The following commit has been merged into the locking/core branch of tip:
Commit-ID: c78416d122243c92992a1d1063f17ddd0bc80e6c
Gitweb: https://git.kernel.org/tip/c78416d122243c92992a1d1063f17ddd0bc80e6c
Author: Davidlohr Bueso <dave@xxxxxxxxxxxx>
AuthorDate: Sun, 19 Sep 2021 22:20:30 -07:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 07 Oct 2021 13:51:07 +02:00
locking/rwbase: Optimize rwbase_read_trylock
Instead of a full barrier around the Rmw insn, micro-optimize
for weakly ordered archs such that we only provide the required
ACQUIRE semantics when taking the read lock.
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@xxxxxxxxxxxx
---
kernel/locking/rwbase_rt.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 15c8110..6fd3162 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -59,8 +59,7 @@ static __always_inline int rwbase_read_trylock(struct rwbase_rt *rwb)
* set.
*/
for (r = atomic_read(&rwb->readers); r < 0;) {
- /* Fully-ordered if cmpxchg() succeeds, provides ACQUIRE */
- if (likely(atomic_try_cmpxchg(&rwb->readers, &r, r + 1)))
+ if (likely(atomic_try_cmpxchg_acquire(&rwb->readers, &r, r + 1)))
return 1;
}
return 0;
@@ -187,7 +186,7 @@ static inline void __rwbase_write_unlock(struct rwbase_rt *rwb, int bias,
/*
* _release() is needed in case that reader is in fast path, pairing
- * with atomic_try_cmpxchg() in rwbase_read_trylock(), provides RELEASE
+ * with atomic_try_cmpxchg_acquire() in rwbase_read_trylock().
*/
(void)atomic_add_return_release(READER_BIAS - bias, &rwb->readers);
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
|