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

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
...@@ -5,6 +5,7 @@ ...@@ -5,6 +5,7 @@
#include <linux/jiffies.h> #include <linux/jiffies.h>
#include <linux/init.h> #include <linux/init.h>
#include <linux/dmi.h> #include <linux/dmi.h>
#include <linux/percpu.h>
#include <asm/delay.h> #include <asm/delay.h>
#include <asm/tsc.h> #include <asm/tsc.h>
...@@ -80,13 +81,31 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable); ...@@ -80,13 +81,31 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable);
* *
* -johnstul@us.ibm.com "math is hard, lets go shopping!" * -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) ...@@ -239,7 +258,9 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
ref_freq, freq->new); ref_freq, freq->new);
if (!(freq->flags & CPUFREQ_CONST_LOOPS)) { if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
tsc_khz = cpu_khz; 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 * TSC based sched_clock turns
* to junk w/ cpufreq * to junk w/ cpufreq
...@@ -367,6 +388,8 @@ static inline void check_geode_tsc_reliable(void) { } ...@@ -367,6 +388,8 @@ static inline void check_geode_tsc_reliable(void) { }
void __init tsc_init(void) void __init tsc_init(void)
{ {
int cpu;
if (!cpu_has_tsc || tsc_disable) if (!cpu_has_tsc || tsc_disable)
goto out_no_tsc; goto out_no_tsc;
...@@ -380,7 +403,15 @@ void __init tsc_init(void) ...@@ -380,7 +403,15 @@ void __init tsc_init(void)
(unsigned long)cpu_khz / 1000, (unsigned long)cpu_khz / 1000,
(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(); use_tsc_delay();
/* Check and install the TSC clocksource */ /* Check and install the TSC clocksource */
......
...@@ -10,6 +10,7 @@ ...@@ -10,6 +10,7 @@
#include <asm/hpet.h> #include <asm/hpet.h>
#include <asm/timex.h> #include <asm/timex.h>
#include <asm/timer.h>
static int notsc __initdata = 0; static int notsc __initdata = 0;
...@@ -18,16 +19,48 @@ EXPORT_SYMBOL(cpu_khz); ...@@ -18,16 +19,48 @@ EXPORT_SYMBOL(cpu_khz);
unsigned int tsc_khz; unsigned int tsc_khz;
EXPORT_SYMBOL(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) local_irq_save(flags);
{ sched_clock_idle_sleep_event();
return (cyc * cyc2ns_scale) >> NS_SCALE;
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) unsigned long long sched_clock(void)
...@@ -100,7 +133,9 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, ...@@ -100,7 +133,9 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
mark_tsc_unstable("cpufreq changes"); 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; return 0;
} }
...@@ -151,7 +186,7 @@ static unsigned long __init tsc_read_refs(unsigned long *pm, ...@@ -151,7 +186,7 @@ static unsigned long __init tsc_read_refs(unsigned long *pm,
void __init tsc_calibrate(void) void __init tsc_calibrate(void)
{ {
unsigned long flags, tsc1, tsc2, tr1, tr2, pm1, pm2, hpet1, hpet2; 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); local_irq_save(flags);
...@@ -206,7 +241,9 @@ void __init tsc_calibrate(void) ...@@ -206,7 +241,9 @@ void __init tsc_calibrate(void)
} }
tsc_khz = tsc2 / tsc1; tsc_khz = tsc2 / tsc1;
set_cyc2ns_scale(tsc_khz);
for_each_possible_cpu(cpu)
set_cyc2ns_scale(tsc_khz, cpu);
} }
/* /*
......
...@@ -2,6 +2,7 @@ ...@@ -2,6 +2,7 @@
#define _ASMi386_TIMER_H #define _ASMi386_TIMER_H
#include <linux/init.h> #include <linux/init.h>
#include <linux/pm.h> #include <linux/pm.h>
#include <linux/percpu.h>
#define TICK_SIZE (tick_nsec / 1000) #define TICK_SIZE (tick_nsec / 1000)
...@@ -16,7 +17,7 @@ extern int recalibrate_cpu_khz(void); ...@@ -16,7 +17,7 @@ extern int recalibrate_cpu_khz(void);
#define calculate_cpu_khz() native_calculate_cpu_khz() #define calculate_cpu_khz() native_calculate_cpu_khz()
#endif #endif
/* Accellerators for sched_clock() /* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits) * convert from cycles(64bits) => nanoseconds (64bits)
* basic equation: * basic equation:
* ns = cycles / (freq / ns_per_sec) * ns = cycles / (freq / ns_per_sec)
...@@ -31,20 +32,32 @@ extern int recalibrate_cpu_khz(void); ...@@ -31,20 +32,32 @@ extern int recalibrate_cpu_khz(void);
* And since SC is a constant power of two, we can convert the div * And since SC is a constant power of two, we can convert the div
* into a shift. * 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. * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca) * (mathieu.desnoyers@polymtl.ca)
* *
* -johnstul@us.ibm.com "math is hard, lets go shopping!" * -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 */ #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 #endif
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