[PATCH RFC tip/core/rcu 0/2] Real-time elimination of RCU_SOFTIRQ

[Paul E. McKenney]

Hello!

This series is an early posting of code to add a boot-time option to
move RCU's softirq processing to per-CPU kthreads.  This is not done
by default for performance reasons, nor are these reasons theoretical.
In fact, earlier attempts to do just this were not met with silence.

The patches are as follows:

1.	Enable elimination of Tree-RCU softirq processing via a new
	rcutree.use_softirq kernel boot parameter.  This defaults to 1,
	so boot with "rcutree.use_softirq=0" to move RCU_SOFTIRQ work
	to the rcuc kthreads.  Courtesy of Sebastian Andrzej Siewior.

2.	Improve wakeup-safety checks in rcu_read_unlock_special(),
	thus allowing both rcuc kthreads and reasonably snappy
	expedited RCU grace periods.

							Thanx, Paul

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

 Documentation/admin-guide/kernel-parameters.txt |    6 
 include/linux/sched.h                           |    2 
 kernel/rcu/tree.c                               |  138 +++++++++++++++++++--
 kernel/rcu/tree.h                               |    2 
 kernel/rcu/tree_plugin.h                        |  153 ++++--------------------
 5 files changed, 161 insertions(+), 140 deletions(-)