From:   Lai Jiangshan <jiangshanlai@gmail.com>
To:     linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Subject: [PATCH 4/4] workqueue: Convert the type of pool->nr_running to int
Date:   Thu, 23 Dec 2021 20:31:40 +0800
Message-Id: <20211223123140.3789-5-jiangshanlai@gmail.com>
In-Reply-To: <20211223123140.3789-1-jiangshanlai@gmail.com>
References: <20211223123140.3789-1-jiangshanlai@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Lai Jiangshan <laijs@linux.alibaba.com>

It is only modified in associated CPU, so it doesn't need to be atomic.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 kernel/workqueue.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 69cbe9e62bf1..dd3b3aa68954 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -154,8 +154,13 @@ struct worker_pool {
 
 	unsigned long		watchdog_ts;	/* L: watchdog timestamp */
 
-	/* The current concurrency level. */
-	atomic_t		nr_running;
+	/*
+	 * The current concurrency level.
+	 * increase: process context in associated CPU (preemption disabled).
+	 * decrease and reset: process context in associated CPU & pool->lock.
+	 * read: pool->lock. Ensured to be seen when decreased or reset to zero.
+	 */
+	int			nr_running;
 
 	struct list_head	worklist;	/* L: list of pending works */
 
@@ -777,7 +782,7 @@ static bool work_is_canceling(struct work_struct *work)
 
 static bool __need_more_worker(struct worker_pool *pool)
 {
-	return !atomic_read(&pool->nr_running);
+	return !pool->nr_running;
 }
 
 /*
@@ -802,8 +807,7 @@ static bool may_start_working(struct worker_pool *pool)
 /* Do I need to keep working?  Called from currently running workers. */
 static bool keep_working(struct worker_pool *pool)
 {
-	return !list_empty(&pool->worklist) &&
-		atomic_read(&pool->nr_running) <= 1;
+	return !list_empty(&pool->worklist) && (pool->nr_running <= 1);
 }
 
 /* Do we need a new worker?  Called from manager. */
@@ -873,7 +877,7 @@ void wq_worker_running(struct task_struct *task)
 	 */
 	preempt_disable();
 	if (!(worker->flags & WORKER_NOT_RUNNING))
-		atomic_inc(&worker->pool->nr_running);
+		worker->pool->nr_running++;
 	preempt_enable();
 	worker->sleeping = 0;
 }
@@ -917,8 +921,8 @@ void wq_worker_sleeping(struct task_struct *task)
 		return;
 	}
 
-	if (atomic_dec_and_test(&pool->nr_running) &&
-	    !list_empty(&pool->worklist))
+	pool->nr_running--;
+	if (need_more_worker(pool))
 		wake_up_worker(pool);
 	raw_spin_unlock_irq(&pool->lock);
 }
@@ -973,7 +977,7 @@ static inline void worker_set_flags(struct worker *worker, unsigned int flags)
 	/* If transitioning into NOT_RUNNING, adjust nr_running. */
 	if ((flags & WORKER_NOT_RUNNING) &&
 	    !(worker->flags & WORKER_NOT_RUNNING)) {
-		atomic_dec(&pool->nr_running);
+		pool->nr_running--;
 	}
 
 	worker->flags |= flags;
@@ -1005,7 +1009,7 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
 	 */
 	if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
 		if (!(worker->flags & WORKER_NOT_RUNNING))
-			atomic_inc(&pool->nr_running);
+			pool->nr_running++;
 }
 
 /**
@@ -1806,8 +1810,7 @@ static void worker_enter_idle(struct worker *worker)
 		mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
 
 	/* Sanity check nr_running. */
-	WARN_ON_ONCE(pool->nr_workers == pool->nr_idle &&
-		     atomic_read(&pool->nr_running));
+	WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
 }
 
 /**
@@ -4985,7 +4988,7 @@ static void unbind_workers(int cpu)
 		 * an unbound (in terms of concurrency management) pool which
 		 * are served by workers tied to the pool.
 		 */
-		atomic_set(&pool->nr_running, 0);
+		pool->nr_running = 0;
 
 		/*
 		 * With concurrency management just turned off, a busy
-- 
2.19.1.6.gb485710b