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authorWaiman Long <longman@redhat.com>2019-04-04 13:43:13 -0400
committerIngo Molnar <mingo@kernel.org>2019-04-10 10:56:01 +0200
commita338ecb07a338c9a8b0ca0010e862ebe598b1551 (patch)
tree8dae984357ba838cd16a28c8dbc099edf0ebd473 /kernel/locking
parent12a30a7fc142a123c61da9623bd824d95d36c12e (diff)
locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued()
The atomic_long_cmpxchg_acquire() in rwsem_try_read_lock_unqueued() is replaced by atomic_long_try_cmpxchg_acquire() to simpify the code and generate slightly better assembly code. There is no functional change. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Link: http://lkml.kernel.org/r/20190404174320.22416-5-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rwsem-xadd.c15
1 files changed, 5 insertions, 10 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index c213869e1aa7..f6198e1a58f6 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -259,21 +259,16 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
- long old, count = atomic_long_read(&sem->count);
+ long count = atomic_long_read(&sem->count);
- while (true) {
- if (!(count == 0 || count == RWSEM_WAITING_BIAS))
- return false;
-
- old = atomic_long_cmpxchg_acquire(&sem->count, count,
- count + RWSEM_ACTIVE_WRITE_BIAS);
- if (old == count) {
+ while (!count || count == RWSEM_WAITING_BIAS) {
+ if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
+ count + RWSEM_ACTIVE_WRITE_BIAS)) {
rwsem_set_owner(sem);
return true;
}
-
- count = old;
}
+ return false;
}
static inline bool owner_on_cpu(struct task_struct *owner)