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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Cc: Tejun Heo <tj@kernel.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.8 007/715] workqueue: Make wq_adjust_max_active() round-robin pwqs while activating
Date: Sun, 24 Mar 2024 18:23:06 -0400
Message-ID: <20240324223455.1342824-8-sashal@kernel.org>
In-Reply-To: <20240324223455.1342824-1-sashal@kernel.org>
References: <20240324223455.1342824-1-sashal@kernel.org>
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From: Tejun Heo <tj@kernel.org>

[ Upstream commit c5404d4e6df6faba1007544b5f4e62c7c14416dd ]

wq_adjust_max_active() needs to activate work items after max_active is
increased. Previously, it did that by visiting each pwq once activating all
that could be activated. While this makes sense with per-pwq nr_active,
nr_active will be shared across multiple pwqs for unbound wqs. Then, we'd
want to round-robin through pwqs to be fairer.

In preparation, this patch makes wq_adjust_max_active() round-robin pwqs
while activating. While the activation ordering changes, this shouldn't
cause user-noticeable behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Stable-dep-of: 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/workqueue.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 80733046ee012..1659cd4a36c62 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4703,7 +4703,7 @@ static int init_rescuer(struct workqueue_struct *wq)
  */
 static void wq_adjust_max_active(struct workqueue_struct *wq)
 {
-	struct pool_workqueue *pwq;
+	bool activated;
 
 	lockdep_assert_held(&wq->mutex);
 
@@ -4723,19 +4723,26 @@ static void wq_adjust_max_active(struct workqueue_struct *wq)
 	 */
 	WRITE_ONCE(wq->max_active, wq->saved_max_active);
 
-	for_each_pwq(pwq, wq) {
-		unsigned long flags;
-
-		/* this function can be called during early boot w/ irq disabled */
-		raw_spin_lock_irqsave(&pwq->pool->lock, flags);
-
-		while (pwq_activate_first_inactive(pwq))
-			;
+	/*
+	 * Round-robin through pwq's activating the first inactive work item
+	 * until max_active is filled.
+	 */
+	do {
+		struct pool_workqueue *pwq;
 
-		kick_pool(pwq->pool);
+		activated = false;
+		for_each_pwq(pwq, wq) {
+			unsigned long flags;
 
-		raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
-	}
+			/* can be called during early boot w/ irq disabled */
+			raw_spin_lock_irqsave(&pwq->pool->lock, flags);
+			if (pwq_activate_first_inactive(pwq)) {
+				activated = true;
+				kick_pool(pwq->pool);
+			}
+			raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
+		}
+	} while (activated);
 }
 
 __printf(1, 4)
-- 
2.43.0