Root/
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; |
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 | |
34 | static 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 |
169 | static 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 | |
186 | static 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 | |
216 | recalibrate: |
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 | |
250 | static 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 | */ |
260 | unsigned long __attribute__((weak)) calibrate_delay_is_known(void) |
261 | { |
262 | return 0; |
263 | } |
264 | |
265 | void calibrate_delay(void) |
266 | { |
267 | unsigned long lpj; |
268 | static bool printed; |
269 | int this_cpu = smp_processor_id(); |
270 | |
271 | if (per_cpu(cpu_loops_per_jiffy, this_cpu)) { |
272 | lpj = per_cpu(cpu_loops_per_jiffy, this_cpu); |
273 | if (!printed) |
274 | pr_info("Calibrating delay loop (skipped) " |
275 | "already calibrated this CPU"); |
276 | } else if (preset_lpj) { |
277 | lpj = preset_lpj; |
278 | if (!printed) |
279 | pr_info("Calibrating delay loop (skipped) " |
280 | "preset value.. "); |
281 | } else if ((!printed) && lpj_fine) { |
282 | lpj = lpj_fine; |
283 | pr_info("Calibrating delay loop (skipped), " |
284 | "value calculated using timer frequency.. "); |
285 | } else if ((lpj = calibrate_delay_is_known())) { |
286 | ; |
287 | } else if ((lpj = calibrate_delay_direct()) != 0) { |
288 | if (!printed) |
289 | pr_info("Calibrating delay using timer " |
290 | "specific routine.. "); |
291 | } else { |
292 | if (!printed) |
293 | pr_info("Calibrating delay loop... "); |
294 | lpj = calibrate_delay_converge(); |
295 | } |
296 | per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj; |
297 | if (!printed) |
298 | pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n", |
299 | lpj/(500000/HZ), |
300 | (lpj/(5000/HZ)) % 100, lpj); |
301 | |
302 | loops_per_jiffy = lpj; |
303 | printed = true; |
304 | } |
305 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9