[PATCH tip/core/rcu 0/15] Improvements to rcu_barrier() and RT response on big systems

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

Hello!

This patch series contains improvements to the rcu_barrier() family of
primitives and to latency for large systems.  These are in a single
series due to conflicts that would otherwise occur.  The individual
patches are as follows:

1.	Allow the value for RCU_FANOUT_LEAF to be increased (but not
	decreased!) via a boot-time parameter, in turn allowing a
	default kernel build to be adjusted for low RCU grace-period
	initialization latency on a large system.
2.	Work around the new default NR_CPUS=4096 by checking the
	boot-time-computed nr_cpu_ids, allowing this to override
	NR_CPUS.  This again reduces RCU grace-period initialization
	latency for kernels built with large NR_CPUS running on small
	systems.
3.	Shrink a macro argument to keep lines under 80 characters.
4.	Add a pointer in the rcu_state structure to the corresponding
	member of the call_rcu() family of functions in preparation
	for increasing rcu_barrier() concurrency.
5.	Move _rcu_barrier()'s rcu_head structures to the per-CPU
	per-RCU-flavor rcu_data structures so that different flavors
	of rcu_barrier() do not need to contend for the rcu_head
	structures.
6.	Move rcu_barrier()'s rcu_barrier_cpu_count global variable to
	a new ->barrier_cpu_count field in the rcu_state structure, so
	that different flavors of rcu_barrier() do not need to contend
	for this variable.
7.	Move rcu_barrier()'s rcu_barrier_completion global variable to
	a new ->barrier_completion field in the rcu_state structure, so
	that different flavors of rcu_barrier() do not need to contend
	for this variable.
8.	Move rcu_barrier()'s rcu_barrier_mutex global variable to
	a new ->barrier_mutex field in the rcu_state structure, so that
	different flavors of rcu_barrier() do not need to contend for
	this variable.
9.	Introduce counter scheme to allow multiple concurrent executions
	of a given flavor of rcu_barrier() to share work.
10.	Add event tracing for _rcu_barrier().
11.	Add debugfs tracing for _rcu_barrier().
12.	Remove unnecessary per-CPU variable argument from
	__rcu_process_callbacks().
13.	Introduce for_each_rcu_flavor() iterator and use it.  This provides
	a nicer way to iterate through the RCU flavors to do per-flavor
	processing.
14.	Apply the for_each_rcu_flavor() iterator to debugfs tracing.
15.	Remove dead-code gcc helper from code that is no longer ever dead.

							Thanx, Paul

 b/Documentation/kernel-parameters.txt |    4 
 b/include/trace/events/rcu.h          |   45 +++++++
 b/kernel/rcutree.c                    |   97 +++++++++++++--
 b/kernel/rcutree.h                    |   23 ++-
 b/kernel/rcutree_plugin.h             |    4 
 b/kernel/rcutree_trace.c              |    2 
 kernel/rcutree.c                      |  213 +++++++++++++++++++++-------------
 kernel/rcutree.h                      |   22 ++-
 kernel/rcutree_plugin.h               |  126 --------------------
 kernel/rcutree_trace.c                |  134 ++++++++++++---------
 10 files changed, 379 insertions(+), 291 deletions(-)