linux-kernel - [PATCH] sched: Make preempt_enable_no_resched() behave like preempt_enable() on PREEMPT

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Message-ID: <Yh5mSGCbvqDdeCa3@linutronix.de>
Date:   Tue, 1 Mar 2022 19:30:32 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] sched: Make preempt_enable_no_resched() behave like
 preempt_enable() on PREEMPT_RT

From: Thomas Gleixner <tglx@...utronix.de>

Use the distinction that has been made earlier between
preempt_enable_no_resched() and sched_preempt_enable_no_resched().
sched_preempt_enable_no_resched() is used within the scheduler where an
immediate schedule() follows. preempt_enable_no_resched() is used
outside of the scheduler and an immediate schedule() invocation may not
follow for other reasons.

The lack of an immediate schedule() invocation matters on PREEMPT_RT
where it will introduce latencies while the scheduler expects a context
switch.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/linux/preempt.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index b4381f255a5ca..582e43856a532 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -210,7 +210,11 @@ do { \
 	preempt_count_dec(); \
 } while (0)
 
-#define preempt_enable_no_resched() sched_preempt_enable_no_resched()
+#ifdef CONFIG_PREEMPT_RT
+# define preempt_enable_no_resched() preempt_enable()
+#else
+# define preempt_enable_no_resched() sched_preempt_enable_no_resched()
+#endif
 
 #define preemptible()	(preempt_count() == 0 && !irqs_disabled())
 
-- 
2.35.1