arch/x86_64/kernel/tsc.c

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/clocksource.h>
#include <linux/time.h>
#include <linux/acpi.h>
#include <linux/cpufreq.h>

#include <asm/timex.h>

static int notsc __initdata = 0;

unsigned int cpu_khz;		/* TSC clocks / usec, not used here */
EXPORT_SYMBOL(cpu_khz);
unsigned int tsc_khz;
EXPORT_SYMBOL(tsc_khz);

static unsigned int cyc2ns_scale __read_mostly;

void set_cyc2ns_scale(unsigned long khz)
{
	cyc2ns_scale = (NSEC_PER_MSEC << NS_SCALE) / khz;
}

static unsigned long long cycles_2_ns(unsigned long long cyc)
{
	return (cyc * cyc2ns_scale) >> NS_SCALE;
}

unsigned long long sched_clock(void)
{
	unsigned long a = 0;

	/* Could do CPU core sync here. Opteron can execute rdtsc speculatively,
	 * which means it is not completely exact and may not be monotonous
	 * between CPUs. But the errors should be too small to matter for
	 * scheduling purposes.
	 */

	rdtscll(a);
	return cycles_2_ns(a);
}

static int tsc_unstable;

inline int check_tsc_unstable(void)
{
	return tsc_unstable;
}
#ifdef CONFIG_CPU_FREQ

/* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
 * changes.
 *
 * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
 * not that important because current Opteron setups do not support
 * scaling on SMP anyroads.
 *
 * Should fix up last_tsc too. Currently gettimeofday in the
 * first tick after the change will be slightly wrong.
 */

static unsigned int  ref_freq;
static unsigned long loops_per_jiffy_ref;
static unsigned long tsc_khz_ref;

static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
				 void *data)
{
	struct cpufreq_freqs *freq = data;
	unsigned long *lpj, dummy;

	if (cpu_has(&cpu_data[freq->cpu], X86_FEATURE_CONSTANT_TSC))
		return 0;

	lpj = &dummy;
	if (!(freq->flags & CPUFREQ_CONST_LOOPS))
#ifdef CONFIG_SMP
		lpj = &cpu_data[freq->cpu].loops_per_jiffy;
#else
		lpj = &boot_cpu_data.loops_per_jiffy;
#endif

	if (!ref_freq) {
		ref_freq = freq->old;
		loops_per_jiffy_ref = *lpj;
		tsc_khz_ref = tsc_khz;
	}
	if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
		(val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
		(val == CPUFREQ_RESUMECHANGE)) {
		*lpj =
		cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);

		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
			mark_tsc_unstable("cpufreq changes");
	}

	set_cyc2ns_scale(tsc_khz_ref);

	return 0;
}

static struct notifier_block time_cpufreq_notifier_block = {
	.notifier_call  = time_cpufreq_notifier
};

static int __init cpufreq_tsc(void)
{
	cpufreq_register_notifier(&time_cpufreq_notifier_block,
				  CPUFREQ_TRANSITION_NOTIFIER);
	return 0;
}

core_initcall(cpufreq_tsc);

#endif

static int tsc_unstable = 0;

/*
 * Make an educated guess if the TSC is trustworthy and synchronized
 * over all CPUs.
 */
__cpuinit int unsynchronized_tsc(void)
{
	if (tsc_unstable)
		return 1;

#ifdef CONFIG_SMP
	if (apic_is_clustered_box())
		return 1;
#endif
	/* Most intel systems have synchronized TSCs except for
	   multi node systems */
	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
#ifdef CONFIG_ACPI
		/* But TSC doesn't tick in C3 so don't use it there */
		if (acpi_gbl_FADT.header.length > 0 &&
		    acpi_gbl_FADT.C3latency < 1000)
			return 1;
#endif
		return 0;
	}

	/* Assume multi socket systems are not synchronized */
	return num_present_cpus() > 1;
}

int __init notsc_setup(char *s)
{
	notsc = 1;
	return 1;
}

__setup("notsc", notsc_setup);


/* clock source code: */
static cycle_t read_tsc(void)
{
	cycle_t ret = (cycle_t)get_cycles_sync();
	return ret;
}

static cycle_t __vsyscall_fn vread_tsc(void)
{
	cycle_t ret = (cycle_t)get_cycles_sync();
	return ret;
}

static struct clocksource clocksource_tsc = {
	.name			= "tsc",
	.rating			= 300,
	.read			= read_tsc,
	.mask			= CLOCKSOURCE_MASK(64),
	.shift			= 22,
	.flags			= CLOCK_SOURCE_IS_CONTINUOUS |
				  CLOCK_SOURCE_MUST_VERIFY,
	.vread			= vread_tsc,
};

void mark_tsc_unstable(char *reason)
{
	if (!tsc_unstable) {
		tsc_unstable = 1;
		printk("Marking TSC unstable due to %s\n", reason);
		/* Change only the rating, when not registered */
		if (clocksource_tsc.mult)
			clocksource_change_rating(&clocksource_tsc, 0);
		else
			clocksource_tsc.rating = 0;
	}
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);

void __init init_tsc_clocksource(void)
{
	if (!notsc) {
		clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
							clocksource_tsc.shift);
		if (check_tsc_unstable())
			clocksource_tsc.rating = 0;

		clocksource_register(&clocksource_tsc);
	}
}