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