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 9 unsigned long long native_sched_clock(void); 10 unsigned long native_calibrate_tsc(void); 11 12 #ifdef CONFIG_X86_32 13 extern int timer_ack; 14 extern int recalibrate_cpu_khz(void); 15 #endif /* CONFIG_X86_32 */ 16 17 extern 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 45 DECLARE_PER_CPU(unsigned long, cyc2ns); 46 47 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ 48 49 static 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 54 static 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 */ 67