Linux kernel mirror (for testing)
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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
8unsigned long long native_sched_clock(void);
9unsigned long native_calculate_cpu_khz(void);
10
11extern int timer_ack;
12extern int no_timer_check;
13extern 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 */
40extern unsigned long cyc2ns_scale __read_mostly;
41
42#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
43
44static 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