This patch applies on top of linux-next. Commit 9b0fc9c09f1b added an extra check in rwsem_down_write_failed() for if there are known active lockers in order to avoid doing the cmpxchg() that would likely be unnecessary.
However, a subsequent change was made such that we check for sem->count == RWSEM_WAITING_BIAS right before trying that cmpxchg(). Thus, the first check added in commit 9b0fc9c09f1b now adds extra overhead. This patch deletes it. Note: we are now changing the rwsem_try_write_lock() as the relevant code was recently moved into that function. Signed-off-by: Jason Low <[email protected]> --- kernel/locking/rwsem-xadd.c | 16 +++++++--------- 1 files changed, 7 insertions(+), 9 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 1f99664..6d01f2f 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -247,15 +247,13 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem) { - if (!(count & RWSEM_ACTIVE_MASK)) { - /* try acquiring the write lock */ - if (sem->count == RWSEM_WAITING_BIAS && - cmpxchg(&sem->count, RWSEM_WAITING_BIAS, - RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) { - if (!list_is_singular(&sem->wait_list)) - rwsem_atomic_update(RWSEM_WAITING_BIAS, sem); - return true; - } + /* try acquiring the write lock */ + if (sem->count == RWSEM_WAITING_BIAS && + cmpxchg(&sem->count, RWSEM_WAITING_BIAS, + RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) { + if (!list_is_singular(&sem->wait_list)) + rwsem_atomic_update(RWSEM_WAITING_BIAS, sem); + return true; } return false; } -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
