[RFC][PATCH 4/7] sched: Simplify wake_up_*idle*()

Peter Zijlstra
2021-09-22T11:11:32Z

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>
---
kernel/sched/core.c | 14 +++++---------
kernel/smp.c | 6 +++---
2 files changed, 8 insertions(+), 12 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3691,15 +3691,11 @@ 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();
--- 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);