sched: Start stopper early

Ensure the stopper thread is active 'early', because the load balancer
pretty much assumes that its available. And when 'online && active' the
load-balancer is fully available.

Not only the numa balancing stop_two_cpus() caller relies on it, but
also the self migration stuff does, and at CPU_ONLINE time the cpu
really is 'free' to run anything.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: heiko.carstens@de.ibm.com
Link: http://lkml.kernel.org/r/20151009160054.GA10176@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6467521e1e15a0637685387a100823487b953c50..c85df2775b735895d0637c416c712f507828dd9d 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -475,7 +475,6 @@ static int smpboot_thread_call(struct notifier_block *nfb,
 
        case CPU_DOWN_FAILED:
        case CPU_ONLINE:
-               stop_machine_unpark(cpu);
                smpboot_unpark_threads(cpu);
                break;
 

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f45a7c70f2648c92353450e99b9d296a697cb0cb..7ee8caea119538bad3a5833e122d306c5199729b 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5545,21 +5545,27 @@ static void set_cpu_rq_start_time(void)
 static int sched_cpu_active(struct notifier_block *nfb,
                                      unsigned long action, void *hcpu)
 {
+       int cpu = (long)hcpu;
+
        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_STARTING:
                set_cpu_rq_start_time();
                return NOTIFY_OK;
+
        case CPU_ONLINE:
                /*
                 * At this point a starting CPU has marked itself as online via
                 * set_cpu_online(). But it might not yet have marked itself
                 * as active, which is essential from here on.
-                *
-                * Thus, fall-through and help the starting CPU along.
                 */
+               set_cpu_active(cpu, true);
+               stop_machine_unpark(cpu);
+               return NOTIFY_OK;
+
        case CPU_DOWN_FAILED:
-               set_cpu_active((long)hcpu, true);
+               set_cpu_active(cpu, true);
                return NOTIFY_OK;
+
        default:
                return NOTIFY_DONE;
        }