From c131a198c497db436b558ac5e9a140cdcb91b304 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 26 Apr 2018 11:34:23 +0100 Subject: [PATCH] locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node When a locker reaches the head of the queue and takes the lock, a concurrent locker may enqueue and force the lock holder to spin whilst its node->next field is initialised. Rather than open-code a READ_ONCE/cpu_relax() loop, this can be implemented using smp_cond_load_relaxed() instead. Signed-off-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Cc: Linus Torvalds Cc: Thomas Gleixner Cc: boqun.feng@gmail.com Cc: linux-arm-kernel@lists.infradead.org Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1524738868-31318-10-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar --- kernel/locking/qspinlock.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 56af1fa9874d..d6c3b029bd93 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -483,10 +483,8 @@ locked: /* * contended path; wait for next if not observed yet, release. */ - if (!next) { - while (!(next = READ_ONCE(node->next))) - cpu_relax(); - } + if (!next) + next = smp_cond_load_relaxed(&node->next, (VAL)); arch_mcs_spin_unlock_contended(&next->locked); pv_kick_node(lock, next); -- 2.11.0