#ifndef _ASM_X86_TIMER_H #define _ASM_X86_TIMER_H #include <linux/init.h> #include <linux/pm.h> #include <linux/percpu.h> #include <linux/interrupt.h> #define TICK_SIZE (tick_nsec / 1000) unsigned long long native_sched_clock(void); extern int recalibrate_cpu_khz(void); #if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC) extern int timer_ack; #else # define timer_ack (0) #endif extern int no_timer_check; /* Accelerators for sched_clock() * convert from cycles(64bits) => nanoseconds (64bits) * basic equation: * ns = cycles / (freq / ns_per_sec) * ns = cycles * (ns_per_sec / freq) * ns = cycles * (10^9 / (cpu_khz * 10^3)) * ns = cycles * (10^6 / cpu_khz) * * Then we use scaling math (suggested by george@mvista.com) to get: * ns = cycles * (10^6 * SC / cpu_khz) / SC * ns = cycles * cyc2ns_scale / SC * * And since SC is a constant power of two, we can convert the div * into a shift. * * We can use khz divisor instead of mhz to keep a better precision, since * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits. * (mathieu.desnoyers@polymtl.ca) * * -johnstul@us.ibm.com "math is hard, lets go shopping!" */ DECLARE_PER_CPU(unsigned long, cyc2ns); DECLARE_PER_CPU(unsigned long long, cyc2ns_offset); #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ static inline unsigned long long __cycles_2_ns(unsigned long long cyc) { int cpu = smp_processor_id(); unsigned long long ns = per_cpu(cyc2ns_offset, cpu); ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR; return ns; } static inline unsigned long long cycles_2_ns(unsigned long long cyc) { unsigned long long ns; unsigned long flags; local_irq_save(flags); ns = __cycles_2_ns(cyc); local_irq_restore(flags); return ns; } #endif /* _ASM_X86_TIMER_H */