From: Davidlohr Bueso Date: Mon, 20 Sep 2021 05:20:30 +0000 (-0700) Subject: locking/rwbase: Optimize rwbase_read_trylock X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=c78416d122243c92992a1d1063f17ddd0bc80e6c;p=linux.git 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 Signed-off-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@stgolabs.net --- diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c index 15c81100f0e26..6fd3162e4098f 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);