this_cpu_ptr() is rather more expensive than raw_cpu_read() since
the latter can use an 'offset from register' (%gs for x86-84).
Add a 'self' field to 'struct optimistic_spin_node' that can be
read with raw_cpu_read(), initialise on first call.
Signed-off-by: David Laight <david.laight@xxxxxxxxxx>
---
kernel/locking/osq_lock.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 9bb3a077ba92..b60b0add0161 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -13,7 +13,7 @@
*/
struct optimistic_spin_node {
- struct optimistic_spin_node *next, *prev;
+ struct optimistic_spin_node *self, *next, *prev;
int locked; /* 1 if lock acquired */
int cpu; /* encoded CPU # + 1 value */
};
@@ -93,12 +93,16 @@ osq_wait_next(struct optimistic_spin_queue *lock,
bool osq_lock(struct optimistic_spin_queue *lock)
{
- struct optimistic_spin_node *node = this_cpu_ptr(&osq_node);
+ struct optimistic_spin_node *node = raw_cpu_read(osq_node.self);
struct optimistic_spin_node *prev, *next;
int old;
- if (unlikely(node->cpu == OSQ_UNLOCKED_VAL))
- node->cpu = encode_cpu(smp_processor_id());
+ if (unlikely(!node)) {
+ int cpu = encode_cpu(smp_processor_id());
+ node = decode_cpu(cpu);
+ node->self = node;
+ node->cpu = cpu;
+ }
/*
* We need both ACQUIRE (pairs with corresponding RELEASE in
@@ -222,7 +226,7 @@ void osq_unlock(struct optimistic_spin_queue *lock)
/*
* Second most likely case.
*/
- node = this_cpu_ptr(&osq_node);
+ node = raw_cpu_read(osq_node.self);
next = xchg(&node->next, NULL);
if (next) {
WRITE_ONCE(next->locked, 1);
--
2.17.1
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
