linux-kernel - [RFC][PATCH 4/7] sched: Simplify wake_up

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Message-ID: <20210922110836.125579666@infradead.org>
Date:   Wed, 22 Sep 2021 13:05:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     gor@...ux.ibm.com, jpoimboe@...hat.com, jikos@...nel.org,
        mbenes@...e.cz, pmladek@...e.com, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        joe.lawrence@...hat.com, fweisbec@...il.com, tglx@...utronix.de,
        hca@...ux.ibm.com, svens@...ux.ibm.com, sumanthk@...ux.ibm.com,
        live-patching@...r.kernel.org, paulmck@...nel.org
Subject: [RFC][PATCH 4/7] 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@...radead.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);