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#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
12extern int timer_ack;
13extern int no_timer_check;
14extern int recalibrate_cpu_khz(void);
15
16#ifndef CONFIG_PARAVIRT
17#define calibrate_tsc() native_calibrate_tsc()
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
42DECLARE_PER_CPU(unsigned long, cyc2ns);
43
44#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
45
46static 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
51static 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