From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756098Ab1IGGaq (ORCPT ); Wed, 7 Sep 2011 02:30:46 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:48768 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755643Ab1IGGUs (ORCPT ); Wed, 7 Sep 2011 02:20:48 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 34/55] rcu: Move __rcu_read_unlock()'s barrier() within if-statement Date: Tue, 6 Sep 2011 11:00:28 -0700 Message-Id: <1315332049-2604-34-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110906180015.GA2560@linux.vnet.ibm.com> References: <20110906180015.GA2560@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paul E. McKenney We only need to constrain the compiler if we are actually exiting the top-level RCU read-side critical section. This commit therefore moves the first barrier() cal in __rcu_read_unlock() to inside the "if" statement, thus avoiding needless register flushes for inner rcu_read_unlock() calls. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 14 ++------------ kernel/rcutree_plugin.h | 2 +- 2 files changed, 3 insertions(+), 13 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 9873040..e86bc28 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -134,16 +134,6 @@ extern void call_rcu_sched(struct rcu_head *head, extern void synchronize_sched(void); -static inline void __rcu_read_lock_bh(void) -{ - local_bh_disable(); -} - -static inline void __rcu_read_unlock_bh(void) -{ - local_bh_enable(); -} - #ifdef CONFIG_PREEMPT_RCU extern void __rcu_read_lock(void); @@ -686,7 +676,7 @@ static inline void rcu_read_unlock(void) */ static inline void rcu_read_lock_bh(void) { - __rcu_read_lock_bh(); + local_bh_disable(); __acquire(RCU_BH); rcu_read_acquire_bh(); } @@ -700,7 +690,7 @@ static inline void rcu_read_unlock_bh(void) { rcu_read_release_bh(); __release(RCU_BH); - __rcu_read_unlock_bh(); + local_bh_enable(); } /** diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 4bac5a2..ed70f6b 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -415,10 +415,10 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; - barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ if (t->rcu_read_lock_nesting != 1) --t->rcu_read_lock_nesting; else { + barrier(); /* critical section before exit code. */ t->rcu_read_lock_nesting = INT_MIN; barrier(); /* assign before ->rcu_read_unlock_special load */ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) -- 1.7.3.2