[PATCH tip/core/rcu 0/5] Fix for cond_resched performance regression

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

Hello!

This series contains changes to address the performance regressions
introduced by commit ac1bea85781e (Make cond_resched() report RCU
quiescent states), which was in turn fixing a problem where tasks looping
in the kernel could delay RCU grace periods.  The changes in this series
are as follows:

1.	Reduce the overhead of checking added to cond_resched() and friends.

2.	Add a new cond_resched_rcu_qs() to provide RCU quiescent states
	even if cond_resched() should stop doing so.

3.	Add a new RCU_COND_RESCHED_QS to prevent cond_resched() from
	reporting RCU quiescent states.

4.	Prevent rcutorture testing from reporting spurious RCU CPU stall
	warnings, and also to test RCU_COND_RESCHED_QS.

5.	Provides a boot/sysfs rcutree.jiffies_till_cond_resched_qs
	parameter to replace the magic "7".

							Thanx, Paul

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

 b/Documentation/kernel-parameters.txt                   |    7 +
 b/fs/file.c                                             |    2 
 b/include/linux/rcupdate.h                              |   35 -----
 b/include/linux/rcutiny.h                               |   17 ++
 b/include/linux/rcutree.h                               |   44 ++++++
 b/init/Kconfig                                          |   26 +++
 b/kernel/rcu/rcutorture.c                               |    4 
 b/kernel/rcu/tree.c                                     |  111 +++++++++++++---
 b/kernel/rcu/tree.h                                     |    6 
 b/kernel/rcu/tree_plugin.h                              |    4 
 b/kernel/rcu/update.c                                   |   18 --
 b/mm/mlock.c                                            |    2 
 b/tools/testing/selftests/rcutorture/configs/rcu/TREE01 |    1 
 13 files changed, 201 insertions(+), 76 deletions(-)