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