linux-kernel - [tip: core/rcu] kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock

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Date:   Sun, 11 Apr 2021 13:43:40 -0000
From:   "tip-bot2 for Paul E. McKenney" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/rcu] kvfree_rcu: Make krc_this_cpu_unlock() use
 raw_spin_unlock_irqrestore()

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

Commit-ID:     7ffc9ec8eac196cbd85669a4d7920cd80f186a51
Gitweb:        https://git.kernel.org/tip/7ffc9ec8eac196cbd85669a4d7920cd80f186a51
Author:        Paul E. McKenney <paulmck@...nel.org>
AuthorDate:    Wed, 20 Jan 2021 13:38:08 -08:00
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Mon, 08 Mar 2021 14:18:07 -08:00

kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock_irqrestore()

The krc_this_cpu_unlock() function does a raw_spin_unlock() immediately
followed by a local_irq_restore().  This commit saves a line of code by
merging them into a raw_spin_unlock_irqrestore().  This transformation
also reduces scheduling latency because raw_spin_unlock_irqrestore()
responds immediately to a reschedule request.  In contrast,
local_irq_restore() does a scheduling-oblivious enabling of interrupts.

Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 08b5044..7ee83f3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3229,8 +3229,7 @@ krc_this_cpu_lock(unsigned long *flags)
 static inline void
 krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
 {
-	raw_spin_unlock(&krcp->lock);
-	local_irq_restore(flags);
+	raw_spin_unlock_irqrestore(&krcp->lock, flags);
 }
 
 static inline struct kvfree_rcu_bulk_data *