arch/arm/include/asm/sched_clock.h

   1 /*
   2  * sched_clock.h: 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 #ifndef ASM_SCHED_CLOCK
   9 #define ASM_SCHED_CLOCK
  10
  11 #include <linux/kernel.h>
  12 #include <linux/types.h>
  13
  14 struct clock_data {
  15         u64 epoch_ns;
  16         u32 epoch_cyc;
  17         u32 epoch_cyc_copy;
  18         u32 mult;
  19         u32 shift;
  20 };
  21
  22 #define DEFINE_CLOCK_DATA(name) struct clock_data name
  23
  24 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  25 {
  26         return (cyc * mult) >> shift;
  27 }
  28
  29 /*
  30  * Atomically update the sched_clock epoch.  Your update callback will
  31  * be called from a timer before the counter wraps - read the current
  32  * counter value, and call this function to safely move the epochs
  33  * forward.  Only use this from the update callback.
  34  */
  35 static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
  36 {
  37         unsigned long flags;
  38         u64 ns = cd->epoch_ns +
  39                 cyc_to_ns((cyc - cd->epoch_cyc) & mask, cd->mult, cd->shift);
  40
  41         /*
  42          * Write epoch_cyc and epoch_ns in a way that the update is
  43          * detectable in cyc_to_fixed_sched_clock().
  44          */
  45         raw_local_irq_save(flags);
  46         cd->epoch_cyc = cyc;
  47         smp_wmb();
  48         cd->epoch_ns = ns;
  49         smp_wmb();
  50         cd->epoch_cyc_copy = cyc;
  51         raw_local_irq_restore(flags);
  52 }
  53
  54 /*
  55  * If your clock rate is known at compile time, using this will allow
  56  * you to optimize the mult/shift loads away.  This is paired with
  57  * init_fixed_sched_clock() to ensure that your mult/shift are correct.
  58  */
  59 static inline unsigned long long cyc_to_fixed_sched_clock(struct clock_data *cd,
  60         u32 cyc, u32 mask, u32 mult, u32 shift)
  61 {
  62         u64 epoch_ns;
  63         u32 epoch_cyc;
  64
  65         /*
  66          * Load the epoch_cyc and epoch_ns atomically.  We do this by
  67          * ensuring that we always write epoch_cyc, epoch_ns and
  68          * epoch_cyc_copy in strict order, and read them in strict order.
  69          * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
  70          * the middle of an update, and we should repeat the load.
  71          */
  72         do {
  73                 epoch_cyc = cd->epoch_cyc;
  74                 smp_rmb();
  75                 epoch_ns = cd->epoch_ns;
  76                 smp_rmb();
  77         } while (epoch_cyc != cd->epoch_cyc_copy);
  78
  79         return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, mult, shift);
  80 }
  81
  82 /*
  83  * Otherwise, you need to use this, which will obtain the mult/shift
  84  * from the clock_data structure.  Use init_sched_clock() with this.
  85  */
  86 static inline unsigned long long cyc_to_sched_clock(struct clock_data *cd,
  87         u32 cyc, u32 mask)
  88 {
  89         return cyc_to_fixed_sched_clock(cd, cyc, mask, cd->mult, cd->shift);
  90 }
  91
  92 /*
  93  * Initialize the clock data - calculate the appropriate multiplier
  94  * and shift.  Also setup a timer to ensure that the epoch is refreshed
  95  * at the appropriate time interval, which will call your update
  96  * handler.
  97  */
  98 void init_sched_clock(struct clock_data *, void (*)(void),
  99         unsigned int, unsigned long);
 100
 101 /*
 102  * Use this initialization function rather than init_sched_clock() if
 103  * you're using cyc_to_fixed_sched_clock, which will warn if your
 104  * constants are incorrect.
 105  */
 106 static inline void init_fixed_sched_clock(struct clock_data *cd,
 107         void (*update)(void), unsigned int bits, unsigned long rate,
 108         u32 mult, u32 shift)
 109 {
 110         init_sched_clock(cd, update, bits, rate);
 111         if (cd->mult != mult || cd->shift != shift) {
 112                 pr_crit("sched_clock: wrong multiply/shift: %u>>%u vs calculated %u>>%u\n"
 113                         "sched_clock: fix multiply/shift to avoid scheduler hiccups\n",
 114                         mult, shift, cd->mult, cd->shift);
 115         }
 116 }
 117
 118 extern void sched_clock_postinit(void);
 119
 120 #endif