From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: [ofa-general] [PATCH 06 of 11] rwsem contended Date: Fri, 02 May 2008 17:05:09 +0200 Message-ID: <74b873f3ea07012e2fc8.1209740709@duo.random> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Nick Piggin , Chris Wright , Rusty Russell , Peter Zijlstra , Marcelo Tosatti , kvm-devel@lists.sourceforge.net, Kanoj Sarcar , Roland Dreier , Jack Steiner , linux-kernel@vger.kernel.org, Avi Kivity , Anthony Liguori , "Paul E. McKenney" , linux-mm@kvack.org, Robin Holt , general@lists.openfabrics.org, Hugh Dickins , akpm@linux-foundation.org, Eric Dumazet , Christoph Lameter To: Andrew Morton Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: general-bounces@lists.openfabrics.org Errors-To: general-bounces@lists.openfabrics.org List-Id: kvm.vger.kernel.org # HG changeset patch # User Andrea Arcangeli # Date 1209740186 -7200 # Node ID 74b873f3ea07012e2fc864f203edf1179865feb1 # Parent a8ac53b928dfcea0ccb326fb7d71f908f0df85f4 rwsem contended Add a function to rw_semaphores to check if there are any processes waiting for the semaphore. Add rwsem_needbreak to sched.h that works in the same way as spinlock_needbreak(). Signed-off-by: Christoph Lameter Signed-off-by: Andrea Arcangeli diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -57,6 +57,8 @@ extern void up_write(struct rw_semaphore */ extern void downgrade_write(struct rw_semaphore *sem); +extern int rwsem_is_contended(struct rw_semaphore *sem); + #ifdef CONFIG_DEBUG_LOCK_ALLOC /* * nested locking. NOTE: rwsems are not allowed to recurse diff --git a/include/linux/sched.h b/include/linux/sched.h --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2030,6 +2030,15 @@ static inline int spin_needbreak(spinloc #endif } +static inline int rwsem_needbreak(struct rw_semaphore *sem) +{ +#ifdef CONFIG_PREEMPT + return rwsem_is_contended(sem); +#else + return 0; +#endif +} + /* * Reevaluate whether the task has signals pending delivery. * Wake the task if so. diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c --- a/lib/rwsem-spinlock.c +++ b/lib/rwsem-spinlock.c @@ -305,6 +305,18 @@ void __downgrade_write(struct rw_semapho spin_unlock_irqrestore(&sem->wait_lock, flags); } +int rwsem_is_contended(struct rw_semaphore *sem) +{ + /* + * Racy check for an empty list. False positives or negatives + * would be okay. False positive may cause a useless dropping of + * locks. False negatives may cause locks to be held a bit + * longer until the next check. + */ + return !list_empty(&sem->wait_list); +} + +EXPORT_SYMBOL(rwsem_is_contended); EXPORT_SYMBOL(__init_rwsem); EXPORT_SYMBOL(__down_read); EXPORT_SYMBOL(__down_read_trylock); diff --git a/lib/rwsem.c b/lib/rwsem.c --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -251,6 +251,18 @@ asmregparm struct rw_semaphore *rwsem_do return sem; } +int rwsem_is_contended(struct rw_semaphore *sem) +{ + /* + * Racy check for an empty list. False positives or negatives + * would be okay. False positive may cause a useless dropping of + * locks. False negatives may cause locks to be held a bit + * longer until the next check. + */ + return !list_empty(&sem->wait_list); +} + +EXPORT_SYMBOL(rwsem_is_contended); EXPORT_SYMBOL(rwsem_down_read_failed); EXPORT_SYMBOL(rwsem_down_write_failed); EXPORT_SYMBOL(rwsem_wake);