linux-kernel - [PATCH v2 10/12] locking/qspinlock: paravirt use simple trylock in case idx overflows

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Message-Id: <20220713070704.308394-11-npiggin@gmail.com>
Date:   Wed, 13 Jul 2022 17:07:02 +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 @ vger . kernel . org" <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 10/12] locking/qspinlock: paravirt use simple trylock in case idx overflows

The mcs node overflow fallback locking case does not have to use
pv_hybrid_queued_unfair_trylock as the trylock, which reduces the
differences between pv and !pv cases.

This was likely an artifact of function renaming making it use the pv
trylock, which is not a bug but it is unexpected.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
 kernel/locking/qspinlock.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index df6d8af8f2a9..2ebb946a6b80 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -800,13 +800,8 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
 	 */
 	if (unlikely(idx >= MAX_NODES)) {
 		lockevent_inc(lock_no_node);
-		if (paravirt) {
-			while (!pv_hybrid_queued_unfair_trylock(lock))
-				cpu_relax();
-		} else {
-			while (!queued_spin_trylock(lock))
-				cpu_relax();
-		}
+		while (!queued_spin_trylock(lock))
+			cpu_relax();
 		goto release;
 	}
 
-- 
2.35.1