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authorJason Low <jason.low2@hp.com>2014-07-14 10:27:49 -0700
committerIngo Molnar <mingo@kernel.org>2014-07-16 13:28:04 +0200
commit90631822c5d307b5410500806e8ac3e63928aa3e (patch)
treecb1d12a3fe3b1bc5ab8816b32a078430bb42bb24 /kernel/locking/mutex.c
parent046a619d8e9746fa4c0e29e8c6b78e16efc008a8 (diff)
locking/spinlocks/mcs: Convert osq lock to atomic_t to reduce overhead
The cancellable MCS spinlock is currently used to queue threads that are doing optimistic spinning. It uses per-cpu nodes, where a thread obtaining the lock would access and queue the local node corresponding to the CPU that it's running on. Currently, the cancellable MCS lock is implemented by using pointers to these nodes. In this patch, instead of operating on pointers to the per-cpu nodes, we store the CPU numbers in which the per-cpu nodes correspond to in atomic_t. A similar concept is used with the qspinlock. By operating on the CPU # of the nodes using atomic_t instead of pointers to those nodes, this can reduce the overhead of the cancellable MCS spinlock by 32 bits (on 64 bit systems). 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> Cc: Chris Mason <clm@fb.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Josef Bacik <jbacik@fusionio.com> Link: http://lkml.kernel.org/r/1405358872-3732-3-git-send-email-jason.low2@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/mutex.c')
-rw-r--r--kernel/locking/mutex.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index bc73d33c6760..d9b313906caa 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -60,7 +60,7 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
INIT_LIST_HEAD(&lock->wait_list);
mutex_clear_owner(lock);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- lock->osq = NULL;
+ atomic_set(&lock->osq.tail, OSQ_UNLOCKED_VAL);
#endif
debug_mutex_init(lock, name, key);