Expedited-grace-period changes for 4.5

Hello!

This series contains follow-on cleanup changes to RCU's expedited grace-period functionality. The patches in this series are as follows:

1. Short-circuit synchronize_sched_expedited() if there is only one CPU.

2. Update comment to clarify the role of ->expmaskinitnext.

3. Separate concerns by moving smp_mb() from rcu_seq_snap() to

	rcu_exp_gp_seq_snap().

4. Safe a few lines of code by inverting the sense of
sync_rcu_exp_select_cpus() "if" statement.

5. Reduce expedited GP memory contention via per-CPU variables.

6. Get rid of (some) empty stall-warning messages by resolving
stall-warning ties.

7. Add more diagnostics to expedited stall warning messages.

8. Add rcu_normal kernel parameter to suppress expediting for
the benefit of aggressive real-time systems.

9-10. Allow expedited grace periods to be disabled just before init
is spawned, allowing them to speed up boot without interfering with run-time real-time workloads.

11. Remove TINY_RCU bloat from pointless (to TINY_RCU) boot parameters.

Changes since v1:

o Add patch 11 removing TINY_RCU bloat.

o Get cover letter and patches correctly associated. :-/

Thanx, Paul

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

 Documentation/kernel-parameters.txt |   37 ++++++++++++----
 include/linux/rcupdate.h            |   15 ++++++
 init/main.c                         |    2 
 kernel/ksysfs.c                     |   26 ++++++++++-
 kernel/rcu/srcu.c                   |    2 
 kernel/rcu/tree.c                   |   79 +++++++++++++++++++++++-------------
 kernel/rcu/tree.h                   |   10 ++--
 kernel/rcu/tree_plugin.h            |    6 ++
 kernel/rcu/tree_trace.c             |   18 +++++---
 kernel/rcu/update.c                 |   24 +++++++++-
 10 files changed, 165 insertions(+), 54 deletions(-)