[patch 31/40] sched: Convert fair nohz balancer to hotplug state machine

[Thomas Gleixner]

Straight forward conversion which leaves the question whether this
couldn't be combined with already existing infrastructure in the
scheduler instead of having an extra state.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
 include/linux/cpuhotplug.h |    6 ++++++
 kernel/cpu.c               |    4 ++++
 kernel/sched/fair.c        |   16 ++--------------
 3 files changed, 12 insertions(+), 14 deletions(-)

Index: linux-2.6/include/linux/cpuhotplug.h
===================================================================
--- linux-2.6.orig/include/linux/cpuhotplug.h
+++ linux-2.6/include/linux/cpuhotplug.h
@@ -29,6 +29,7 @@ enum cpuhp_states {
        CPUHP_AP_NOTIFY_DYING,
        CPUHP_AP_X86_TBOOT_DYING,
        CPUHP_AP_S390_VTIME_DYING,
+       CPUHP_AP_SCHED_NOHZ_DYING,
        CPUHP_AP_SCHED_MIGRATE_DYING,
        CPUHP_AP_MAX,
        CPUHP_TEARDOWN_CPU,
@@ -126,6 +127,11 @@ int sched_migration_dead_cpu(unsigned in
 #define sched_migration_dying_cpu      NULL
 #define sched_migration_dead_cpu       NULL
 #endif
+#if defined(CONFIG_NO_HZ)
+int nohz_balance_exit_idle(unsigned int cpu);
+#else
+#define nohz_balance_exit_idle         NULL
+#endif
 
  /* Performance counter hotplug functions */
 #ifdef CONFIG_PERF_EVENTS
Index: linux-2.6/kernel/cpu.c
===================================================================
--- linux-2.6.orig/kernel/cpu.c
+++ linux-2.6/kernel/cpu.c
@@ -813,6 +813,10 @@ static struct cpuhp_step cpuhp_ap_states
                .startup = NULL,
                .teardown = notify_dying,
        },
+       [CPUHP_AP_SCHED_NOHZ_DYING] = {
+               .startup = NULL,
+               .teardown = nohz_balance_exit_idle,
+       },
        [CPUHP_AP_SCHED_MIGRATE_DYING] = {
                .startup = NULL,
                .teardown = sched_migration_dying_cpu,
Index: linux-2.6/kernel/sched/fair.c
===================================================================
--- linux-2.6.orig/kernel/sched/fair.c
+++ linux-2.6/kernel/sched/fair.c
@@ -5390,13 +5390,14 @@ static void nohz_balancer_kick(int cpu)
        return;
 }
 
-static inline void nohz_balance_exit_idle(int cpu)
+int nohz_balance_exit_idle(unsigned int cpu)
 {
        if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
                cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
                atomic_dec(&nohz.nr_cpus);
                clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
        }
+       return 0;
 }
 
 static inline void set_cpu_sd_state_busy(void)
@@ -5448,18 +5449,6 @@ void nohz_balance_enter_idle(int cpu)
        atomic_inc(&nohz.nr_cpus);
        set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
 }
-
-static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb,
-                                       unsigned long action, void *hcpu)
-{
-       switch (action & ~CPU_TASKS_FROZEN) {
-       case CPU_DYING:
-               nohz_balance_exit_idle(smp_processor_id());
-               return NOTIFY_OK;
-       default:
-               return NOTIFY_DONE;
-       }
-}
 #endif
 
 static DEFINE_SPINLOCK(balancing);
@@ -6167,7 +6156,6 @@ __init void init_sched_fair_class(void)
 #ifdef CONFIG_NO_HZ
        nohz.next_balance = jiffies;
        zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
-       cpu_notifier(sched_ilb_notifier, 0);
 #endif
 #endif /* SMP */
 


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