locking/mcs: Allow architectures to hook in to contended paths
locking/mcs: Allow architectures to hook in to contended paths

When contended, architectures may be able to reduce the polling overhead
in ways which aren't expressible using a simple relax() primitive.

This patch allows architectures to hook into the mcs_{lock,unlock}
functions for the contended cases only.

Reviewed-by: Paul E. McKenney <1e0ce936bb9b355d257bf5790d2513c3f28be22b@linux.vnet.ibm.com>
Signed-off-by: Will Deacon <b913f13ef92ac157955c954ccaaff7be065faba4@arm.com>
Signed-off-by: Tim Chen <695db642e8bc2a781029b5690bc796db9446cc2f@linux.intel.com>
Signed-off-by: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Cc: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Link: 8a7fc8a9f1d391972daa693299bdd2176ebc90e7@schen9-DESK
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs