[PATCH] disable lost tick compensation before TSCs are synced

[linux-2.6/sactl.git] / arch / i386 / kernel / timers / timer_tsc.c

/*
 * This code largely moved from arch/i386/kernel/time.c.
 * See comments there for proper credits.
 *
 * 2004-06-25    Jesper Juhl
 *      moved mark_offset_tsc below cpufreq_delayed_get to avoid gcc 3.4
 *      failing to inline.
 */

#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/errno.h>
#include <linux/cpufreq.h>
#include <linux/string.h>
#include <linux/jiffies.h>

#include <asm/timer.h>
#include <asm/io.h>
/* processor.h for distable_tsc flag */
#include <asm/processor.h>

#include "io_ports.h"
#include "mach_timer.h"

#include <asm/hpet.h>
#include <asm/i8253.h>

#ifdef CONFIG_HPET_TIMER
static unsigned long hpet_usec_quotient;
static unsigned long hpet_last;
static struct timer_opts timer_tsc;
#endif

static inline void cpufreq_delayed_get(void);

int tsc_disable __devinitdata = 0;

static int use_tsc;
/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;

static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
static unsigned long long monotonic_base;
static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;

/* Avoid compensating for lost ticks before TSCs are synched */
static int detect_lost_ticks;
static int __init start_lost_tick_compensation(void)
{
        detect_lost_ticks = 1;
        return 0;
}
late_initcall(start_lost_tick_compensation);

/* 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 percision, 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!"
 */
static unsigned long cyc2ns_scale; 
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline void set_cyc2ns_scale(unsigned long cpu_khz)
{
        cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
}

static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
        return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
}

static int count2; /* counter for mark_offset_tsc() */

/* Cached *multiplier* to convert TSC counts to microseconds.
 * (see the equation below).
 * Equal to 2^32 * (1 / (clocks per usec) ).
 * Initialized in time_init.
 */
static unsigned long fast_gettimeoffset_quotient;

static unsigned long get_offset_tsc(void)
{
        register unsigned long eax, edx;

        /* Read the Time Stamp Counter */

        rdtsc(eax,edx);

        /* .. relative to previous jiffy (32 bits is enough) */
        eax -= last_tsc_low;    /* tsc_low delta */

        /*
         * Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
         *             = (tsc_low delta) * (usecs_per_clock)
         *             = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
         *
         * Using a mull instead of a divl saves up to 31 clock cycles
         * in the critical path.
         */

        __asm__("mull %2"
                :"=a" (eax), "=d" (edx)
                :"rm" (fast_gettimeoffset_quotient),
                 "0" (eax));

        /* our adjusted time offset in microseconds */
        return delay_at_last_interrupt + edx;
}

static unsigned long long monotonic_clock_tsc(void)
{
        unsigned long long last_offset, this_offset, base;
        unsigned seq;
        
        /* atomically read monotonic base & last_offset */
        do {
                seq = read_seqbegin(&monotonic_lock);
                last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
                base = monotonic_base;
        } while (read_seqretry(&monotonic_lock, seq));

        /* Read the Time Stamp Counter */
        rdtscll(this_offset);

        /* return the value in ns */
        return base + cycles_2_ns(this_offset - last_offset);
}

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

        /*
         * In the NUMA case we dont use the TSC as they are not
         * synchronized across all CPUs.
         */
#ifndef CONFIG_NUMA
        if (!use_tsc)
#endif
                /* no locking but a rare wrong value is not a big deal */
                return jiffies_64 * (1000000000 / HZ);

        /* Read the Time Stamp Counter */
        rdtscll(this_offset);

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

static void delay_tsc(unsigned long loops)
{
        unsigned long bclock, now;
        
        rdtscl(bclock);
        do
        {
                rep_nop();
                rdtscl(now);
        } while ((now-bclock) < loops);
}

#ifdef CONFIG_HPET_TIMER
static void mark_offset_tsc_hpet(void)
{
        unsigned long long this_offset, last_offset;
        unsigned long offset, temp, hpet_current;

        write_seqlock(&monotonic_lock);
        last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
        /*
         * It is important that these two operations happen almost at
         * the same time. We do the RDTSC stuff first, since it's
         * faster. To avoid any inconsistencies, we need interrupts
         * disabled locally.
         */
        /*
         * Interrupts are just disabled locally since the timer irq
         * has the SA_INTERRUPT flag set. -arca
         */
        /* read Pentium cycle counter */

        hpet_current = hpet_readl(HPET_COUNTER);
        rdtsc(last_tsc_low, last_tsc_high);

        /* lost tick compensation */
        offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
        if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))
                                        && detect_lost_ticks) {
                int lost_ticks = (offset - hpet_last) / hpet_tick;
                jiffies_64 += lost_ticks;
        }
        hpet_last = hpet_current;

        /* update the monotonic base value */
        this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
        monotonic_base += cycles_2_ns(this_offset - last_offset);
        write_sequnlock(&monotonic_lock);

        /* calculate delay_at_last_interrupt */
        /*
         * Time offset = (hpet delta) * ( usecs per HPET clock )
         *             = (hpet delta) * ( usecs per tick / HPET clocks per tick)
         *             = (hpet delta) * ( hpet_usec_quotient ) / (2^32)
         * Where,
         * hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
         */
        delay_at_last_interrupt = hpet_current - offset;
        ASM_MUL64_REG(temp, delay_at_last_interrupt,
                        hpet_usec_quotient, delay_at_last_interrupt);
}
#endif


#ifdef CONFIG_CPU_FREQ
#include <linux/workqueue.h>

static unsigned int cpufreq_delayed_issched = 0;
static unsigned int cpufreq_init = 0;
static struct work_struct cpufreq_delayed_get_work;

static void handle_cpufreq_delayed_get(void *v)
{
        unsigned int cpu;
        for_each_online_cpu(cpu) {
                cpufreq_get(cpu);
        }
        cpufreq_delayed_issched = 0;
}

/* if we notice lost ticks, schedule a call to cpufreq_get() as it tries
 * to verify the CPU frequency the timing core thinks the CPU is running
 * at is still correct.
 */
static inline void cpufreq_delayed_get(void) 
{
        if (cpufreq_init && !cpufreq_delayed_issched) {
                cpufreq_delayed_issched = 1;
                printk(KERN_DEBUG "Losing some ticks... checking if CPU frequency changed.\n");
                schedule_work(&cpufreq_delayed_get_work);
        }
}

/* 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;

#ifndef CONFIG_SMP
static unsigned long fast_gettimeoffset_ref = 0;
static unsigned int cpu_khz_ref = 0;
#endif

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

        if (val != CPUFREQ_RESUMECHANGE)
                write_seqlock_irq(&xtime_lock);
        if (!ref_freq) {
                ref_freq = freq->old;
                loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
#ifndef CONFIG_SMP
                fast_gettimeoffset_ref = fast_gettimeoffset_quotient;
                cpu_khz_ref = cpu_khz;
#endif
        }

        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);
#ifndef CONFIG_SMP
                if (cpu_khz)
                        cpu_khz = cpufreq_scale(cpu_khz_ref, ref_freq, freq->new);
                if (use_tsc) {
                        if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
                                fast_gettimeoffset_quotient = cpufreq_scale(fast_gettimeoffset_ref, freq->new, ref_freq);
                                set_cyc2ns_scale(cpu_khz);
                        }
                }
#endif
        }

        if (val != CPUFREQ_RESUMECHANGE)
                write_sequnlock_irq(&xtime_lock);

        return 0;
}

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


static int __init cpufreq_tsc(void)
{
        int ret;
        INIT_WORK(&cpufreq_delayed_get_work, handle_cpufreq_delayed_get, NULL);
        ret = cpufreq_register_notifier(&time_cpufreq_notifier_block,
                                        CPUFREQ_TRANSITION_NOTIFIER);
        if (!ret)
                cpufreq_init = 1;
        return ret;
}
core_initcall(cpufreq_tsc);

#else /* CONFIG_CPU_FREQ */
static inline void cpufreq_delayed_get(void) { return; }
#endif 

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

        if (cpu_has_tsc) {
                local_irq_disable();
                init_cpu_khz();
                local_irq_enable();
                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);

static void mark_offset_tsc(void)
{
        unsigned long lost,delay;
        unsigned long delta = last_tsc_low;
        int count;
        int countmp;
        static int count1 = 0;
        unsigned long long this_offset, last_offset;
        static int lost_count = 0;

        write_seqlock(&monotonic_lock);
        last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
        /*
         * It is important that these two operations happen almost at
         * the same time. We do the RDTSC stuff first, since it's
         * faster. To avoid any inconsistencies, we need interrupts
         * disabled locally.
         */

        /*
         * Interrupts are just disabled locally since the timer irq
         * has the SA_INTERRUPT flag set. -arca
         */

        /* read Pentium cycle counter */

        rdtsc(last_tsc_low, last_tsc_high);

        spin_lock(&i8253_lock);
        outb_p(0x00, PIT_MODE);     /* latch the count ASAP */

        count = inb_p(PIT_CH0);    /* read the latched count */
        count |= inb(PIT_CH0) << 8;

        /*
         * VIA686a test code... reset the latch if count > max + 1
         * from timer_pit.c - cjb
         */
        if (count > LATCH) {
                outb_p(0x34, PIT_MODE);
                outb_p(LATCH & 0xff, PIT_CH0);
                outb(LATCH >> 8, PIT_CH0);
                count = LATCH - 1;
        }

        spin_unlock(&i8253_lock);

        if (pit_latch_buggy) {
                /* get center value of last 3 time lutch */
                if ((count2 >= count && count >= count1)
                    || (count1 >= count && count >= count2)) {
                        count2 = count1; count1 = count;
                } else if ((count1 >= count2 && count2 >= count)
                           || (count >= count2 && count2 >= count1)) {
                        countmp = count;count = count2;
                        count2 = count1;count1 = countmp;
                } else {
                        count2 = count1; count1 = count; count = count1;
                }
        }

        /* lost tick compensation */
        delta = last_tsc_low - delta;
        {
                register unsigned long eax, edx;
                eax = delta;
                __asm__("mull %2"
                :"=a" (eax), "=d" (edx)
                :"rm" (fast_gettimeoffset_quotient),
                 "0" (eax));
                delta = edx;
        }
        delta += delay_at_last_interrupt;
        lost = delta/(1000000/HZ);
        delay = delta%(1000000/HZ);
        if (lost >= 2 && detect_lost_ticks) {
                jiffies_64 += lost-1;

                /* sanity check to ensure we're not always losing ticks */
                if (lost_count++ > 100) {
                        printk(KERN_WARNING "Losing too many ticks!\n");
                        printk(KERN_WARNING "TSC cannot be used as a timesource.  \n");
                        printk(KERN_WARNING "Possible reasons for this are:\n");
                        printk(KERN_WARNING "  You're running with Speedstep,\n");
                        printk(KERN_WARNING "  You don't have DMA enabled for your hard disk (see hdparm),\n");
                        printk(KERN_WARNING "  Incorrect TSC synchronization on an SMP system (see dmesg).\n");
                        printk(KERN_WARNING "Falling back to a sane timesource now.\n");

                        clock_fallback();
                }
                /* ... but give the TSC a fair chance */
                if (lost_count > 25)
                        cpufreq_delayed_get();
        } else
                lost_count = 0;
        /* update the monotonic base value */
        this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
        monotonic_base += cycles_2_ns(this_offset - last_offset);
        write_sequnlock(&monotonic_lock);

        /* calculate delay_at_last_interrupt */
        count = ((LATCH-1) - count) * TICK_SIZE;
        delay_at_last_interrupt = (count + LATCH/2) / LATCH;

        /* catch corner case where tick rollover occured
         * between tsc and pit reads (as noted when
         * usec delta is > 90% # of usecs/tick)
         */
        if (lost && abs(delay - delay_at_last_interrupt) > (900000/HZ))
                jiffies_64++;
}

static int __init init_tsc(char* override)
{

        /* check clock override */
        if (override[0] && strncmp(override,"tsc",3)) {
#ifdef CONFIG_HPET_TIMER
                if (is_hpet_enabled()) {
                        printk(KERN_ERR "Warning: clock= override failed. Defaulting to tsc\n");
                } else
#endif
                {
                        return -ENODEV;
                }
        }

        /*
         * If we have APM enabled or the CPU clock speed is variable
         * (CPU stops clock on HLT or slows clock to save power)
         * then the TSC timestamps may diverge by up to 1 jiffy from
         * 'real time' but nothing will break.
         * The most frequent case is that the CPU is "woken" from a halt
         * state by the timer interrupt itself, so we get 0 error. In the
         * rare cases where a driver would "wake" the CPU and request a
         * timestamp, the maximum error is < 1 jiffy. But timestamps are
         * still perfectly ordered.
         * Note that the TSC counter will be reset if APM suspends
         * to disk; this won't break the kernel, though, 'cuz we're
         * smart.  See arch/i386/kernel/apm.c.
         */
        /*
         *      Firstly we have to do a CPU check for chips with
         *      a potentially buggy TSC. At this point we haven't run
         *      the ident/bugs checks so we must run this hook as it
         *      may turn off the TSC flag.
         *
         *      NOTE: this doesn't yet handle SMP 486 machines where only
         *      some CPU's have a TSC. Thats never worked and nobody has
         *      moaned if you have the only one in the world - you fix it!
         */

        count2 = LATCH; /* initialize counter for mark_offset_tsc() */

        if (cpu_has_tsc) {
                unsigned long tsc_quotient;
#ifdef CONFIG_HPET_TIMER
                if (is_hpet_enabled() && hpet_use_timer) {
                        unsigned long result, remain;
                        printk("Using TSC for gettimeofday\n");
                        tsc_quotient = calibrate_tsc_hpet(NULL);
                        timer_tsc.mark_offset = &mark_offset_tsc_hpet;
                        /*
                         * Math to calculate hpet to usec multiplier
                         * Look for the comments at get_offset_tsc_hpet()
                         */
                        ASM_DIV64_REG(result, remain, hpet_tick,
                                        0, KERNEL_TICK_USEC);
                        if (remain > (hpet_tick >> 1))
                                result++; /* rounding the result */

                        hpet_usec_quotient = result;
                } else
#endif
                {
                        tsc_quotient = calibrate_tsc();
                }

                if (tsc_quotient) {
                        fast_gettimeoffset_quotient = tsc_quotient;
                        use_tsc = 1;
                        /*
                         *      We could be more selective here I suspect
                         *      and just enable this for the next intel chips ?
                         */
                        /* report CPU clock rate in Hz.
                         * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
                         * clock/second. Our precision is about 100 ppm.
                         */
                        {       unsigned long eax=0, edx=1000;
                                __asm__("divl %2"
                                :"=a" (cpu_khz), "=d" (edx)
                                :"r" (tsc_quotient),
                                "0" (eax), "1" (edx));
                                printk("Detected %u.%03u MHz processor.\n",
                                        cpu_khz / 1000, cpu_khz % 1000);
                        }
                        set_cyc2ns_scale(cpu_khz);
                        return 0;
                }
        }
        return -ENODEV;
}

static int tsc_resume(void)
{
        write_seqlock(&monotonic_lock);
        /* Assume this is the last mark offset time */
        rdtsc(last_tsc_low, last_tsc_high);
#ifdef CONFIG_HPET_TIMER
        if (is_hpet_enabled() && hpet_use_timer)
                hpet_last = hpet_readl(HPET_COUNTER);
#endif
        write_sequnlock(&monotonic_lock);
        return 0;
}

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



/************************************************************/

/* tsc timer_opts struct */
static struct timer_opts timer_tsc = {
        .name = "tsc",
        .mark_offset = mark_offset_tsc, 
        .get_offset = get_offset_tsc,
        .monotonic_clock = monotonic_clock_tsc,
        .delay = delay_tsc,
        .read_timer = read_timer_tsc,
        .resume = tsc_resume,
};

struct init_timer_opts __initdata timer_tsc_init = {
        .init = init_tsc,
        .opts = &timer_tsc,
};