Messages in this thread Patch in this message | | | From | Will Deacon <> | Subject | [PATCH v2 08/13] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node | Date | Wed, 11 Apr 2018 19:01:15 +0100 |
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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.
Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Will Deacon <will.deacon@arm.com> --- 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 648a16a2cd23..c781ddbe59a6 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -523,10 +523,8 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* * 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); -- 2.1.4
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