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[Xen-devel] [PATCH 2/4] time: add a notifier chain for when the system time is stepped



From: David Vrabel <david.vrabel@xxxxxxxxxx>

The high resolution timer code gets notified of step changes to the
system time with clock_was_set() or clock_was_set_delayed() calls.  If
other parts of the kernel require similar notification there is no
clear place to hook into.

Add a clock_was_set atomic notifier chain
(clock_was_set_notifier_list) and call this in place of
clock_was_set().  If the timekeeping locks are held, the calls are
deferred to a new tasklet.

The hrtimer code adds a notifier block to this chain and uses it to
call (the now internal) clock_was_set().  Since the timekeeping code
does not call the chain from the timer irq clock_was_set_delayed() and
associated code can be removed.

For the delayed case, clock_was_set() used to be called at the
beginning of the hrtimer softirq and now it is called from a tasklet.
The tasklet softirq will be called before the hrtimer one so this
should give the same behaviour.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 include/linux/hrtimer.h   |    7 -------
 include/linux/time.h      |    7 +++++++
 kernel/hrtimer.c          |   34 +++++++++++++---------------------
 kernel/time/timekeeping.c |   39 ++++++++++++++++++++++++++++++---------
 4 files changed, 50 insertions(+), 37 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 13df0fa..45e30f6 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -166,7 +166,6 @@ enum  hrtimer_base_type {
  * @lock:              lock protecting the base and associated clock bases
  *                     and timers
  * @active_bases:      Bitfield to mark bases with active timers
- * @clock_was_set:     Indicates that clock was set from irq context.
  * @expires_next:      absolute time of the next event which was scheduled
  *                     via clock_set_next_event()
  * @hres_active:       State of high resolution mode
@@ -180,7 +179,6 @@ enum  hrtimer_base_type {
 struct hrtimer_cpu_base {
        raw_spinlock_t                  lock;
        unsigned int                    active_bases;
-       unsigned int                    clock_was_set;
 #ifdef CONFIG_HIGH_RES_TIMERS
        ktime_t                         expires_next;
        int                             hres_active;
@@ -289,8 +287,6 @@ extern void hrtimer_peek_ahead_timers(void);
 # define MONOTONIC_RES_NSEC    HIGH_RES_NSEC
 # define KTIME_MONOTONIC_RES   KTIME_HIGH_RES
 
-extern void clock_was_set_delayed(void);
-
 #else
 
 # define MONOTONIC_RES_NSEC    LOW_RES_NSEC
@@ -312,11 +308,8 @@ static inline int hrtimer_is_hres_active(struct hrtimer 
*timer)
        return 0;
 }
 
-static inline void clock_was_set_delayed(void) { }
-
 #endif
 
-extern void clock_was_set(void);
 #ifdef CONFIG_TIMERFD
 extern void timerfd_clock_was_set(void);
 #else
diff --git a/include/linux/time.h b/include/linux/time.h
index d5d229b..a0c08a7 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -184,6 +184,13 @@ extern void timekeeping_clocktai(struct timespec *ts);
 struct tms;
 extern void do_sys_times(struct tms *);
 
+struct notifier_block;
+
+/*
+ * Notifier chain called when system time is stepped.
+ */
+extern int register_clock_was_set_notifier(struct notifier_block *nb);
+
 /*
  * Similar to the struct tm in userspace <time.h>, but it needs to be here so
  * that the kernel source is self contained.
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 34384b4..a853f9b 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -721,19 +721,6 @@ static int hrtimer_switch_to_hres(void)
        return 1;
 }
 
-/*
- * Called from timekeeping code to reprogramm the hrtimer interrupt
- * device. If called from the timer interrupt context we defer it to
- * softirq context.
- */
-void clock_was_set_delayed(void)
-{
-       struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
-
-       cpu_base->clock_was_set = 1;
-       __raise_softirq_irqoff(HRTIMER_SOFTIRQ);
-}
-
 #else
 
 static inline int hrtimer_hres_active(void) { return 0; }
@@ -762,7 +749,7 @@ static inline void retrigger_next_event(void *arg) { }
  * resolution timer interrupts. On UP we just disable interrupts and
  * call the high resolution interrupt code.
  */
-void clock_was_set(void)
+static void clock_was_set(void)
 {
 #ifdef CONFIG_HIGH_RES_TIMERS
        /* Retrigger the CPU local events everywhere */
@@ -1441,13 +1428,6 @@ void hrtimer_peek_ahead_timers(void)
 
 static void run_hrtimer_softirq(struct softirq_action *h)
 {
-       struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
-
-       if (cpu_base->clock_was_set) {
-               cpu_base->clock_was_set = 0;
-               clock_was_set();
-       }
-
        hrtimer_peek_ahead_timers();
 }
 
@@ -1785,11 +1765,23 @@ static struct notifier_block __cpuinitdata hrtimers_nb 
= {
        .notifier_call = hrtimer_cpu_notify,
 };
 
+static int hrtimer_clock_was_set_notify(struct notifier_block *self,
+                                       unsigned long action, void *data)
+{
+       clock_was_set();
+       return NOTIFY_OK;
+}
+
+static struct notifier_block hrtimers_clock_was_set_nb = {
+       .notifier_call = hrtimer_clock_was_set_notify,
+};
+
 void __init hrtimers_init(void)
 {
        hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,
                          (void *)(long)smp_processor_id());
        register_cpu_notifier(&hrtimers_nb);
+       register_clock_was_set_notifier(&hrtimers_clock_was_set_nb);
 #ifdef CONFIG_HIGH_RES_TIMERS
        open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq);
 #endif
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index baeeb5c..96c5c8e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -198,6 +198,30 @@ static inline s64 timekeeping_get_ns_raw(struct timekeeper 
*tk)
        return nsec + get_arch_timeoffset();
 }
 
+static ATOMIC_NOTIFIER_HEAD(clock_was_set_notifier_list);
+
+int register_clock_was_set_notifier(struct notifier_block *nb)
+{
+       return atomic_notifier_chain_register(&clock_was_set_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(register_clock_was_set_notifier);
+
+static void timekeeping_clock_was_set(void)
+{
+       atomic_notifier_call_chain(&clock_was_set_notifier_list, 0, NULL);
+}
+
+static void timekeeping_clock_was_set_task(unsigned long d)
+{
+       timekeeping_clock_was_set();
+}
+DECLARE_TASKLET(clock_was_set_tasklet, timekeeping_clock_was_set_task, 0);
+
+static void timekeeping_clock_was_set_delayed(void)
+{
+       tasklet_schedule(&clock_was_set_tasklet);
+}
+
 static RAW_NOTIFIER_HEAD(pvclock_gtod_chain);
 
 static void update_pvclock_gtod(struct timekeeper *tk)
@@ -513,8 +537,7 @@ int do_settimeofday(const struct timespec *tv)
        write_seqcount_end(&timekeeper_seq);
        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
-       /* signal hrtimers about time change */
-       clock_was_set();
+       timekeeping_clock_was_set();
 
        return 0;
 }
@@ -557,8 +580,7 @@ error: /* even if we error out, we forwarded the time, so 
call update */
        write_seqcount_end(&timekeeper_seq);
        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
-       /* signal hrtimers about time change */
-       clock_was_set();
+       timekeeping_clock_was_set();
 
        return ret;
 }
@@ -607,7 +629,7 @@ void timekeeping_set_tai_offset(s32 tai_offset)
        __timekeeping_set_tai_offset(tk, tai_offset);
        write_seqcount_end(&timekeeper_seq);
        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
-       clock_was_set();
+       timekeeping_clock_was_set();
 }
 
 /**
@@ -877,8 +899,7 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
        write_seqcount_end(&timekeeper_seq);
        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
-       /* signal hrtimers about time change */
-       clock_was_set();
+       timekeeping_clock_was_set();
 }
 
 /**
@@ -1260,7 +1281,7 @@ static inline void accumulate_nsecs_to_secs(struct 
timekeeper *tk)
 
                        __timekeeping_set_tai_offset(tk, tk->tai_offset - leap);
 
-                       clock_was_set_delayed();
+                       timekeeping_clock_was_set_delayed();
                }
        }
 }
@@ -1677,7 +1698,7 @@ int do_adjtimex(struct timex *txc)
 
        if (tai != orig_tai) {
                __timekeeping_set_tai_offset(tk, tai);
-               clock_was_set_delayed();
+               timekeeping_clock_was_set_delayed();
        }
        write_seqcount_end(&timekeeper_seq);
        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
-- 
1.7.2.5


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