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>

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index f3cc653..1feb9c7 100644 (file)
--- 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);