timer: Don't initialize 'tvec_base' on hotplug

There is no need to call init_timers_cpu() on every CPU hotplug event,
there is not much we need to reset.

 - Timer-lists are already empty at the end of migrate_timers().
 - timer_jiffies will be refreshed while adding a new timer, after the
   CPU is online again.
 - active_timers and all_timers can be reset from migrate_timers().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/54a1c30ea7b805af55beb220cadf5a07a21b0a4d.1427814611.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 43 insertions, 55 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index f3cc653f876c..1feb9c7035c0 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1543,43 +1543,6 @@ signed long __sched schedule_timeout_uninterruptible(signed long timeout)
 }
 EXPORT_SYMBOL(schedule_timeout_uninterruptible);
 
-static int init_timers_cpu(int cpu)
-{
-        struct tvec_base *base = per_cpu(tvec_bases, cpu);
-        static char tvec_base_done[NR_CPUS];
-        int j;
-
-        if (!tvec_base_done[cpu]) {
-                static char boot_cpu_skipped;
-
-                if (!boot_cpu_skipped) {
-                        boot_cpu_skipped = 1; /* skip the boot cpu */
-                } else {
-                        base = per_cpu_ptr(&__tvec_bases, cpu);
-                        per_cpu(tvec_bases, cpu) = base;
-                }
-
-                spin_lock_init(&base->lock);
-                tvec_base_done[cpu] = 1;
-                base->cpu = cpu;
-        }
-
-        for (j = 0; j < TVN_SIZE; j++) {
-                INIT_LIST_HEAD(base->tv5.vec + j);
-                INIT_LIST_HEAD(base->tv4.vec + j);
-                INIT_LIST_HEAD(base->tv3.vec + j);
-                INIT_LIST_HEAD(base->tv2.vec + j);
-        }
-        for (j = 0; j < TVR_SIZE; j++)
-                INIT_LIST_HEAD(base->tv1.vec + j);
-
-        base->timer_jiffies = jiffies;
-        base->next_timer = base->timer_jiffies;
-        base->active_timers = 0;
-        base->all_timers = 0;
-        return 0;
-}
-
 #ifdef CONFIG_HOTPLUG_CPU
 static void migrate_timer_list(struct tvec_base *new_base, struct list_head *head)
 {
@@ -1621,6 +1584,9 @@ static void migrate_timers(int cpu)
                 migrate_timer_list(new_base, old_base->tv5.vec + i);
         }
 
+        old_base->active_timers = 0;
+        old_base->all_timers = 0;
+
         spin_unlock(&old_base->lock);
         spin_unlock_irq(&new_base->lock);
         put_cpu_var(tvec_bases);
@@ -1630,25 +1596,16 @@ static void migrate_timers(int cpu)
 static int timer_cpu_notify(struct notifier_block *self,
                                 unsigned long action, void *hcpu)
 {
-        long cpu = (long)hcpu;
-        int err;
-
-        switch(action) {
-        case CPU_UP_PREPARE:
-        case CPU_UP_PREPARE_FROZEN:
-                err = init_timers_cpu(cpu);
-                if (err < 0)
-                        return notifier_from_errno(err);
-                break;
 #ifdef CONFIG_HOTPLUG_CPU
+        switch (action) {
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
-                migrate_timers(cpu);
+                migrate_timers((long)hcpu);
                 break;
-#endif
         default:
                 break;
         }
+#endif
         return NOTIFY_OK;
 }
 
@@ -1656,18 +1613,49 @@ static struct notifier_block timers_nb = {
         .notifier_call  = timer_cpu_notify,
 };
 
+static void __init init_timer_cpu(struct tvec_base *base, int cpu)
+{
+        int j;
 
-void __init init_timers(void)
+        base->cpu = cpu;
+        per_cpu(tvec_bases, cpu) = base;
+        spin_lock_init(&base->lock);
+
+        for (j = 0; j < TVN_SIZE; j++) {
+                INIT_LIST_HEAD(base->tv5.vec + j);
+                INIT_LIST_HEAD(base->tv4.vec + j);
+                INIT_LIST_HEAD(base->tv3.vec + j);
+                INIT_LIST_HEAD(base->tv2.vec + j);
+        }
+        for (j = 0; j < TVR_SIZE; j++)
+                INIT_LIST_HEAD(base->tv1.vec + j);
+
+        base->timer_jiffies = jiffies;
+        base->next_timer = base->timer_jiffies;
+}
+
+static void __init init_timer_cpus(void)
 {
-        int err;
+        struct tvec_base *base;
+        int local_cpu = smp_processor_id();
+        int cpu;
+
+        for_each_possible_cpu(cpu) {
+                if (cpu == local_cpu)
+                        base = &boot_tvec_bases;
+                else
+                        base = per_cpu_ptr(&__tvec_bases, cpu);
+
+                init_timer_cpu(base, cpu);
+        }
+}
 
+void __init init_timers(void)
+{
         /* ensure there are enough low bits for flags in timer->base pointer */
         BUILD_BUG_ON(__alignof__(struct tvec_base) & TIMER_FLAG_MASK);
 
-        err = timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE,
-                               (void *)(long)smp_processor_id());
-        BUG_ON(err != NOTIFY_OK);
-
+        init_timer_cpus();
         init_timer_stats();
         register_cpu_notifier(&timers_nb);
         open_softirq(TIMER_SOFTIRQ, run_timer_softirq);