = simple_strtoul(str,NULL,0);
20 : 0 : 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 : :
35 : 0 : static unsigned long calibrate_delay_direct(void)
36 : : {
37 : 0 : unsigned long pre_start, start, post_start;
38 : 0 : unsigned long pre_end, end, post_end;
39 : 0 : unsigned long start_jiffies;
40 : 0 : unsigned long timer_rate_min, timer_rate_max;
41 : 0 : unsigned long good_timer_sum = 0;
42 : 0 : unsigned long good_timer_count = 0;
43 : 0 : unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
44 : 0 : int max = -1; /* index of measured_times with max/min values or not set */
45 : 0 : int min = -1;
46 : 0 : int i;
47 : :
48 [ # # ]: 0 : 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 [ # # ]: 0 : for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
71 : 0 : pre_start = 0;
72 : 0 : read_current_timer(&start);
73 : 0 : start_jiffies = jiffies;
74 [ # # ]: 0 : while (time_before_eq(jiffies, start_jiffies + 1)) {
75 : 0 : pre_start = start;
76 : 0 : read_current_timer(&start);
77 : : }
78 : 0 : read_current_timer(&post_start);
79 : :
80 : 0 : pre_end = 0;
81 : 0 : end = post_start;
82 [ # # ]: 0 : while (time_before_eq(jiffies, start_jiffies + 1 +
83 : : DELAY_CALIBRATION_TICKS)) {
84 : 0 : pre_end = end;
85 : 0 : read_current_timer(&end);
86 : : }
87 : 0 : read_current_timer(&post_end);
88 : :
89 : 0 : timer_rate_max = (post_end - pre_start) /
90 : : DELAY_CALIBRATION_TICKS;
91 : 0 : 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 [ # # ]: 0 : if (start >= post_end)
99 : 0 : 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 [ # # # # : 0 : if (start < post_end && pre_start != 0 && pre_end != 0 &&
# # ]
104 [ # # ]: 0 : (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
105 : 0 : good_timer_count++;
106 : 0 : good_timer_sum += timer_rate_max;
107 : 0 : measured_times[i] = timer_rate_max;
108 [ # # # # ]: 0 : if (max < 0 || timer_rate_max > measured_times[max])
109 : 0 : max = i;
110 [ # # # # ]: 0 : if (min < 0 || timer_rate_max < measured_times[min])
111 : 0 : min = i;
112 : : } else
113 : 0 : 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 [ # # ]: 0 : while (good_timer_count > 1) {
122 : 0 : unsigned long estimate;
123 : 0 : unsigned long maxdiff;
124 : :
125 : : /* compute the estimate */
126 : 0 : estimate = (good_timer_sum/good_timer_count);
127 : 0 : maxdiff = estimate >> 3;
128 : :
129 : : /* if range is within 12% let's take it */
130 [ # # ]: 0 : if ((measured_times[max] - measured_times[min]) < maxdiff)
131 : 0 : return estimate;
132 : :
133 : : /* ok - drop the worse value and try again... */
134 : 0 : good_timer_sum = 0;
135 : 0 : good_timer_count = 0;
136 : 0 : if ((measured_times[max] - estimate) <
137 [ # # ]: 0 : (estimate - measured_times[min])) {
138 : 0 : printk(KERN_NOTICE "calibrate_delay_direct() dropping "
139 : : "min bogoMips estimate %d = %lu\n",
140 : : min, measured_times[min]);
141 : 0 : measured_times[min] = 0;
142 : 0 : min = max;
143 : : } else {
144 : 0 : printk(KERN_NOTICE "calibrate_delay_direct() dropping "
145 : : "max bogoMips estimate %d = %lu\n",
146 : : max, measured_times[max]);
147 : 0 : measured_times[max] = 0;
148 : 0 : max = min;
149 : : }
150 : :
151 [ # # ]: 0 : for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
152 [ # # ]: 0 : if (measured_times[i] == 0)
153 : 0 : continue;
154 : 0 : good_timer_count++;
155 : 0 : good_timer_sum += measured_times[i];
156 [ # # ]: 0 : if (measured_times[i] < measured_times[min])
157 : 0 : min = i;
158 [ # # ]: 0 : if (measured_times[i] > measured_times[max])
159 : 0 : max = i;
160 : : }
161 : :
162 : : }
163 : :
164 : 0 : 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 : 0 : return 0;
168 : : }
169 : : #else
170 : : static 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 : :
187 : 0 : static unsigned long calibrate_delay_converge(void)
188 : : {
189 : : /* First stage - slowly accelerate to find initial bounds */
190 : 0 : unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
191 : 0 : int trials = 0, band = 0, trial_in_band = 0;
192 : :
193 : 0 : lpj = (1<<12);
194 : :
195 : : /* wait for "start of" clock tick */
196 : 0 : ticks = jiffies;
197 : 0 : while (ticks == jiffies)
198 [ # # ]: 0 : ; /* nothing */
199 : : /* Go .. */
200 : 0 : ticks = jiffies;
201 : 0 : do {
202 [ # # ]: 0 : if (++trial_in_band == (1<<band)) {
203 : 0 : ++band;
204 : 0 : trial_in_band = 0;
205 : : }
206 : 0 : __delay(lpj * band);
207 : 0 : trials += band;
208 [ # # ]: 0 : } 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 : 0 : trials -= band;
214 : 0 : loopadd_base = lpj * band;
215 : 0 : lpj_base = lpj * trials;
216 : :
217 : 0 : recalibrate:
218 : 0 : lpj = lpj_base;
219 : 0 : 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 : 0 : chop_limit = lpj >> LPS_PREC;
226 [ # # ]: 0 : while (loopadd > chop_limit) {
227 : 0 : lpj += loopadd;
228 : 0 : ticks = jiffies;
229 : 0 : while (ticks == jiffies)
230 [ # # ]: 0 : ; /* nothing */
231 : 0 : ticks = jiffies;
232 : 0 : __delay(lpj);
233 [ # # ]: 0 : if (jiffies != ticks) /* longer than 1 tick */
234 : 0 : lpj -= loopadd;
235 : 0 : 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 [ # # ]: 0 : if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
243 : 0 : lpj_base = lpj;
244 : 0 : loopadd_base <<= 2;
245 : 0 : goto recalibrate;
246 : : }
247 : :
248 : 0 : return lpj;
249 : : }
250 : :
251 : : static 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 : : */
261 : 0 : unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
262 : : {
263 : 0 : 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 : :
271 : 78 : void __attribute__((weak)) calibration_delay_done(void)
272 : : {
273 : 78 : }
274 : :
275 : 78 : void calibrate_delay(void)
276 : : {
277 : 78 : unsigned long lpj;
278 : 78 : static bool printed;
279 [ - + ]: 78 : int this_cpu = smp_processor_id();
280 : :
281 [ - + ]: 78 : if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
282 : 0 : lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
283 [ # # ]: 0 : if (!printed)
284 : 0 : pr_info("Calibrating delay loop (skipped) "
285 : : "already calibrated this CPU");
286 [ + - ]: 78 : } else if (preset_lpj) {
287 : 78 : lpj = preset_lpj;
288 [ + - ]: 78 : if (!printed)
289 : 78 : pr_info("Calibrating delay loop (skipped) "
290 : : "preset value.. ");
291 [ # # # # ]: 0 : } else if ((!printed) && lpj_fine) {
292 : 0 : lpj = lpj_fine;
293 : 0 : pr_info("Calibrating delay loop (skipped), "
294 : : "value calculated using timer frequency.. ");
295 [ # # ]: 0 : } else if ((lpj = calibrate_delay_is_known())) {
296 : : ;
297 [ # # ]: 0 : } else if ((lpj = calibrate_delay_direct()) != 0) {
298 [ # # ]: 0 : if (!printed)
299 : 0 : pr_info("Calibrating delay using timer "
300 : : "specific routine.. ");
301 : : } else {
302 [ # # ]: 0 : if (!printed)
303 : 0 : pr_info("Calibrating delay loop... ");
304 : 0 : lpj = calibrate_delay_converge();
305 : : }
306 : 78 : per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
307 [ + - ]: 78 : if (!printed)
308 : 78 : pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
309 : : lpj/(500000/HZ),
310 : : (lpj/(5000/HZ)) % 100, lpj);
311 : :
312 : 78 : loops_per_jiffy = lpj;
313 : 78 : printed = true;
314 : :
315 : 78 : calibration_delay_done();
316 : 78 : }
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