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From: Yanfei Xu <yanfei.xu@windriver.com>
To: peterz@infradead.org, mingo@redhat.com, will@kernel.org,
	longman@redhat.com, boqun.feng@gmail.com
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH V2 3/3] locking/rwsem: fix comments about reader optimistic lock stealing conditions
Date: Wed, 13 Oct 2021 21:41:54 +0800	[thread overview]
Message-ID: <20211013134154.1085649-4-yanfei.xu@windriver.com> (raw)
In-Reply-To: <20211013134154.1085649-1-yanfei.xu@windriver.com>

After the commit 617f3ef95177 ("locking/rwsem: Remove reader
optimistic spinning"), reader doesn't support optimistic spinning
anymore, there is no need meet the condition which OSQ is empty.

BTW, add an unlikely() for the max reader wakeup check in the loop.

Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
---
 kernel/locking/rwsem.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 06925b43c3e7..2bd914187399 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -56,7 +56,6 @@
  *
  * A fast path reader optimistic lock stealing is supported when the rwsem
  * is previously owned by a writer and the following conditions are met:
- *  - OSQ is empty
  *  - rwsem is not currently writer owned
  *  - the handoff isn't set.
  */
@@ -485,7 +484,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
 		/*
 		 * Limit # of readers that can be woken up per wakeup call.
 		 */
-		if (woken >= MAX_READERS_WAKEUP)
+		if (unlikely(woken >= MAX_READERS_WAKEUP))
 			break;
 	}
 
-- 
2.27.0


  parent reply	other threads:[~2021-10-13 13:42 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-13 13:41 [PATCH V2 0/3] misc patches for mutex and rwsem Yanfei Xu
2021-10-13 13:41 ` [PATCH V2 1/3] locking: remove rcu_read_lock/unlock as we already disabled preemption Yanfei Xu
2021-10-19 15:35   ` [tip: locking/core] locking: Remove rcu_read_{,un}lock() for preempt_{dis,en}able() tip-bot2 for Yanfei Xu
2021-10-13 13:41 ` [PATCH v2 2/3] locking/rwsem: disable preemption for spinning region Yanfei Xu
2021-10-15 10:13   ` Peter Zijlstra
2021-10-15 10:20     ` Peter Zijlstra
2021-10-15 12:33       ` Xu, Yanfei
2021-10-19 15:35   ` [tip: locking/core] locking/rwsem: Disable " tip-bot2 for Yanfei Xu
2021-10-13 13:41 ` Yanfei Xu [this message]
2021-10-19 15:35   ` [tip: locking/core] locking/rwsem: Fix comments about reader optimistic lock stealing conditions tip-bot2 for Yanfei Xu
2021-10-13 21:08 ` [PATCH V2 0/3] misc patches for mutex and rwsem Waiman Long

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