linux-kernel - [tip: sched/core] sched: Simplify wake_up

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Date:   Sat, 09 Oct 2021 10:07:39 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vasily Gorbik <gor@...ux.ibm.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Simplify wake_up_*idle*()

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     8850cb663b5cda04d33f9cfbc38889d73d3c8e24
Gitweb:        https://git.kernel.org/tip/8850cb663b5cda04d33f9cfbc38889d73d3c8e24
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 21 Sep 2021 22:16:02 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 07 Oct 2021 13:51:15 +02:00

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>
Acked-by: Vasily Gorbik <gor@...ux.ibm.com>
Tested-by: Vasily Gorbik <gor@...ux.ibm.com> # on s390
Link: https://lkml.kernel.org/r/20210929152428.769328779@infradead.org
---
 kernel/sched/core.c | 14 +++++---------
 kernel/smp.c        |  6 +++---
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 74db3c3..3b55ef9 100644
--- 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
--- 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);