diff options
Diffstat (limited to 'arch/x86/include/asm/timer.h')
| -rw-r--r-- | arch/x86/include/asm/timer.h | 78 |
1 files changed, 18 insertions, 60 deletions
diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h index 34baa0e..a04eabd 100644 --- a/arch/x86/include/asm/timer.h +++ b/arch/x86/include/asm/timer.h @@ -1,9 +1,9 @@ #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> +#include <linux/math64.h> #define TICK_SIZE (tick_nsec / 1000) @@ -12,68 +12,26 @@ extern int recalibrate_cpu_khz(void); 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) +/* + * We use the full linear equation: f(x) = a + b*x, in order to allow + * a continuous function in the face of dynamic freq changes. * - * 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 + * Continuity means that when our frequency changes our slope (b); we want to + * ensure that: f(t) == f'(t), which gives: a + b*t == a' + b'*t. * - * And since SC is a constant power of two, we can convert the div - * into a shift. + * Without an offset (a) the above would not be possible. * - * 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!" - * - * In: - * - * ns = cycles * cyc2ns_scale / SC - * - * Although we may still have enough bits to store the value of ns, - * in some cases, we may not have enough bits to store cycles * cyc2ns_scale, - * leading to an incorrect result. - * - * To avoid this, we can decompose 'cycles' into quotient and remainder - * of division by SC. Then, - * - * ns = (quot * SC + rem) * cyc2ns_scale / SC - * = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC - * - * - sqazi@google.com + * See the comment near cycles_2_ns() for details on how we compute (b). */ - -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 += mult_frac(cyc, per_cpu(cyc2ns, cpu), - (1UL << 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; -} +struct cyc2ns_data { + u32 cyc2ns_mul; + u32 cyc2ns_shift; + u64 cyc2ns_offset; + u32 __count; + /* u32 hole */ +}; /* 24 bytes -- do not grow */ + +extern struct cyc2ns_data *cyc2ns_read_begin(void); +extern void cyc2ns_read_end(struct cyc2ns_data *); #endif /* _ASM_X86_TIMER_H */ |