[PATCH] clocksource: Add verification (watchdog) helper

The TSC needs to be verified against another clocksource.  Instead of using
hardwired assumptions of available hardware, provide a generic verification
mechanism.  The verification uses the best available clocksource and handles
the usability for high resolution timers / dynticks of the clocksource which
needs to be verified.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 161 insertions, 78 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 4ea31c327d1f..458b3aad3eb3 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -18,6 +18,10 @@ config GENERIC_TIME
         bool
         default y
 
+config CLOCKSOURCE_WATCHDOG
+        bool
+        default y
+
 config LOCKDEP_SUPPORT
         bool
         default y
diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index b4b2be21d1c7..22931d24027c 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -344,49 +344,6 @@ static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
          {}
 };
 
-#define TSC_FREQ_CHECK_INTERVAL (10*MSEC_PER_SEC) /* 10sec in MS */
-static struct timer_list verify_tsc_freq_timer;
-
-/* XXX - Probably should add locking */
-static void verify_tsc_freq(unsigned long unused)
-{
-        static u64 last_tsc;
-        static unsigned long last_jiffies;
-
-        u64 now_tsc, interval_tsc;
-        unsigned long now_jiffies, interval_jiffies;
-
-
-        if (check_tsc_unstable())
-                return;
-
-        rdtscll(now_tsc);
-        now_jiffies = jiffies;
-
-        if (!last_jiffies) {
-                goto out;
-        }
-
-        interval_jiffies = now_jiffies - last_jiffies;
-        interval_tsc = now_tsc - last_tsc;
-        interval_tsc *= HZ;
-        do_div(interval_tsc, cpu_khz*1000);
-
-        if (interval_tsc < (interval_jiffies * 3 / 4)) {
-                printk("TSC appears to be running slowly. "
-                        "Marking it as unstable\n");
-                mark_tsc_unstable();
-                return;
-        }
-
-out:
-        last_tsc = now_tsc;
-        last_jiffies = now_jiffies;
-        /* set us up to go off on the next interval: */
-        mod_timer(&verify_tsc_freq_timer,
-                jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL));
-}
-
 /*
  * Make an educated guess if the TSC is trustworthy and synchronized
  * over all CPUs.
@@ -424,12 +381,6 @@ static int __init init_tsc_clocksource(void)
                         clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
                 }
 
-                init_timer(&verify_tsc_freq_timer);
-                verify_tsc_freq_timer.function = verify_tsc_freq;
-                verify_tsc_freq_timer.expires =
-                        jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL);
-                add_timer(&verify_tsc_freq_timer);
-
                 return clocksource_register(&clocksource_tsc);
         }
 
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index a585a29fe7c4..830a250ecf94 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -12,11 +12,13 @@
 #include <linux/timex.h>
 #include <linux/time.h>
 #include <linux/list.h>
+#include <linux/timer.h>
 #include <asm/div64.h>
 #include <asm/io.h>
 
 /* clocksource cycle base type */
 typedef u64 cycle_t;
+struct clocksource;
 
 /**
  * struct clocksource - hardware abstraction for a free running counter
@@ -62,13 +64,22 @@ struct clocksource {
         cycle_t cycle_last, cycle_interval;
         u64 xtime_nsec, xtime_interval;
         s64 error;
+
+#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
+        /* Watchdog related data, used by the framework */
+        struct list_head wd_list;
+        cycle_t wd_last;
+#endif
 };
 
 /*
  * Clock source flags bits::
  */
-#define CLOCK_SOURCE_IS_CONTINUOUS      0x01
-#define CLOCK_SOURCE_MUST_VERIFY        0x02
+#define CLOCK_SOURCE_IS_CONTINUOUS              0x01
+#define CLOCK_SOURCE_MUST_VERIFY                0x02
+
+#define CLOCK_SOURCE_WATCHDOG                   0x10
+#define CLOCK_SOURCE_VALID_FOR_HRES             0x20
 
 /* simplify initialization of mask field */
 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 2f6a3d6e43bc..3cb8ac978270 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -63,9 +63,116 @@ static int __init clocksource_done_booting(void)
         finished_booting = 1;
         return 0;
 }
-
 late_initcall(clocksource_done_booting);
 
+#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
+static LIST_HEAD(watchdog_list);
+static struct clocksource *watchdog;
+static struct timer_list watchdog_timer;
+static DEFINE_SPINLOCK(watchdog_lock);
+static cycle_t watchdog_last;
+/*
+ * Interval: 0.5sec Treshold: 0.0625s
+ */
+#define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_TRESHOLD (NSEC_PER_SEC >> 4)
+
+static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
+{
+        if (delta > -WATCHDOG_TRESHOLD && delta < WATCHDOG_TRESHOLD)
+                return;
+
+        printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
+               cs->name, delta);
+        cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
+        clocksource_change_rating(cs, 0);
+        cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
+        list_del(&cs->wd_list);
+}
+
+static void clocksource_watchdog(unsigned long data)
+{
+        struct clocksource *cs, *tmp;
+        cycle_t csnow, wdnow;
+        int64_t wd_nsec, cs_nsec;
+
+        spin_lock(&watchdog_lock);
+
+        wdnow = watchdog->read();
+        wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
+        watchdog_last = wdnow;
+
+        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
+                csnow = cs->read();
+                /* Initialized ? */
+                if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
+                        if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
+                            (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
+                                cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+                        }
+                        cs->flags |= CLOCK_SOURCE_WATCHDOG;
+                        cs->wd_last = csnow;
+                } else {
+                        cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
+                        cs->wd_last = csnow;
+                        /* Check the delta. Might remove from the list ! */
+                        clocksource_ratewd(cs, cs_nsec - wd_nsec);
+                }
+        }
+
+        if (!list_empty(&watchdog_list)) {
+                __mod_timer(&watchdog_timer,
+                            watchdog_timer.expires + WATCHDOG_INTERVAL);
+        }
+        spin_unlock(&watchdog_lock);
+}
+static void clocksource_check_watchdog(struct clocksource *cs)
+{
+        struct clocksource *cse;
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+                int started = !list_empty(&watchdog_list);
+
+                list_add(&cs->wd_list, &watchdog_list);
+                if (!started && watchdog) {
+                        watchdog_last = watchdog->read();
+                        watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
+                        add_timer(&watchdog_timer);
+                }
+        } else if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) {
+                        cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+
+                if (!watchdog || cs->rating > watchdog->rating) {
+                        if (watchdog)
+                                del_timer(&watchdog_timer);
+                        watchdog = cs;
+                        init_timer(&watchdog_timer);
+                        watchdog_timer.function = clocksource_watchdog;
+
+                        /* Reset watchdog cycles */
+                        list_for_each_entry(cse, &watchdog_list, wd_list)
+                                cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
+                        /* Start if list is not empty */
+                        if (!list_empty(&watchdog_list)) {
+                                watchdog_last = watchdog->read();
+                                watchdog_timer.expires =
+                                        jiffies + WATCHDOG_INTERVAL;
+                                add_timer(&watchdog_timer);
+                        }
+                }
+        }
+        spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+#else
+static void clocksource_check_watchdog(struct clocksource *cs)
+{
+        if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
+                cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+}
+#endif
+
 /**
  * clocksource_get_next - Returns the selected clocksource
  *
@@ -94,13 +201,21 @@ struct clocksource *clocksource_get_next(void)
  */
 static struct clocksource *select_clocksource(void)
 {
+        struct clocksource *next;
+
         if (list_empty(&clocksource_list))
                 return NULL;
 
         if (clocksource_override)
-                return clocksource_override;
+                next = clocksource_override;
+        else
+                next = list_entry(clocksource_list.next, struct clocksource,
+                                  list);
 
-        return list_entry(clocksource_list.next, struct clocksource, list);
+        if (next == curr_clocksource)
+                return NULL;
+
+        return next;
 }
 
 /*
@@ -138,13 +253,15 @@ static int clocksource_enqueue(struct clocksource *c)
 int clocksource_register(struct clocksource *c)
 {
         unsigned long flags;
-        int ret = 0;
+        int ret;
 
         spin_lock_irqsave(&clocksource_lock, flags);
         ret = clocksource_enqueue(c);
         if (!ret)
                 next_clocksource = select_clocksource();
         spin_unlock_irqrestore(&clocksource_lock, flags);
+        if (!ret)
+                clocksource_check_watchdog(c);
         return ret;
 }
 EXPORT_SYMBOL(clocksource_register);
@@ -159,6 +276,7 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
 
         spin_lock_irqsave(&clocksource_lock, flags);
         list_del(&cs->list);
+        cs->rating = rating;
         clocksource_enqueue(cs);
         next_clocksource = select_clocksource();
         spin_unlock_irqrestore(&clocksource_lock, flags);
diff --git a/kernel/timer.c b/kernel/timer.c
index 4b088fcadb3f..b68a21a82e17 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -832,30 +832,33 @@ EXPORT_SYMBOL(do_settimeofday);
  *
  * Accumulates current time interval and initializes new clocksource
  */
-static int change_clocksource(void)
+static void change_clocksource(void)
 {
         struct clocksource *new;
         cycle_t now;
         u64 nsec;
+
         new = clocksource_get_next();
-        if (clock != new) {
-                now = clocksource_read(new);
-                nsec =  __get_nsec_offset();
-                timespec_add_ns(&xtime, nsec);
-
-                clock = new;
-                clock->cycle_last = now;
-                printk(KERN_INFO "Time: %s clocksource has been installed.\n",
-                       clock->name);
-                return 1;
-        }
-        return 0;
+
+        if (clock == new)
+                return;
+
+        now = clocksource_read(new);
+        nsec =  __get_nsec_offset();
+        timespec_add_ns(&xtime, nsec);
+
+        clock = new;
+        clock->cycle_last = now;
+
+        clock->error = 0;
+        clock->xtime_nsec = 0;
+        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
+
+        printk(KERN_INFO "Time: %s clocksource has been installed.\n",
+               clock->name);
 }
 #else
-static inline int change_clocksource(void)
-{
-        return 0;
-}
+static inline void change_clocksource(void) { }
 #endif
 
 /**
@@ -869,7 +872,7 @@ int timekeeping_is_continuous(void)
         do {
                 seq = read_seqbegin(&xtime_lock);
 
-                ret = clock->flags & CLOCK_SOURCE_IS_CONTINUOUS;
+                ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
 
         } while (read_seqretry(&xtime_lock, seq));
 
@@ -1124,11 +1127,7 @@ static void update_wall_time(void)
         clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 
         /* check to see if there is a new clocksource to use */
-        if (change_clocksource()) {
-                clock->error = 0;
-                clock->xtime_nsec = 0;
-                clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
-        }
+        change_clocksource();
 }
 
 /*