[PATCH RFC tip/core/rcu 0/14] Rework expedited grace periods

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello!

This RFC series reworks the handling of expedited grace periods, eliminating
the previous use of try_stop_cpus(), improving scalability, and adding
an RCU CPU stall-warning capability.  This series is as follows:

1.	Replace try_stop_cpus() with stop_one_cpu(), courtesy of
	Peter Zijlstra.

2.	Improve counter handling to more efficiently detect that some
	other task has already done the required work.

3.	Replace synchronize_sched_expedited()'s polling loop with
	funnel locking.

4.	Replace stop_one_cpu() with stop_one_cpu_nowait() to avoid the
	latency hit from #1 above, also courtesy of Peter Zijlstra.

5.	Abstract the counter handling.

6.	Apply the newly abstracted counter handling to
	synchronize_rcu_expedited().

7.	Abstract the funnel locking.

8.	Fix a stupid type error in synchronize_sched_expedited().

9.	Replace synchronize_rcu_expedited()'s polling with the newly
	abstracted funnel locking.

10.	Apply the abstracted counter handling to _rcu_barrier().

11.	Consolidate the last expedited open-coded expedited memory barrier
	into the counter handling.

12.	Extend the funnel locking to the rcu_data structure in order to
	further increase scalability.

13.	Add stall warnings to synchronize_sched_expedited().

14.	Document the newly added stall warnings.

							Thanx, Paul

------------------------------------------------------------------------

 b/Documentation/RCU/stallwarn.txt |   17 +
 b/include/trace/events/rcu.h      |    1 
 b/kernel/rcu/tree.c               |  581 +++++++++++++++++++-------------------
 b/kernel/rcu/tree.h               |   31 +-
 b/kernel/rcu/tree_plugin.h        |   53 +--
 b/kernel/rcu/tree_trace.c         |   25 -
 6 files changed, 369 insertions(+), 339 deletions(-)