arch/arm/kernel/sched_clock.c

   1 /*
   2  * sched_clock.c: support for extending counters to full 64-bit ns counter
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8 #include <linux/clocksource.h>
   9 #include <linux/init.h>
  10 #include <linux/jiffies.h>
  11 #include <linux/kernel.h>
  12 #include <linux/sched.h>
  13 #include <linux/timer.h>
  14
  15 #include <asm/sched_clock.h>
  16
  17 static void sched_clock_poll(unsigned long wrap_ticks);
  18 static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
  19 static void (*sched_clock_update_fn)(void);
  20
  21 static void sched_clock_poll(unsigned long wrap_ticks)
  22 {
  23         mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
  24         sched_clock_update_fn();
  25 }
  26
  27 void __init init_sched_clock(struct clock_data *cd, void (*update)(void),
  28         unsigned int clock_bits, unsigned long rate)
  29 {
  30         unsigned long r, w;
  31         u64 res, wrap;
  32         char r_unit;
  33
  34         sched_clock_update_fn = update;
  35
  36         /* calculate the mult/shift to convert counter ticks to ns. */
  37         clocks_calc_mult_shift(&cd->mult, &cd->shift, rate, NSEC_PER_SEC, 0);
  38
  39         r = rate;
  40         if (r >= 4000000) {
  41                 r /= 1000000;
  42                 r_unit = 'M';
  43         } else {
  44                 r /= 1000;
  45                 r_unit = 'k';
  46         }
  47
  48         /* calculate how many ns until we wrap */
  49         wrap = cyc_to_ns((1ULL << clock_bits) - 1, cd->mult, cd->shift);
  50         do_div(wrap, NSEC_PER_MSEC);
  51         w = wrap;
  52
  53         /* calculate the ns resolution of this counter */
  54         res = cyc_to_ns(1ULL, cd->mult, cd->shift);
  55         pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
  56                 clock_bits, r, r_unit, res, w);
  57
  58         /*
  59          * Start the timer to keep sched_clock() properly updated and
  60          * sets the initial epoch.
  61          */
  62         sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
  63         update();
  64
  65         /*
  66          * Ensure that sched_clock() starts off at 0ns
  67          */
  68         cd->epoch_ns = 0;
  69 }
  70
  71 void __init sched_clock_postinit(void)
  72 {
  73         sched_clock_poll(sched_clock_timer.data);
  74 }