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