include/asm-x86/timer.h

   1 #ifndef _ASMi386_TIMER_H
   2 #define _ASMi386_TIMER_H
   3 #include <linux/init.h>
   4 #include <linux/pm.h>
   5
   6 #define TICK_SIZE (tick_nsec / 1000)
   7
   8 unsigned long long native_sched_clock(void);
   9 unsigned long native_calculate_cpu_khz(void);
  10
  11 extern int timer_ack;
  12 extern int no_timer_check;
  13 extern int recalibrate_cpu_khz(void);
  14
  15 #ifndef CONFIG_PARAVIRT
  16 #define calculate_cpu_khz() native_calculate_cpu_khz()
  17 #endif
  18
  19 /* Accellerators for sched_clock()
  20  * convert from cycles(64bits) => nanoseconds (64bits)
  21  *  basic equation:
  22  *              ns = cycles / (freq / ns_per_sec)
  23  *              ns = cycles * (ns_per_sec / freq)
  24  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  25  *              ns = cycles * (10^6 / cpu_khz)
  26  *
  27  *      Then we use scaling math (suggested by george@mvista.com) to get:
  28  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  29  *              ns = cycles * cyc2ns_scale / SC
  30  *
  31  *      And since SC is a constant power of two, we can convert the div
  32  *  into a shift.
  33  *
  34  *  We can use khz divisor instead of mhz to keep a better percision, since
  35  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  36  *  (mathieu.desnoyers@polymtl.ca)
  37  *
  38  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  39  */
  40 extern unsigned long cyc2ns_scale __read_mostly;
  41
  42 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  43
  44 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  45 {
  46         return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
  47 }
  48
  49
  50 #endif