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
14 unsigned long lpj_fine;
15 unsigned long preset_lpj;
lpj_setup(char * str)16 static 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
calibrate_delay_direct(void)34 static unsigned long __cpuinit 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
calibrate_delay_direct(void)169 static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
170 #endif
171
172 /*
173 * This is the number of bits of precision for the loops_per_jiffy. Each
174 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
175 * to start with a good estimate.
176 * For the boot cpu we can skip the delay calibration and assign it a value
177 * calculated based on the timer frequency.
178 * For the rest of the CPUs we cannot assume that the timer frequency is same as
179 * the cpu frequency, hence do the calibration for those.
180 */
181 #define LPS_PREC 8
182
calibrate_delay_converge(void)183 static unsigned long __cpuinit calibrate_delay_converge(void)
184 {
185 /* First stage - slowly accelerate to find initial bounds */
186 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
187 int trials = 0, band = 0, trial_in_band = 0;
188
189 lpj = (1<<12);
190
191 /* wait for "start of" clock tick */
192 ticks = jiffies;
193 while (ticks == jiffies)
194 ; /* nothing */
195 /* Go .. */
196 ticks = jiffies;
197 do {
198 if (++trial_in_band == (1<<band)) {
199 ++band;
200 trial_in_band = 0;
201 }
202 __delay(lpj * band);
203 trials += band;
204 } while (ticks == jiffies);
205 /*
206 * We overshot, so retreat to a clear underestimate. Then estimate
207 * the largest likely undershoot. This defines our chop bounds.
208 */
209 trials -= band;
210 loopadd_base = lpj * band;
211 lpj_base = lpj * trials;
212
213 recalibrate:
214 lpj = lpj_base;
215 loopadd = loopadd_base;
216
217 /*
218 * Do a binary approximation to get lpj set to
219 * equal one clock (up to LPS_PREC bits)
220 */
221 chop_limit = lpj >> LPS_PREC;
222 while (loopadd > chop_limit) {
223 lpj += loopadd;
224 ticks = jiffies;
225 while (ticks == jiffies)
226 ; /* nothing */
227 ticks = jiffies;
228 __delay(lpj);
229 if (jiffies != ticks) /* longer than 1 tick */
230 lpj -= loopadd;
231 loopadd >>= 1;
232 }
233 /*
234 * If we incremented every single time possible, presume we've
235 * massively underestimated initially, and retry with a higher
236 * start, and larger range. (Only seen on x86_64, due to SMIs)
237 */
238 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
239 lpj_base = lpj;
240 loopadd_base <<= 2;
241 goto recalibrate;
242 }
243
244 return lpj;
245 }
246
247 static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
248
249 /*
250 * Check if cpu calibration delay is already known. For example,
251 * some processors with multi-core sockets may have all cores
252 * with the same calibration delay.
253 *
254 * Architectures should override this function if a faster calibration
255 * method is available.
256 */
calibrate_delay_is_known(void)257 unsigned long __attribute__((weak)) __cpuinit calibrate_delay_is_known(void)
258 {
259 return 0;
260 }
261
calibrate_delay(void)262 void __cpuinit calibrate_delay(void)
263 {
264 unsigned long lpj;
265 static bool printed;
266 int this_cpu = smp_processor_id();
267
268 if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
269 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
270 if (!printed)
271 pr_info("Calibrating delay loop (skipped) "
272 "already calibrated this CPU");
273 } else if (preset_lpj) {
274 lpj = preset_lpj;
275 if (!printed)
276 pr_info("Calibrating delay loop (skipped) "
277 "preset value.. ");
278 } else if ((!printed) && lpj_fine) {
279 lpj = lpj_fine;
280 pr_info("Calibrating delay loop (skipped), "
281 "value calculated using timer frequency.. ");
282 } else if ((lpj = calibrate_delay_is_known())) {
283 ;
284 } else if ((lpj = calibrate_delay_direct()) != 0) {
285 if (!printed)
286 pr_info("Calibrating delay using timer "
287 "specific routine.. ");
288 } else {
289 if (!printed)
290 pr_info("Calibrating delay loop... ");
291 lpj = calibrate_delay_converge();
292 }
293 per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
294 if (!printed)
295 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
296 lpj/(500000/HZ),
297 (lpj/(5000/HZ)) % 100, lpj);
298
299 loops_per_jiffy = lpj;
300 printed = true;
301 }
302