Messages in this thread Patch in this message | | | From | Michel Lespinasse <> | Subject | [PATCH v2 09/13] rwsem: skip initial trylock in rwsem_down_write_failed | Date | Fri, 15 Mar 2013 03:54:25 -0700 |
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We can skip the initial trylock in rwsem_down_write_failed() if there are known active lockers already, thus saving one likely-to-fail cmpxchg.
Signed-off-by: Michel Lespinasse <walken@google.com>
--- lib/rwsem.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/lib/rwsem.c b/lib/rwsem.c index edf3d9ca670e..0d50e46d5b0c 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -216,14 +216,15 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) /* wait until we successfully acquire the lock */ set_task_state(tsk, TASK_UNINTERRUPTIBLE); while (true) { - - /* Try acquiring the write lock. */ - count = RWSEM_ACTIVE_WRITE_BIAS; - if (!list_is_singular(&sem->wait_list)) - count += RWSEM_WAITING_BIAS; - if (cmpxchg(&sem->count, RWSEM_WAITING_BIAS, count) == + if (!(count & RWSEM_ACTIVE_MASK)) { + /* Try acquiring the write lock. */ + count = RWSEM_ACTIVE_WRITE_BIAS; + if (!list_is_singular(&sem->wait_list)) + count += RWSEM_WAITING_BIAS; + if (cmpxchg(&sem->count, RWSEM_WAITING_BIAS, count) == RWSEM_WAITING_BIAS) - break; + break; + } raw_spin_unlock_irq(&sem->wait_lock); @@ -231,7 +232,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) do { schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); - } while (sem->count & RWSEM_ACTIVE_MASK); + } while ((count = sem->count) & RWSEM_ACTIVE_MASK); raw_spin_lock_irq(&sem->wait_lock); } -- 1.8.1.3
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