init/calibrate.c

   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                 printk(KERN_DEBUG "calibrate_delay_direct() timer_rate_max=%lu "
  97                             "timer_rate_min=%lu pre_start=%lu pre_end=%lu\n",
  98                           timer_rate_max, timer_rate_min, pre_start, pre_end);
  99                 if (start >= post_end)
 100                         printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
 101                                         "timer_rate as we had a TSC wrap around"
 102                                         " start=%lu >=post_end=%lu\n",
 103                                 start, post_end);
 104                 if (start < post_end && pre_start != 0 && pre_end != 0 &&
 105                     (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
 106                         good_timer_count++;
 107                         good_timer_sum += timer_rate_max;
 108                         measured_times[i] = timer_rate_max;
 109                         if (max < 0 || timer_rate_max > measured_times[max])
 110                                 max = i;
 111                         if (min < 0 || timer_rate_max < measured_times[min])
 112                                 min = i;
 113                 } else
 114                         measured_times[i] = 0;
 115
 116         }
 117
 118         /*
 119          * Find the maximum & minimum - if they differ too much throw out the
 120          * one with the largest difference from the mean and try again...
 121          */
 122         while (good_timer_count > 1) {
 123                 unsigned long estimate;
 124                 unsigned long maxdiff;
 125
 126                 /* compute the estimate */
 127                 estimate = (good_timer_sum/good_timer_count);
 128                 maxdiff = estimate >> 3;
 129
 130                 /* if range is within 12% let's take it */
 131                 if ((measured_times[max] - measured_times[min]) < maxdiff)
 132                         return estimate;
 133
 134                 /* ok - drop the worse value and try again... */
 135                 good_timer_sum = 0;
 136                 good_timer_count = 0;
 137                 if ((measured_times[max] - estimate) <
 138                                 (estimate - measured_times[min])) {
 139                         printk(KERN_NOTICE "calibrate_delay_direct() dropping "
 140                                         "min bogoMips estimate %d = %lu\n",
 141                                 min, measured_times[min]);
 142                         measured_times[min] = 0;
 143                         min = max;
 144                 } else {
 145                         printk(KERN_NOTICE "calibrate_delay_direct() dropping "
 146                                         "max bogoMips estimate %d = %lu\n",
 147                                 max, measured_times[max]);
 148                         measured_times[max] = 0;
 149                         max = min;
 150                 }
 151
 152                 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
 153                         if (measured_times[i] == 0)
 154                                 continue;
 155                         good_timer_count++;
 156                         good_timer_sum += measured_times[i];
 157                         if (measured_times[i] < measured_times[min])
 158                                 min = i;
 159                         if (measured_times[i] > measured_times[max])
 160                                 max = i;
 161                 }
 162
 163         }
 164
 165         printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
 166                "estimate for loops_per_jiffy.\nProbably due to long platform "
 167                 "interrupts. Consider using \"lpj=\" boot option.\n");
 168         return 0;
 169 }
 170 #else
 171 static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
 172 #endif
 173
 174 /*
 175  * This is the number of bits of precision for the loops_per_jiffy.  Each
 176  * time we refine our estimate after the first takes 1.5/HZ seconds, so try
 177  * to start with a good estimate.
 178  * For the boot cpu we can skip the delay calibration and assign it a value
 179  * calculated based on the timer frequency.
 180  * For the rest of the CPUs we cannot assume that the timer frequency is same as
 181  * the cpu frequency, hence do the calibration for those.
 182  */
 183 #define LPS_PREC 8
 184
 185 static unsigned long __cpuinit calibrate_delay_converge(void)
 186 {
 187         /* First stage - slowly accelerate to find initial bounds */
 188         unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
 189         int trials = 0, band = 0, trial_in_band = 0;
 190
 191         lpj = (1<<12);
 192
 193         /* wait for "start of" clock tick */
 194         ticks = jiffies;
 195         while (ticks == jiffies)
 196                 ; /* nothing */
 197         /* Go .. */
 198         ticks = jiffies;
 199         do {
 200                 if (++trial_in_band == (1<<band)) {
 201                         ++band;
 202                         trial_in_band = 0;
 203                 }
 204                 __delay(lpj * band);
 205                 trials += band;
 206         } while (ticks == jiffies);
 207         /*
 208          * We overshot, so retreat to a clear underestimate. Then estimate
 209          * the largest likely undershoot. This defines our chop bounds.
 210          */
 211         trials -= band;
 212         loopadd_base = lpj * band;
 213         lpj_base = lpj * trials;
 214
 215 recalibrate:
 216         lpj = lpj_base;
 217         loopadd = loopadd_base;
 218
 219         /*
 220          * Do a binary approximation to get lpj set to
 221          * equal one clock (up to LPS_PREC bits)
 222          */
 223         chop_limit = lpj >> LPS_PREC;
 224         while (loopadd > chop_limit) {
 225                 lpj += loopadd;
 226                 ticks = jiffies;
 227                 while (ticks == jiffies)
 228                         ; /* nothing */
 229                 ticks = jiffies;
 230                 __delay(lpj);
 231                 if (jiffies != ticks)   /* longer than 1 tick */
 232                         lpj -= loopadd;
 233                 loopadd >>= 1;
 234         }
 235         /*
 236          * If we incremented every single time possible, presume we've
 237          * massively underestimated initially, and retry with a higher
 238          * start, and larger range. (Only seen on x86_64, due to SMIs)
 239          */
 240         if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
 241                 lpj_base = lpj;
 242                 loopadd_base <<= 2;
 243                 goto recalibrate;
 244         }
 245
 246         return lpj;
 247 }
 248
 249 void __cpuinit calibrate_delay(void)
 250 {
 251         static bool printed;
 252
 253         if (preset_lpj) {
 254                 loops_per_jiffy = preset_lpj;
 255                 if (!printed)
 256                         pr_info("Calibrating delay loop (skipped) "
 257                                 "preset value.. ");
 258         } else if ((!printed) && lpj_fine) {
 259                 loops_per_jiffy = lpj_fine;
 260                 pr_info("Calibrating delay loop (skipped), "
 261                         "value calculated using timer frequency.. ");
 262         } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
 263                 if (!printed)
 264                         pr_info("Calibrating delay using timer "
 265                                 "specific routine.. ");
 266         } else {
 267                 if (!printed)
 268                         pr_info("Calibrating delay loop... ");
 269                 loops_per_jiffy = calibrate_delay_converge();
 270         }
 271         if (!printed)
 272                 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
 273                         loops_per_jiffy/(500000/HZ),
 274                         (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
 275
 276         printed = true;
 277 }