Messages in this thread Patch in this message | | | From | Jason Low <> | Subject | [PATCH v2 4/5] MCS spinlocks: Micro-optimize osq_unlock() | Date | Mon, 14 Jul 2014 10:27:51 -0700 |
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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 <jason.low2@hp.com> --- kernel/locking/mcs_spinlock.c | 4 ++-- 1 files 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; -- 1.7.1
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