On 2016年05月27日 00:57, Peter Zijlstra wrote:

On Thu, May 26, 2016 at 06:47:29PM +0200, Peter Zijlstra wrote:

quoted

On Wed, May 25, 2016 at 04:18:08PM +0800, Pan Xinhui wrote:

quoted

cmpxchg_release is light-wight than cmpxchg, we can gain a better
performace then. On some arch like ppc, barrier impact the performace
too much.

Suggested-by:  Boqun Feng <redacted>
Signed-off-by: Pan Xinhui <redacted>
---
  kernel/locking/qspinlock_paravirt.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index a5b1248..2bbffe4 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h

@@ -614,7 +614,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
  	 * unhash. Otherwise it would be possible to have multiple @lock
  	 * entries, which would be BAD.
  	 */
-	locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+	locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
  	if (likely(locked == _Q_LOCKED_VAL))
  		return;

This patch fails to explain _why_ it can be relaxed.

And seeing how this cmpxchg() can actually unlock the lock, I don't see
how this can possibly be correct. Maybe cmpxchg_release(), but relaxed
seems very wrong.

Clearly I need to stop working for the day, I cannea read. You're doing
release, not relaxed.

Never mind.  thanks for review :)

Still Changelog needs improvement.

Will do that.

thanks
xinhui