Commit-ID: 33ecd2083a9560fbc1ef1b1279ef3ecb4c012a4f Gitweb: http://git.kernel.org/tip/33ecd2083a9560fbc1ef1b1279ef3ecb4c012a4f Author: Jason Low <[email protected]> AuthorDate: Mon, 14 Jul 2014 10:27:51 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Wed, 16 Jul 2014 13:28:06 +0200
locking/spinlocks/mcs: Micro-optimize osq_unlock() In the unlock function of the cancellable MCS spinlock, the first thing we do is to retrive the current CPU's osq node. However, due to the changes made in the previous patch, in the common case where the lock is not contended, we wouldn't need to access the current CPU's osq node anymore. This patch optimizes this by only retriving this CPU's osq node after we attempt the initial cmpxchg to unlock the osq and found that its contended. Signed-off-by: Jason Low <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Cc: Scott Norton <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Dave Chinner <[email protected]> Cc: Waiman Long <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Andrew Morton <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Tim Chen <[email protected]> Cc: Konrad Rzeszutek Wilk <[email protected]> Cc: Aswin Chandramouleeswaran <[email protected]> Cc: Linus Torvalds <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/locking/mcs_spinlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/mcs_spinlock.c b/kernel/locking/mcs_spinlock.c index 32fc16c..be9ee15 100644 --- a/kernel/locking/mcs_spinlock.c +++ b/kernel/locking/mcs_spinlock.c @@ -182,8 +182,7 @@ unqueue: void osq_unlock(struct optimistic_spin_queue *lock) { - struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); - struct optimistic_spin_node *next; + struct optimistic_spin_node *node, *next; int curr = encode_cpu(smp_processor_id()); /* @@ -195,6 +194,7 @@ void osq_unlock(struct optimistic_spin_queue *lock) /* * Second most likely case. */ + node = this_cpu_ptr(&osq_node); next = xchg(&node->next, NULL); if (next) { ACCESS_ONCE(next->locked) = 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/
