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Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
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
7#define TICK_SIZE (tick_nsec / 1000)
8
9unsigned long long native_sched_clock(void);
10unsigned long native_calibrate_tsc(void);
11
12#ifdef CONFIG_X86_32
13extern int timer_ack;
14extern int recalibrate_cpu_khz(void);
15#endif /* CONFIG_X86_32 */
16
17extern int no_timer_check;
18
19#ifndef CONFIG_PARAVIRT
20#define calibrate_tsc() native_calibrate_tsc()
21#endif
22
23/* Accelerators for sched_clock()
24 * convert from cycles(64bits) => nanoseconds (64bits)
25 * basic equation:
26 * ns = cycles / (freq / ns_per_sec)
27 * ns = cycles * (ns_per_sec / freq)
28 * ns = cycles * (10^9 / (cpu_khz * 10^3))
29 * ns = cycles * (10^6 / cpu_khz)
30 *
31 * Then we use scaling math (suggested by george@mvista.com) to get:
32 * ns = cycles * (10^6 * SC / cpu_khz) / SC
33 * ns = cycles * cyc2ns_scale / SC
34 *
35 * And since SC is a constant power of two, we can convert the div
36 * into a shift.
37 *
38 * We can use khz divisor instead of mhz to keep a better precision, since
39 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
40 * (mathieu.desnoyers@polymtl.ca)
41 *
42 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
43 */
44
45DECLARE_PER_CPU(unsigned long, cyc2ns);
46
47#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
48
49static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
50{
51 return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;
52}
53
54static inline unsigned long long cycles_2_ns(unsigned long long cyc)
55{
56 unsigned long long ns;
57 unsigned long flags;
58
59 local_irq_save(flags);
60 ns = __cycles_2_ns(cyc);
61 local_irq_restore(flags);
62
63 return ns;
64}
65
66#endif /* _ASM_X86_TIMER_H */