1 #ifndef _ASM_X86_TIMER_H
2 #define _ASM_X86_TIMER_H
3 #include <linux/init.h>
5 #include <linux/percpu.h>
6 #include <linux/interrupt.h>
8 #define TICK_SIZE (tick_nsec / 1000)
10 unsigned long long native_sched_clock(void);
11 unsigned long native_calibrate_tsc(void);
16 extern int recalibrate_cpu_khz(void);
18 extern int no_timer_check;
20 #ifndef CONFIG_PARAVIRT
21 #define calibrate_tsc() native_calibrate_tsc()
24 /* Accelerators for sched_clock()
25 * convert from cycles(64bits) => nanoseconds (64bits)
27 * ns = cycles / (freq / ns_per_sec)
28 * ns = cycles * (ns_per_sec / freq)
29 * ns = cycles * (10^9 / (cpu_khz * 10^3))
30 * ns = cycles * (10^6 / cpu_khz)
32 * Then we use scaling math (suggested by george@mvista.com) to get:
33 * ns = cycles * (10^6 * SC / cpu_khz) / SC
34 * ns = cycles * cyc2ns_scale / SC
36 * And since SC is a constant power of two, we can convert the div
39 * We can use khz divisor instead of mhz to keep a better precision, since
40 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
41 * (mathieu.desnoyers@polymtl.ca)
43 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
46 DECLARE_PER_CPU(unsigned long, cyc2ns);
47 DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
49 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
51 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
53 int cpu = smp_processor_id();
54 unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
55 ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR;
59 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
61 unsigned long long ns;
64 local_irq_save(flags);
65 ns = __cycles_2_ns(cyc);
66 local_irq_restore(flags);
71 #endif /* _ASM_X86_TIMER_H */