Commit-ID: c131a198c497db436b558ac5e9a140cdcb91b304 Gitweb: https://git.kernel.org/tip/c131a198c497db436b558ac5e9a140cdcb91b304 Author: Will Deacon <[email protected]> AuthorDate: Thu, 26 Apr 2018 11:34:23 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 27 Apr 2018 09:48:50 +0200
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 <[email protected]> Acked-by: Peter Zijlstra (Intel) <[email protected]> Acked-by: Waiman Long <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- 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);
