osq_lock() starts by setting node->next to NULL and node->locked to 0. Careful analysis shows that node->next is always NULL on entry. node->locked is set non-zero by another cpu to force a wakeup. This can only happen after the 'prev->next = node' assignment, so locked can be set to zero just before that (along with the assignment to node->prev). Only initialise node->cpu once, after that use its value instead of smp_processor_id() - which is probably a real function call. Should reduce cache-line bouncing a little. Signed-off-by: David Laight <david.laight@xxxxxxxxxx> --- Re-send without the 'RE:' on the subject line. kernel/locking/osq_lock.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index d414eef4bec6..55f5db896c02 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -51,7 +51,7 @@ osq_wait_next(struct optimistic_spin_queue *lock, struct optimistic_spin_node *prev) { struct optimistic_spin_node *next = NULL; - int curr = encode_cpu(smp_processor_id()); + int curr = node->cpu; int old; /* @@ -98,12 +98,10 @@ bool osq_lock(struct optimistic_spin_queue *lock) { struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); struct optimistic_spin_node *prev, *next; - int curr = encode_cpu(smp_processor_id()); int old; - node->locked = 0; - node->next = NULL; - node->cpu = curr; + if (unlikely(node->cpu == OSQ_UNLOCKED_VAL)) + node->cpu = encode_cpu(smp_processor_id()); /* * We need both ACQUIRE (pairs with corresponding RELEASE in @@ -111,12 +109,13 @@ bool osq_lock(struct optimistic_spin_queue *lock) * the node fields we just initialised) semantics when updating * the lock tail. */ - old = atomic_xchg(&lock->tail, curr); + old = atomic_xchg(&lock->tail, node->cpu); if (old == OSQ_UNLOCKED_VAL) return true; prev = decode_cpu(old); node->prev = prev; + node->locked = 0; /* * osq_lock() unqueue @@ -214,7 +213,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) void osq_unlock(struct optimistic_spin_queue *lock) { struct optimistic_spin_node *node, *next; - int curr = encode_cpu(smp_processor_id()); + int curr = raw_cpu_read(osq_node.cpu); /* * Fast path for the uncontended case. -- 2.17.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)