LXR linux/arch/x86/include/asm/timer.h

   1#ifndef _ASM_X86_TIMER_H
   2#define _ASM_X86_TIMER_H
   3#include <linux/init.h>
   4#include <linux/pm.h>
   5#include <linux/percpu.h>
   6#include <linux/interrupt.h>
   7
   8#define TICK_SIZE (tick_nsec / 1000)
   9
  10unsigned long long native_sched_clock(void);
  11extern int recalibrate_cpu_khz(void);
  12
  13#if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC)
  14extern int timer_ack;
  15#else
  16# define timer_ack (0)
  17#endif
  18
  19extern int no_timer_check;
  20
  21/* Accelerators for sched_clock()
  22 * convert from cycles(64bits) => nanoseconds (64bits)
  23 *  basic equation:
  24 *              ns = cycles / (freq / ns_per_sec)
  25 *              ns = cycles * (ns_per_sec / freq)
  26 *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  27 *              ns = cycles * (10^6 / cpu_khz)
  28 *
  29 *      Then we use scaling math (suggested by george@mvista.com) to get:
  30 *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  31 *              ns = cycles * cyc2ns_scale / SC
  32 *
  33 *      And since SC is a constant power of two, we can convert the div
  34 *  into a shift.
  35 *
  36 *  We can use khz divisor instead of mhz to keep a better precision, since
  37 *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  38 *  (mathieu.desnoyers@polymtl.ca)
  39 *
  40 *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  41 */
  42
  43DECLARE_PER_CPU(unsigned long, cyc2ns);
  44DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
  45
  46#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  47
  48static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
  49{
  50        int cpu = smp_processor_id();
  51        unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
  52        ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR;
  53        return ns;
  54}
  55
  56static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  57{
  58        unsigned long long ns;
  59        unsigned long flags;
  60
  61        local_irq_save(flags);
  62        ns = __cycles_2_ns(cyc);
  63        local_irq_restore(flags);
  64
  65        return ns;
  66}
  67
  68#endif /* _ASM_X86_TIMER_H */
  69