diff options
Diffstat (limited to 'arch/x86/kernel/tsc_64.c')
| -rw-r--r-- | arch/x86/kernel/tsc_64.c | 57 |
1 files changed, 47 insertions, 10 deletions
diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c index 9c70af45b42..32edd2c50e9 100644 --- a/arch/x86/kernel/tsc_64.c +++ b/arch/x86/kernel/tsc_64.c @@ -10,6 +10,7 @@ #include <asm/hpet.h> #include <asm/timex.h> +#include <asm/timer.h> static int notsc __initdata = 0; @@ -18,16 +19,48 @@ EXPORT_SYMBOL(cpu_khz); unsigned int tsc_khz; EXPORT_SYMBOL(tsc_khz); -static unsigned int cyc2ns_scale __read_mostly; +/* 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!" + */ +DEFINE_PER_CPU(unsigned long, cyc2ns); -static inline void set_cyc2ns_scale(unsigned long khz) +static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu) { - cyc2ns_scale = (NSEC_PER_MSEC << NS_SCALE) / khz; -} + unsigned long flags, prev_scale, *scale; + unsigned long long tsc_now, ns_now; -static unsigned long long cycles_2_ns(unsigned long long cyc) -{ - return (cyc * cyc2ns_scale) >> NS_SCALE; + local_irq_save(flags); + sched_clock_idle_sleep_event(); + + scale = &per_cpu(cyc2ns, cpu); + + rdtscll(tsc_now); + ns_now = __cycles_2_ns(tsc_now); + + prev_scale = *scale; + if (cpu_khz) + *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz; + + sched_clock_idle_wakeup_event(0); + local_irq_restore(flags); } unsigned long long sched_clock(void) @@ -100,7 +133,9 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, mark_tsc_unstable("cpufreq changes"); } - set_cyc2ns_scale(tsc_khz_ref); + preempt_disable(); + set_cyc2ns_scale(tsc_khz_ref, smp_processor_id()); + preempt_enable(); return 0; } @@ -151,7 +186,7 @@ static unsigned long __init tsc_read_refs(unsigned long *pm, void __init tsc_calibrate(void) { unsigned long flags, tsc1, tsc2, tr1, tr2, pm1, pm2, hpet1, hpet2; - int hpet = is_hpet_enabled(); + int hpet = is_hpet_enabled(), cpu; local_irq_save(flags); @@ -206,7 +241,9 @@ void __init tsc_calibrate(void) } tsc_khz = tsc2 / tsc1; - set_cyc2ns_scale(tsc_khz); + + for_each_possible_cpu(cpu) + set_cyc2ns_scale(tsc_khz, cpu); } /* |