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 unsigned long native_calibrate_tsc(void); 12 13 #ifdef CONFIG_X86_32 14 extern int timer_ack; 15 extern irqreturn_t timer_interrupt(int irq, void *dev_id); 16 #endif /* CONFIG_X86_32 */ 17 extern int recalibrate_cpu_khz(void); 18 19 extern int no_timer_check; 20 21 #ifndef CONFIG_PARAVIRT 22 #define calibrate_tsc() native_calibrate_tsc() 23 #endif 24 25 /* Accelerators for sched_clock() 26 * convert from cycles(64bits) => nanoseconds (64bits) 27 * basic equation: 28 * ns = cycles / (freq / ns_per_sec) 29 * ns = cycles * (ns_per_sec / freq) 30 * ns = cycles * (10^9 / (cpu_khz * 10^3)) 31 * ns = cycles * (10^6 / cpu_khz) 32 * 33 * Then we use scaling math (suggested by george@mvista.com) to get: 34 * ns = cycles * (10^6 * SC / cpu_khz) / SC 35 * ns = cycles * cyc2ns_scale / SC 36 * 37 * And since SC is a constant power of two, we can convert the div 38 * into a shift. 39 * 40 * We can use khz divisor instead of mhz to keep a better precision, since 41 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits. 42 * (mathieu.desnoyers@polymtl.ca) 43 * 44 * -johnstul@us.ibm.com "math is hard, lets go shopping!" 45 */ 46 47 DECLARE_PER_CPU(unsigned long, cyc2ns); 48 49 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ 50 51 static inline unsigned long long __cycles_2_ns(unsigned long long cyc) 52 { 53 return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR; 54 } 55 56 static inline unsigned long long cycles_2_ns(unsigned long long cyc) 57 { 58 unsigned long long ns; 59 unsigned long flags; 60 61 local_irq_save(flags); 62 ns = __cycles_2_ns(cyc); 63 local_irq_restore(flags); 64 65 return ns; 66 } 67 68 #endif /* _ASM_X86_TIMER_H */ 69