* [RFC PATCH] rwsem: Avoid double checking before trylock for rwsem_try_write_lock()
@ 2014-06-04 19:01 Jason Low
0 siblings, 0 replies; only message in thread
From: Jason Low @ 2014-06-04 19:01 UTC (permalink / raw)
To: mingo, peterz, tglx, akpm
Cc: linux-kernel, paulmck, tim.c.chen, peter, riel, hpa, walken,
davidlohr, Waiman.Long, aswin, scott.norton, chegu_vinod,
Jason Low
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 <jason.low2@hp.com>
---
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
^ permalink raw reply related [flat|nested] only message in thread
only message in thread, other threads:[~2014-06-04 19:01 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-06-04 19:01 [RFC PATCH] rwsem: Avoid double checking before trylock for rwsem_try_write_lock() Jason Low
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.