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Commit 53d517cd authored by Guillaume Chazarain's avatar Guillaume Chazarain Committed by Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 83bd0102

arch/x86/kernel/tsc_32.c

+37 −6
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <linux/jiffies.h>

#include <linux/init.h>

#include <linux/dmi.h>

#include <linux/percpu.h>



#include <asm/delay.h>

#include <asm/tsc.h>
@@ -80,13 +81,31 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable); 
 *

 *			-johnstul@us.ibm.com "math is hard, lets go shopping!"

 */

unsigned long cyc2ns_scale __read_mostly;



#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

DEFINE_PER_CPU(unsigned long, cyc2ns);



static inline void set_cyc2ns_scale(unsigned long cpu_khz)

static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)

{

	cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;

	unsigned long flags, prev_scale, *scale;

	unsigned long long tsc_now, ns_now;



	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;



	/*

	 * Start smoothly with the new frequency:

	 */

	sched_clock_idle_wakeup_event(0);

	local_irq_restore(flags);

}



/*
@@ -239,7 +258,9 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data) 
						ref_freq, freq->new);

			if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {

				tsc_khz = cpu_khz;

				set_cyc2ns_scale(cpu_khz);

				preempt_disable();

				set_cyc2ns_scale(cpu_khz, smp_processor_id());

				preempt_enable();

				/*

				 * TSC based sched_clock turns

				 * to junk w/ cpufreq
@@ -367,6 +388,8 @@ static inline void check_geode_tsc_reliable(void) { } 


void __init tsc_init(void)

{

	int cpu;



	if (!cpu_has_tsc || tsc_disable)

		goto out_no_tsc;
@@ -380,7 +403,15 @@ void __init tsc_init(void) 
				(unsigned long)cpu_khz / 1000,

				(unsigned long)cpu_khz % 1000);



	set_cyc2ns_scale(cpu_khz);

	/*

	 * Secondary CPUs do not run through tsc_init(), so set up

	 * all the scale factors for all CPUs, assuming the same

	 * speed as the bootup CPU. (cpufreq notifiers will fix this

	 * up if their speed diverges)

	 */

	for_each_possible_cpu(cpu)

		set_cyc2ns_scale(cpu_khz, cpu);



	use_tsc_delay();



	/* Check and install the TSC clocksource */

arch/x86/kernel/tsc_64.c

+47 −10
Original line number Diff line number Diff line
@@ -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);

}



/*

include/asm-x86/timer.h

+18 −5
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#define _ASMi386_TIMER_H

#include <linux/init.h>

#include <linux/pm.h>

#include <linux/percpu.h>



#define TICK_SIZE (tick_nsec / 1000)
@@ -16,7 +17,7 @@ extern int recalibrate_cpu_khz(void); 
#define calculate_cpu_khz() native_calculate_cpu_khz()

#endif



/* Accellerators for sched_clock()

/* Accelerators for sched_clock()

 * convert from cycles(64bits) => nanoseconds (64bits)

 *  basic equation:

 *		ns = cycles / (freq / ns_per_sec)
@@ -31,20 +32,32 @@ extern int recalibrate_cpu_khz(void); 
 *	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 percision, since

 *  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!"

 */

extern unsigned long cyc2ns_scale __read_mostly;



DECLARE_PER_CPU(unsigned long, cyc2ns);



#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */



static inline unsigned long long cycles_2_ns(unsigned long long cyc)

static inline unsigned long long __cycles_2_ns(unsigned long long cyc)

{

	return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;

	return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;

}



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