locking/mcs: Micro-optimize the MCS code, add extra comments

Remove unnecessary operation to assign locked status to 1 if lock is
acquired without contention. Lock status will not be checked by lock
holder again once it is acquired and any lock
contenders will not be looking at the lock holder's lock status.

Make the cmpxchg(lock, node, NULL) == node check in mcs_spin_unlock()
likely() as it is likely that a race did not occur most of the time.

Also add in more comments describing how the local node is used in MCS locks.

Reviewed-by: Paul E. McKenney <[email protected]>
Reviewed-by: Tim Chen <[email protected]>
Signed-off-by: Jason Low <[email protected]>
Signed-off-by: Tim Chen <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: http://lkml.kernel.org/r/1390347365.3138.64.camel@schen9-DESK
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions