x86: scale cyc_2_nsec according to CPU frequency
scale the sched_clock() cyc_2_nsec scaling factor according to CPU frequency changes. [ mingo@elte.hu: simplified it and fixed it for SMP. ] Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Guillaume Chazarain
Ingo Molnar
parent
83bd01024b
commit
53d517cdba
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@ -5,6 +5,7 @@
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#include <linux/jiffies.h>
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#include <linux/init.h>
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#include <linux/dmi.h>
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#include <linux/percpu.h>
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#include <asm/delay.h>
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#include <asm/tsc.h>
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@ -80,13 +81,31 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable);
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*
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* -johnstul@us.ibm.com "math is hard, lets go shopping!"
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*/
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unsigned long cyc2ns_scale __read_mostly;
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#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
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DEFINE_PER_CPU(unsigned long, cyc2ns);
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static inline void set_cyc2ns_scale(unsigned long cpu_khz)
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static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
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{
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cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
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unsigned long flags, prev_scale, *scale;
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unsigned long long tsc_now, ns_now;
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local_irq_save(flags);
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sched_clock_idle_sleep_event();
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scale = &per_cpu(cyc2ns, cpu);
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rdtscll(tsc_now);
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ns_now = __cycles_2_ns(tsc_now);
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prev_scale = *scale;
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if (cpu_khz)
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*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
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/*
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* Start smoothly with the new frequency:
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*/
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sched_clock_idle_wakeup_event(0);
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local_irq_restore(flags);
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}
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/*
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@ -239,7 +258,9 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
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ref_freq, freq->new);
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if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
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tsc_khz = cpu_khz;
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set_cyc2ns_scale(cpu_khz);
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preempt_disable();
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set_cyc2ns_scale(cpu_khz, smp_processor_id());
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preempt_enable();
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/*
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* TSC based sched_clock turns
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* to junk w/ cpufreq
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@ -367,6 +388,8 @@ static inline void check_geode_tsc_reliable(void) { }
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void __init tsc_init(void)
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{
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int cpu;
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if (!cpu_has_tsc || tsc_disable)
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goto out_no_tsc;
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@ -380,7 +403,15 @@ void __init tsc_init(void)
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(unsigned long)cpu_khz / 1000,
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(unsigned long)cpu_khz % 1000);
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set_cyc2ns_scale(cpu_khz);
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/*
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* Secondary CPUs do not run through tsc_init(), so set up
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* all the scale factors for all CPUs, assuming the same
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* speed as the bootup CPU. (cpufreq notifiers will fix this
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* up if their speed diverges)
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*/
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for_each_possible_cpu(cpu)
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set_cyc2ns_scale(cpu_khz, cpu);
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use_tsc_delay();
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/* Check and install the TSC clocksource */
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@ -10,6 +10,7 @@
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#include <asm/hpet.h>
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#include <asm/timex.h>
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#include <asm/timer.h>
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static int notsc __initdata = 0;
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@ -18,16 +19,48 @@ EXPORT_SYMBOL(cpu_khz);
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unsigned int tsc_khz;
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EXPORT_SYMBOL(tsc_khz);
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static unsigned int cyc2ns_scale __read_mostly;
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/* Accelerators for sched_clock()
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* convert from cycles(64bits) => nanoseconds (64bits)
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* basic equation:
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* ns = cycles / (freq / ns_per_sec)
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* ns = cycles * (ns_per_sec / freq)
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* ns = cycles * (10^9 / (cpu_khz * 10^3))
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* ns = cycles * (10^6 / cpu_khz)
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*
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* Then we use scaling math (suggested by george@mvista.com) to get:
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* ns = cycles * (10^6 * SC / cpu_khz) / SC
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* ns = cycles * cyc2ns_scale / SC
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*
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* And since SC is a constant power of two, we can convert the div
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* into a shift.
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*
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* We can use khz divisor instead of mhz to keep a better precision, since
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* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
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* (mathieu.desnoyers@polymtl.ca)
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*
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* -johnstul@us.ibm.com "math is hard, lets go shopping!"
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*/
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DEFINE_PER_CPU(unsigned long, cyc2ns);
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static inline void set_cyc2ns_scale(unsigned long khz)
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static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
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{
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cyc2ns_scale = (NSEC_PER_MSEC << NS_SCALE) / khz;
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}
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unsigned long flags, prev_scale, *scale;
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unsigned long long tsc_now, ns_now;
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static unsigned long long cycles_2_ns(unsigned long long cyc)
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{
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return (cyc * cyc2ns_scale) >> NS_SCALE;
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local_irq_save(flags);
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sched_clock_idle_sleep_event();
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scale = &per_cpu(cyc2ns, cpu);
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rdtscll(tsc_now);
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ns_now = __cycles_2_ns(tsc_now);
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prev_scale = *scale;
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if (cpu_khz)
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*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
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sched_clock_idle_wakeup_event(0);
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local_irq_restore(flags);
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}
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unsigned long long sched_clock(void)
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@ -100,7 +133,9 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
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mark_tsc_unstable("cpufreq changes");
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}
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set_cyc2ns_scale(tsc_khz_ref);
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preempt_disable();
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set_cyc2ns_scale(tsc_khz_ref, smp_processor_id());
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preempt_enable();
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return 0;
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}
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@ -151,7 +186,7 @@ static unsigned long __init tsc_read_refs(unsigned long *pm,
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void __init tsc_calibrate(void)
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{
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unsigned long flags, tsc1, tsc2, tr1, tr2, pm1, pm2, hpet1, hpet2;
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int hpet = is_hpet_enabled();
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int hpet = is_hpet_enabled(), cpu;
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local_irq_save(flags);
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@ -206,7 +241,9 @@ void __init tsc_calibrate(void)
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}
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tsc_khz = tsc2 / tsc1;
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set_cyc2ns_scale(tsc_khz);
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for_each_possible_cpu(cpu)
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set_cyc2ns_scale(tsc_khz, cpu);
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}
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/*
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@ -2,6 +2,7 @@
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#define _ASMi386_TIMER_H
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#include <linux/init.h>
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#include <linux/pm.h>
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#include <linux/percpu.h>
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#define TICK_SIZE (tick_nsec / 1000)
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@ -16,7 +17,7 @@ extern int recalibrate_cpu_khz(void);
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#define calculate_cpu_khz() native_calculate_cpu_khz()
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#endif
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/* Accellerators for sched_clock()
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/* Accelerators for sched_clock()
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* convert from cycles(64bits) => nanoseconds (64bits)
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* basic equation:
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* ns = cycles / (freq / ns_per_sec)
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@ -31,20 +32,32 @@ extern int recalibrate_cpu_khz(void);
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* And since SC is a constant power of two, we can convert the div
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* into a shift.
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*
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* We can use khz divisor instead of mhz to keep a better percision, since
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* We can use khz divisor instead of mhz to keep a better precision, since
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* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
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* (mathieu.desnoyers@polymtl.ca)
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*
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* -johnstul@us.ibm.com "math is hard, lets go shopping!"
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*/
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extern unsigned long cyc2ns_scale __read_mostly;
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DECLARE_PER_CPU(unsigned long, cyc2ns);
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#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
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static inline unsigned long long cycles_2_ns(unsigned long long cyc)
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static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
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{
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return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
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return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;
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}
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static inline unsigned long long cycles_2_ns(unsigned long long cyc)
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{
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unsigned long long ns;
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unsigned long flags;
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local_irq_save(flags);
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ns = __cycles_2_ns(cyc);
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local_irq_restore(flags);
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return ns;
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}
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#endif
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