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