sched: make early bootup sched_clock() use safer

[wrt350n-kernel.git] / arch / x86 / kernel / tsc_32.c

#include <linux/sched.h>
#include <linux/clocksource.h>
#include <linux/workqueue.h>
#include <linux/cpufreq.h>
#include <linux/jiffies.h>
#include <linux/init.h>
#include <linux/dmi.h>
#include <linux/percpu.h>

#include <asm/delay.h>
#include <asm/tsc.h>
#include <asm/io.h>
#include <asm/timer.h>

#include "mach_timer.h"

static int tsc_enabled;

/*
 * On some systems the TSC frequency does not
 * change with the cpu frequency. So we need
 * an extra value to store the TSC freq
 */
unsigned int tsc_khz;
EXPORT_SYMBOL_GPL(tsc_khz);

#ifdef CONFIG_X86_TSC
static int __init tsc_setup(char *str)
{
        printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
                                "cannot disable TSC.\n");
        return 1;
}
#else
/*
 * disable flag for tsc. Takes effect by clearing the TSC cpu flag
 * in cpu/common.c
 */
static int __init tsc_setup(char *str)
{
        setup_clear_cpu_cap(X86_FEATURE_TSC);
        return 1;
}
#endif

__setup("notsc", tsc_setup);

/*
 * code to mark and check if the TSC is unstable
 * due to cpufreq or due to unsynced TSCs
 */
static int tsc_unstable;

int check_tsc_unstable(void)
{
        return tsc_unstable;
}
EXPORT_SYMBOL_GPL(check_tsc_unstable);

/* 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 void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
{
        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);
}

/*
 * Scheduler clock - returns current time in nanosec units.
 */
unsigned long long native_sched_clock(void)
{
        unsigned long long this_offset;

        /*
         * Fall back to jiffies if there's no TSC available:
         * ( But note that we still use it if the TSC is marked
         *   unstable. We do this because unlike Time Of Day,
         *   the scheduler clock tolerates small errors and it's
         *   very important for it to be as fast as the platform
         *   can achive it. )
         */
        if (unlikely(!tsc_enabled && !tsc_unstable))
                /* No locking but a rare wrong value is not a big deal: */
                return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

        /* read the Time Stamp Counter: */
        rdtscll(this_offset);

        /* return the value in ns */
        return cycles_2_ns(this_offset);
}

/* We need to define a real function for sched_clock, to override the
   weak default version */
#ifdef CONFIG_PARAVIRT
unsigned long long sched_clock(void)
{
        return paravirt_sched_clock();
}
#else
unsigned long long sched_clock(void)
        __attribute__((alias("native_sched_clock")));
#endif

unsigned long native_calculate_cpu_khz(void)
{
        unsigned long long start, end;
        unsigned long count;
        u64 delta64 = (u64)ULLONG_MAX;
        int i;
        unsigned long flags;

        local_irq_save(flags);

        /* run 3 times to ensure the cache is warm and to get an accurate reading */
        for (i = 0; i < 3; i++) {
                mach_prepare_counter();
                rdtscll(start);
                mach_countup(&count);
                rdtscll(end);

                /*
                 * Error: ECTCNEVERSET
                 * The CTC wasn't reliable: we got a hit on the very first read,
                 * or the CPU was so fast/slow that the quotient wouldn't fit in
                 * 32 bits..
                 */
                if (count <= 1)
                        continue;

                /* cpu freq too slow: */
                if ((end - start) <= CALIBRATE_TIME_MSEC)
                        continue;

                /*
                 * We want the minimum time of all runs in case one of them
                 * is inaccurate due to SMI or other delay
                 */
                delta64 = min(delta64, (end - start));
        }

        /* cpu freq too fast (or every run was bad): */
        if (delta64 > (1ULL<<32))
                goto err;

        delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
        do_div(delta64,CALIBRATE_TIME_MSEC);

        local_irq_restore(flags);
        return (unsigned long)delta64;
err:
        local_irq_restore(flags);
        return 0;
}

int recalibrate_cpu_khz(void)
{
#ifndef CONFIG_SMP
        unsigned long cpu_khz_old = cpu_khz;

        if (cpu_has_tsc) {
                cpu_khz = calculate_cpu_khz();
                tsc_khz = cpu_khz;
                cpu_data(0).loops_per_jiffy =
                        cpufreq_scale(cpu_data(0).loops_per_jiffy,
                                        cpu_khz_old, cpu_khz);
                return 0;
        } else
                return -ENODEV;
#else
        return -ENODEV;
#endif
}

EXPORT_SYMBOL(recalibrate_cpu_khz);

#ifdef CONFIG_CPU_FREQ

/*
 * if the CPU frequency is scaled, TSC-based delays will need a different
 * loops_per_jiffy value to function properly.
 */
static unsigned int ref_freq = 0;
static unsigned long loops_per_jiffy_ref = 0;
static unsigned long cpu_khz_ref = 0;

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

        if (!ref_freq) {
                if (!freq->old){
                        ref_freq = freq->new;
                        return 0;
                }
                ref_freq = freq->old;
                loops_per_jiffy_ref = cpu_data(freq->cpu).loops_per_jiffy;
                cpu_khz_ref = cpu_khz;
        }

        if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
            (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
            (val == CPUFREQ_RESUMECHANGE)) {
                if (!(freq->flags & CPUFREQ_CONST_LOOPS))
                        cpu_data(freq->cpu).loops_per_jiffy =
                                cpufreq_scale(loops_per_jiffy_ref,
                                                ref_freq, freq->new);

                if (cpu_khz) {

                        if (num_online_cpus() == 1)
                                cpu_khz = cpufreq_scale(cpu_khz_ref,
                                                ref_freq, freq->new);
                        if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
                                tsc_khz = cpu_khz;
                                preempt_disable();
                                set_cyc2ns_scale(cpu_khz, smp_processor_id());
                                preempt_enable();
                                /*
                                 * TSC based sched_clock turns
                                 * to junk w/ cpufreq
                                 */
                                mark_tsc_unstable("cpufreq changes");
                        }
                }
        }

        return 0;
}

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

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

#endif

/* clock source code */

static unsigned long current_tsc_khz = 0;

static cycle_t read_tsc(void)
{
        cycle_t ret;

        rdtscll(ret);

        return ret;
}

static struct clocksource clocksource_tsc = {
        .name                   = "tsc",
        .rating                 = 300,
        .read                   = read_tsc,
        .mask                   = CLOCKSOURCE_MASK(64),
        .mult                   = 0, /* to be set */
        .shift                  = 22,
        .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
                                  CLOCK_SOURCE_MUST_VERIFY,
};

void mark_tsc_unstable(char *reason)
{
        if (!tsc_unstable) {
                tsc_unstable = 1;
                tsc_enabled = 0;
                printk("Marking TSC unstable due to: %s.\n", reason);
                /* Can be called before registration */
                if (clocksource_tsc.mult)
                        clocksource_change_rating(&clocksource_tsc, 0);
                else
                        clocksource_tsc.rating = 0;
        }
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);

static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d)
{
        printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
                       d->ident);
        tsc_unstable = 1;
        return 0;
}

/* List of systems that have known TSC problems */
static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
        {
         .callback = dmi_mark_tsc_unstable,
         .ident = "IBM Thinkpad 380XD",
         .matches = {
                     DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
                     DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
                     },
         },
         {}
};

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

        /* Anything with constant TSC should be synchronized */
        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
                return 0;

        /*
         * Intel systems are normally all synchronized.
         * Exceptions must mark TSC as unstable:
         */
        if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
                /* assume multi socket systems are not synchronized: */
                if (num_possible_cpus() > 1)
                        tsc_unstable = 1;
        }
        return tsc_unstable;
}

/*
 * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
 */
#ifdef CONFIG_MGEODE_LX
/* RTSC counts during suspend */
#define RTSC_SUSP 0x100

static void __init check_geode_tsc_reliable(void)
{
        unsigned long res_low, res_high;

        rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
        if (res_low & RTSC_SUSP)
                clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
}
#else
static inline void check_geode_tsc_reliable(void) { }
#endif


void __init tsc_init(void)
{
        int cpu;

        if (!cpu_has_tsc)
                goto out_no_tsc;

        cpu_khz = calculate_cpu_khz();
        tsc_khz = cpu_khz;

        if (!cpu_khz)
                goto out_no_tsc;

        printk("Detected %lu.%03lu MHz processor.\n",
                                (unsigned long)cpu_khz / 1000,
                                (unsigned long)cpu_khz % 1000);

        /*
         * 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 */
        dmi_check_system(bad_tsc_dmi_table);

        unsynchronized_tsc();
        check_geode_tsc_reliable();
        current_tsc_khz = tsc_khz;
        clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
                                                        clocksource_tsc.shift);
        /* lower the rating if we already know its unstable: */
        if (check_tsc_unstable()) {
                clocksource_tsc.rating = 0;
                clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
        } else
                tsc_enabled = 1;

        clocksource_register(&clocksource_tsc);

        return;

out_no_tsc:
        setup_clear_cpu_cap(X86_FEATURE_TSC);
}