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