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Subject[patch 18/46] clocksource: Add verification (watchdog) helper
From: Thomas Gleixner <tglx@linutronix.de>

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>

---
arch/i386/Kconfig | 4 +
arch/i386/kernel/tsc.c | 49 -----------------
include/linux/clocksource.h | 15 ++++-
kernel/time/clocksource.c | 125 ++++++++++++++++++++++++++++++++++++++++++--
kernel/timer.c | 46 ++++++++--------
5 files changed, 161 insertions(+), 78 deletions(-)

Index: linux-2.6.20-rc4-mm1-bo/arch/i386/kernel/tsc.c
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/arch/i386/kernel/tsc.c
+++ linux-2.6.20-rc4-mm1-bo/arch/i386/kernel/tsc.c
@@ -344,49 +344,6 @@ static struct dmi_system_id __initdata b
{}
};

-#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(v
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);
}

Index: linux-2.6.20-rc4-mm1-bo/include/linux/clocksource.h
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/include/linux/clocksource.h
+++ linux-2.6.20-rc4-mm1-bo/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)
Index: linux-2.6.20-rc4-mm1-bo/kernel/time/clocksource.c
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/kernel/time/clocksource.c
+++ linux-2.6.20-rc4-mm1-bo/kernel/time/clocksource.c
@@ -62,9 +62,115 @@ static int __init clocksource_done_booti
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
*
@@ -93,13 +199,21 @@ struct clocksource *clocksource_get_next
*/
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;
}

/*
@@ -137,13 +251,15 @@ static int clocksource_enqueue(struct cl
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);
@@ -158,6 +274,7 @@ void clocksource_change_rating(struct cl

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);
Index: linux-2.6.20-rc4-mm1-bo/kernel/timer.c
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/kernel/timer.c
+++ linux-2.6.20-rc4-mm1-bo/kernel/timer.c
@@ -832,30 +832,34 @@ 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);
+
+ hrtimer_clock_notify();
+ 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 +873,7 @@ 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));

@@ -1122,11 +1126,7 @@ 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();
}

/*
Index: linux-2.6.20-rc4-mm1-bo/arch/i386/Kconfig
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/arch/i386/Kconfig
+++ linux-2.6.20-rc4-mm1-bo/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
--

-
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