linux-kernel - [PATCH v9 6/7] sched: Split out __schedule() deactivate task logic into a helper

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Message-ID: <20240315044007.2778856-7-jstultz@google.com>
Date: Thu, 14 Mar 2024 21:39:51 -0700
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: John Stultz <jstultz@...gle.com>, Joel Fernandes <joelaf@...gle.com>, 
	Qais Yousef <qyousef@...gle.com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Valentin Schneider <vschneid@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Zimuzo Ezeozue <zezeozue@...gle.com>, 
	Youssef Esmat <youssefesmat@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, 
	Boqun Feng <boqun.feng@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>, 
	Metin Kaya <Metin.Kaya@....com>, Xuewen Yan <xuewen.yan94@...il.com>, 
	K Prateek Nayak <kprateek.nayak@....com>, Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com
Subject: [PATCH v9 6/7] sched: Split out __schedule() deactivate task logic
 into a helper

As we're going to re-use the deactivation logic,
split it into a helper.

Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Qais Yousef <qyousef@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
Cc: Youssef Esmat <youssefesmat@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Metin Kaya <Metin.Kaya@....com>
Cc: Xuewen Yan <xuewen.yan94@...il.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kernel-team@...roid.com
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v6:
* Define function as static to avoid "no previous prototype"
  warnings as Reported-by: kernel test robot <lkp@...el.com>
v7:
* Rename state task_state to be more clear, as suggested by
  Metin Kaya
---
 kernel/sched/core.c | 72 +++++++++++++++++++++++++++------------------
 1 file changed, 43 insertions(+), 29 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ad4748327651..b537e5f501ea 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6563,6 +6563,48 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 # define SM_MASK_PREEMPT	SM_PREEMPT
 #endif
 
+/*
+ * Helper function for __schedule()
+ *
+ * If a task does not have signals pending, deactivate it and return true
+ * Otherwise marks the task's __state as RUNNING and returns false
+ */
+static bool try_to_deactivate_task(struct rq *rq, struct task_struct *p,
+				   unsigned long task_state)
+{
+	if (signal_pending_state(task_state, p)) {
+		WRITE_ONCE(p->__state, TASK_RUNNING);
+	} else {
+		p->sched_contributes_to_load =
+			(task_state & TASK_UNINTERRUPTIBLE) &&
+			!(task_state & TASK_NOLOAD) &&
+			!(task_state & TASK_FROZEN);
+
+		if (p->sched_contributes_to_load)
+			rq->nr_uninterruptible++;
+
+		/*
+		 * __schedule()			ttwu()
+		 *   prev_state = prev->state;    if (p->on_rq && ...)
+		 *   if (prev_state)		    goto out;
+		 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
+		 *				  p->state = TASK_WAKING
+		 *
+		 * Where __schedule() and ttwu() have matching control dependencies.
+		 *
+		 * After this, schedule() must not care about p->state any more.
+		 */
+		deactivate_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
+
+		if (p->in_iowait) {
+			atomic_inc(&rq->nr_iowait);
+			delayacct_blkio_start();
+		}
+		return true;
+	}
+	return false;
+}
+
 /*
  * __schedule() is the main scheduler function.
  *
@@ -6654,35 +6696,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 	 */
 	prev_state = READ_ONCE(prev->__state);
 	if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
-		if (signal_pending_state(prev_state, prev)) {
-			WRITE_ONCE(prev->__state, TASK_RUNNING);
-		} else {
-			prev->sched_contributes_to_load =
-				(prev_state & TASK_UNINTERRUPTIBLE) &&
-				!(prev_state & TASK_NOLOAD) &&
-				!(prev_state & TASK_FROZEN);
-
-			if (prev->sched_contributes_to_load)
-				rq->nr_uninterruptible++;
-
-			/*
-			 * __schedule()			ttwu()
-			 *   prev_state = prev->state;    if (p->on_rq && ...)
-			 *   if (prev_state)		    goto out;
-			 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
-			 *				  p->state = TASK_WAKING
-			 *
-			 * Where __schedule() and ttwu() have matching control dependencies.
-			 *
-			 * After this, schedule() must not care about p->state any more.
-			 */
-			deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
-
-			if (prev->in_iowait) {
-				atomic_inc(&rq->nr_iowait);
-				delayacct_blkio_start();
-			}
-		}
+		try_to_deactivate_task(rq, prev, prev_state);
 		switch_count = &prev->nvcsw;
 	}
 
-- 
2.44.0.291.gc1ea87d7ee-goog