linux-kernel - [PATCH 12/13] locking/qspinlock: separate pv_wait

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Date:   Tue,  5 Jul 2022 00:38:19 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 12/13] locking/qspinlock: separate pv_wait_node from the non-paravirt path

pv_wait_node waits until node->locked is non-zero, no need for the
pv case to wait again by also executing the !pv code path.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
 kernel/locking/qspinlock.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 9db168753124..19e2f286be0a 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -862,10 +862,11 @@ static inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, bool parav
 		/* Link @node into the waitqueue. */
 		WRITE_ONCE(prev->next, node);
 
+		/* Wait for mcs node lock to be released */
 		if (paravirt)
 			pv_wait_node(node, prev);
-		/* Wait for mcs node lock to be released */
-		smp_cond_load_acquire(&node->locked, VAL);
+		else
+			smp_cond_load_acquire(&node->locked, VAL);
 
 		/*
 		 * While waiting for the MCS lock, the next pointer may have
-- 
2.35.1