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 #include <linux/interrupt.h>
7
8 #define TICK_SIZE (tick_nsec / 1000)
9
10 unsigned long long native_sched_clock(void);
11 extern int recalibrate_cpu_khz(void);
12
13 extern int no_timer_check;
14
15 /* Accelerators for sched_clock()
16 * convert from cycles(64bits) => nanoseconds (64bits)
17 * basic equation:
18 * ns = cycles / (freq / ns_per_sec)
19 * ns = cycles * (ns_per_sec / freq)
20 * ns = cycles * (10^9 / (cpu_khz * 10^3))
21 * ns = cycles * (10^6 / cpu_khz)
22 *
23 * Then we use scaling math (suggested by george@mvista.com) to get:
24 * ns = cycles * (10^6 * SC / cpu_khz) / SC
25 * ns = cycles * cyc2ns_scale / SC
26 *
27 * And since SC is a constant power of two, we can convert the div
28 * into a shift.
29 *
30 * We can use khz divisor instead of mhz to keep a better precision, since
31 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
32 * (mathieu.desnoyers@polymtl.ca)
33 *
34 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
35 *
36 * In:
37 *
38 * ns = cycles * cyc2ns_scale / SC
39 *
40 * Although we may still have enough bits to store the value of ns,
41 * in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
42 * leading to an incorrect result.
43 *
44 * To avoid this, we can decompose 'cycles' into quotient and remainder
45 * of division by SC. Then,
46 *
47 * ns = (quot * SC + rem) * cyc2ns_scale / SC
48 * = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
49 *
50 * - sqazi@google.com
51 */
52
53 DECLARE_PER_CPU(unsigned long, cyc2ns);
54 DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
55
56 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
57
__cycles_2_ns(unsigned long long cyc)58 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
59 {
60 int cpu = smp_processor_id();
61 unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
62 ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
63 (1UL << CYC2NS_SCALE_FACTOR));
64 return ns;
65 }
66
cycles_2_ns(unsigned long long cyc)67 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
68 {
69 unsigned long long ns;
70 unsigned long flags;
71
72 local_irq_save(flags);
73 ns = __cycles_2_ns(cyc);
74 local_irq_restore(flags);
75
76 return ns;
77 }
78
79 #endif /* _ASM_X86_TIMER_H */
80