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authorJason Low <jason.low2@hp.com>2014-07-14 10:27:51 -0700
committerIngo Molnar <mingo@kernel.org>2014-07-16 13:28:06 +0200
commit33ecd2083a9560fbc1ef1b1279ef3ecb4c012a4f (patch)
treed3c7834d2f4140fb64d80c7560513374ac1d5ca8 /kernel
parent4d9d951e6b5df85ccfca2c5bd8b4f5c71d256b65 (diff)
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 <jason.low2@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Scott Norton <scott.norton@hp.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Waiman Long <waiman.long@hp.com> Cc: Davidlohr Bueso <davidlohr@hp.com> Cc: Rik van Riel <riel@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1405358872-3732-5-git-send-email-jason.low2@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/locking/mcs_spinlock.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/locking/mcs_spinlock.c b/kernel/locking/mcs_spinlock.c
index 32fc16c0a54..be9ee1559fc 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;