sched: Simplify wake_up_*idle*()

Simplify and make wake_up_if_idle() more robust, also don't iterate
the whole machine with preempt_disable() in it's caller:
wake_up_all_idle_cpus().

This prepares for another wake_up_if_idle() user that needs a full
do_idle() cycle.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Tested-by: Vasily Gorbik <gor@linux.ibm.com> # on s390
Link: https://lkml.kernel.org/r/20210929152428.769328779@infradead.org

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 74db3c3..3b55ef9 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3695,15 +3695,11 @@ void wake_up_if_idle(int cpu)
        if (!is_idle_task(rcu_dereference(rq->curr)))
                goto out;
 
-       if (set_nr_if_polling(rq->idle)) {
-               trace_sched_wake_idle_without_ipi(cpu);
-       } else {
-               rq_lock_irqsave(rq, &rf);
-               if (is_idle_task(rq->curr))
-                       smp_send_reschedule(cpu);
-               /* Else CPU is not idle, do nothing here: */
-               rq_unlock_irqrestore(rq, &rf);
-       }
+       rq_lock_irqsave(rq, &rf);
+       if (is_idle_task(rq->curr))
+               resched_curr(rq);
+       /* Else CPU is not idle, do nothing here: */
+       rq_unlock_irqrestore(rq, &rf);
 
 out:
        rcu_read_unlock();

diff --git a/kernel/smp.c b/kernel/smp.c
index f43ede0..ad0b68a 100644 (file)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -1170,14 +1170,14 @@ void wake_up_all_idle_cpus(void)
 {
        int cpu;
 
-       preempt_disable();
+       cpus_read_lock();
        for_each_online_cpu(cpu) {
-               if (cpu == smp_processor_id())
+               if (cpu == raw_smp_processor_id())
                        continue;
 
                wake_up_if_idle(cpu);
        }
-       preempt_enable();
+       cpus_read_unlock();
 }
 EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);