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/moduleparam.h>
  13 #include <linux/sched.h>
  14 #include <linux/syscore_ops.h>
  15 #include <linux/timer.h>
  16
  17 #include <asm/sched_clock.h>
  18
  19 struct clock_data {
  20         u64 epoch_ns;
  21         u32 epoch_cyc;
  22         u32 epoch_cyc_copy;
  23         unsigned long rate;
  24         u32 mult;
  25         u32 shift;
  26         bool suspended;
  27         bool needs_suspend;
  28 };
  29
  30 static void sched_clock_poll(unsigned long wrap_ticks);
  31 static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
  32 static int irqtime = -1;
  33
  34 core_param(irqtime, irqtime, int, 0400);
  35
  36 static struct clock_data cd = {
  37         .mult   = NSEC_PER_SEC / HZ,
  38 };
  39
  40 static u32 __read_mostly sched_clock_mask = 0xffffffff;
  41
  42 static u32 notrace jiffy_sched_clock_read(void)
  43 {
  44         return (u32)(jiffies - INITIAL_JIFFIES);
  45 }
  46
  47 static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
  48
  49 static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  50 {
  51         return (cyc * mult) >> shift;
  52 }
  53
  54 static unsigned long long notrace cyc_to_sched_clock(u32 cyc, u32 mask)
  55 {
  56         u64 epoch_ns;
  57         u32 epoch_cyc;
  58
  59         if (cd.suspended)
  60                 return cd.epoch_ns;
  61
  62         /*
  63          * Load the epoch_cyc and epoch_ns atomically.  We do this by
  64          * ensuring that we always write epoch_cyc, epoch_ns and
  65          * epoch_cyc_copy in strict order, and read them in strict order.
  66          * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
  67          * the middle of an update, and we should repeat the load.
  68          */
  69         do {
  70                 epoch_cyc = cd.epoch_cyc;
  71                 smp_rmb();
  72                 epoch_ns = cd.epoch_ns;
  73                 smp_rmb();
  74         } while (epoch_cyc != cd.epoch_cyc_copy);
  75
  76         return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, cd.mult, cd.shift);
  77 }
  78
  79 /*
  80  * Atomically update the sched_clock epoch.
  81  */
  82 static void notrace update_sched_clock(void)
  83 {
  84         unsigned long flags;
  85         u32 cyc;
  86         u64 ns;
  87
  88         cyc = read_sched_clock();
  89         ns = cd.epoch_ns +
  90                 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
  91                           cd.mult, cd.shift);
  92         /*
  93          * Write epoch_cyc and epoch_ns in a way that the update is
  94          * detectable in cyc_to_fixed_sched_clock().
  95          */
  96         raw_local_irq_save(flags);
  97         cd.epoch_cyc_copy = cyc;
  98         smp_wmb();
  99         cd.epoch_ns = ns;
 100         smp_wmb();
 101         cd.epoch_cyc = cyc;
 102         raw_local_irq_restore(flags);
 103 }
 104
 105 static void sched_clock_poll(unsigned long wrap_ticks)
 106 {
 107         mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
 108         update_sched_clock();
 109 }
 110
 111 void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
 112 {
 113         unsigned long r, w;
 114         u64 res, wrap;
 115         char r_unit;
 116
 117         if (cd.rate > rate)
 118                 return;
 119
 120         BUG_ON(bits > 32);
 121         WARN_ON(!irqs_disabled());
 122         read_sched_clock = read;
 123         sched_clock_mask = (1 << bits) - 1;
 124         cd.rate = rate;
 125
 126         /* calculate the mult/shift to convert counter ticks to ns. */
 127         clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 0);
 128
 129         r = rate;
 130         if (r >= 4000000) {
 131                 r /= 1000000;
 132                 r_unit = 'M';
 133         } else if (r >= 1000) {
 134                 r /= 1000;
 135                 r_unit = 'k';
 136         } else
 137                 r_unit = ' ';
 138
 139         /* calculate how many ns until we wrap */
 140         wrap = cyc_to_ns((1ULL << bits) - 1, cd.mult, cd.shift);
 141         do_div(wrap, NSEC_PER_MSEC);
 142         w = wrap;
 143
 144         /* calculate the ns resolution of this counter */
 145         res = cyc_to_ns(1ULL, cd.mult, cd.shift);
 146         pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
 147                 bits, r, r_unit, res, w);
 148
 149         /*
 150          * Start the timer to keep sched_clock() properly updated and
 151          * sets the initial epoch.
 152          */
 153         sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
 154         update_sched_clock();
 155
 156         /*
 157          * Ensure that sched_clock() starts off at 0ns
 158          */
 159         cd.epoch_ns = 0;
 160
 161         /* Enable IRQ time accounting if we have a fast enough sched_clock */
 162         if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
 163                 enable_sched_clock_irqtime();
 164
 165         pr_debug("Registered %pF as sched_clock source\n", read);
 166 }
 167
 168 static unsigned long long notrace sched_clock_32(void)
 169 {
 170         u32 cyc = read_sched_clock();
 171         return cyc_to_sched_clock(cyc, sched_clock_mask);
 172 }
 173
 174 unsigned long long __read_mostly (*sched_clock_func)(void) = sched_clock_32;
 175
 176 unsigned long long notrace sched_clock(void)
 177 {
 178         return sched_clock_func();
 179 }
 180
 181 void __init sched_clock_postinit(void)
 182 {
 183         /*
 184          * If no sched_clock function has been provided at that point,
 185          * make it the final one one.
 186          */
 187         if (read_sched_clock == jiffy_sched_clock_read)
 188                 setup_sched_clock(jiffy_sched_clock_read, 32, HZ);
 189
 190         sched_clock_poll(sched_clock_timer.data);
 191 }
 192
 193 static int sched_clock_suspend(void)
 194 {
 195         sched_clock_poll(sched_clock_timer.data);
 196         cd.suspended = true;
 197         return 0;
 198 }
 199
 200 static void sched_clock_resume(void)
 201 {
 202         cd.epoch_cyc = read_sched_clock();
 203         cd.epoch_cyc_copy = cd.epoch_cyc;
 204         cd.suspended = false;
 205 }
 206
 207 static struct syscore_ops sched_clock_ops = {
 208         .suspend = sched_clock_suspend,
 209         .resume = sched_clock_resume,
 210 };
 211
 212 static int __init sched_clock_syscore_init(void)
 213 {
 214         register_syscore_ops(&sched_clock_ops);
 215         return 0;
 216 }
 217 device_initcall(sched_clock_syscore_init);