cpu/hotplug: Make wait for dead cpu completion based

Kill the busy spinning on the control side and just wait for the hotplugged
cpu to tell that it reached the dead state.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Rik van Riel <riel@redhat.com>
Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20160226182341.776157858@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 83f35767016d59c3ff56d91482c0c03380ae5a78..91a48d1b4ca01346e89efcd9737487f34f0c1c7a 100644 (file)
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -276,14 +276,15 @@ void arch_cpu_idle_enter(void);
 void arch_cpu_idle_exit(void);
 void arch_cpu_idle_dead(void);
 
-DECLARE_PER_CPU(bool, cpu_dead_idle);
-
 int cpu_report_state(int cpu);
 int cpu_check_up_prepare(int cpu);
 void cpu_set_state_online(int cpu);
 #ifdef CONFIG_HOTPLUG_CPU
 bool cpu_wait_death(unsigned int cpu, int seconds);
 bool cpu_report_death(void);
+void cpuhp_report_idle_dead(void);
+#else
+static inline void cpuhp_report_idle_dead(void) { }
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 
 #endif /* _LINUX_CPU_H_ */

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index ad5d7fcb013021811c57a87bc8a7b6e798142a34..5d68e15e46b779d4cb0ff4613fd77d28403c72b5 100644 (file)
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -6,6 +6,7 @@ enum cpuhp_state {
        CPUHP_CREATE_THREADS,
        CPUHP_NOTIFY_PREPARE,
        CPUHP_BRINGUP_CPU,
+       CPUHP_AP_IDLE_DEAD,
        CPUHP_AP_OFFLINE,
        CPUHP_AP_NOTIFY_STARTING,
        CPUHP_AP_ONLINE,

diff --git a/kernel/cpu.c b/kernel/cpu.c
index f1f880fac83217dfcb6cc7a3b0446ee50f36d89a..0e8c07f2566e8de4bb3814dccc6b1413f4b0b95a 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -688,6 +688,7 @@ static int take_cpu_down(void *_param)
 
 static int takedown_cpu(unsigned int cpu)
 {
+       struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int err;
 
        /*
@@ -733,10 +734,8 @@ static int takedown_cpu(unsigned int cpu)
         *
         * Wait for the stop thread to go away.
         */
-       while (!per_cpu(cpu_dead_idle, cpu))
-               cpu_relax();
-       smp_mb(); /* Read from cpu_dead_idle before __cpu_die(). */
-       per_cpu(cpu_dead_idle, cpu) = false;
+       wait_for_completion(&st->done);
+       BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
 
        /* Interrupts are moved away from the dying cpu, reenable alloc/free */
        irq_unlock_sparse();
@@ -756,6 +755,15 @@ static int notify_dead(unsigned int cpu)
        return 0;
 }
 
+void cpuhp_report_idle_dead(void)
+{
+       struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
+
+       BUG_ON(st->state != CPUHP_AP_OFFLINE);
+       st->state = CPUHP_AP_IDLE_DEAD;
+       complete(&st->done);
+}
+
 #else
 #define notify_down_prepare    NULL
 #define takedown_cpu           NULL

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index a4b9813afc964b8cb4872fa5ebd2ababfe13b988..8abbe89e91143c417dd986b81be76be379eb8001 100644 (file)
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -194,8 +194,6 @@ exit_idle:
        rcu_idle_exit();
 }
 
-DEFINE_PER_CPU(bool, cpu_dead_idle);
-
 /*
  * Generic idle loop implementation
  *
@@ -224,8 +222,7 @@ static void cpu_idle_loop(void)
                        if (cpu_is_offline(smp_processor_id())) {
                                rcu_cpu_notify(NULL, CPU_DYING_IDLE,
                                               (void *)(long)smp_processor_id());
-                               smp_mb(); /* all activity before dead. */
-                               this_cpu_write(cpu_dead_idle, true);
+                               cpuhp_report_idle_dead();
                                arch_cpu_idle_dead();
                        }