]>
Commit | Line | Data |
---|---|---|
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 | static bool printed; | |
249 | ||
250 | if (preset_lpj) { | |
251 | loops_per_jiffy = preset_lpj; | |
252 | if (!printed) | |
253 | pr_info("Calibrating delay loop (skipped) " | |
254 | "preset value.. "); | |
255 | } else if ((!printed) && lpj_fine) { | |
256 | loops_per_jiffy = lpj_fine; | |
257 | pr_info("Calibrating delay loop (skipped), " | |
258 | "value calculated using timer frequency.. "); | |
259 | } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) { | |
260 | if (!printed) | |
261 | pr_info("Calibrating delay using timer " | |
262 | "specific routine.. "); | |
263 | } else { | |
264 | if (!printed) | |
265 | pr_info("Calibrating delay loop... "); | |
266 | loops_per_jiffy = calibrate_delay_converge(); | |
267 | } | |
268 | if (!printed) | |
269 | pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n", | |
270 | loops_per_jiffy/(500000/HZ), | |
271 | (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy); | |
272 | ||
273 | printed = true; | |
274 | } |