#
  # RCU-related configuration options
  #
  
  menu "RCU Subsystem"
  
  config TREE_RCU
  	bool
  	default y if !PREEMPT && SMP
  	help
  	  This option selects the RCU implementation that is
  	  designed for very large SMP system with hundreds or
  	  thousands of CPUs.  It also scales down nicely to
  	  smaller systems.
  
  config PREEMPT_RCU
  	bool
  	default y if PREEMPT
  	help
  	  This option selects the RCU implementation that is
  	  designed for very large SMP systems with hundreds or
  	  thousands of CPUs, but for which real-time response
  	  is also required.  It also scales down nicely to
  	  smaller systems.
  
  	  Select this option if you are unsure.
  
  config TINY_RCU
  	bool
  	default y if !PREEMPT && !SMP
  	help
  	  This option selects the RCU implementation that is
  	  designed for UP systems from which real-time response
  	  is not required.  This option greatly reduces the
  	  memory footprint of RCU.
  
  config RCU_EXPERT
  	bool "Make expert-level adjustments to RCU configuration"
  	default n
  	help
  	  This option needs to be enabled if you wish to make
  	  expert-level adjustments to RCU configuration.  By default,
  	  no such adjustments can be made, which has the often-beneficial
  	  side-effect of preventing "make oldconfig" from asking you all
  	  sorts of detailed questions about how you would like numerous
  	  obscure RCU options to be set up.
  
  	  Say Y if you need to make expert-level adjustments to RCU.
  
  	  Say N if you are unsure.
  
  config SRCU
  	bool
  	help
  	  This option selects the sleepable version of RCU. This version
  	  permits arbitrary sleeping or blocking within RCU read-side critical
  	  sections.
  
  config TINY_SRCU
  	bool
  	default y if SRCU && TINY_RCU
  	help
  	  This option selects the single-CPU non-preemptible version of SRCU.
  
  config TREE_SRCU
  	bool
  	default y if SRCU && !TINY_RCU
  	help
  	  This option selects the full-fledged version of SRCU.
  
  config TASKS_RCU

  	def_bool PREEMPT

  	select SRCU
  	help
  	  This option enables a task-based RCU implementation that uses
  	  only voluntary context switch (not preemption!), idle, and
  	  user-mode execution as quiescent states.
  
  config RCU_STALL_COMMON

  	def_bool ( TREE_RCU || PREEMPT_RCU )

  	help
  	  This option enables RCU CPU stall code that is common between
  	  the TINY and TREE variants of RCU.  The purpose is to allow
  	  the tiny variants to disable RCU CPU stall warnings, while
  	  making these warnings mandatory for the tree variants.
  
  config RCU_NEED_SEGCBLIST
  	def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
  
  config CONTEXT_TRACKING
         bool
  
  config CONTEXT_TRACKING_FORCE
  	bool "Force context tracking"
  	depends on CONTEXT_TRACKING
  	default y if !NO_HZ_FULL
  	help
  	  The major pre-requirement for full dynticks to work is to
  	  support the context tracking subsystem. But there are also
  	  other dependencies to provide in order to make the full
  	  dynticks working.
  
  	  This option stands for testing when an arch implements the
  	  context tracking backend but doesn't yet fullfill all the
  	  requirements to make the full dynticks feature working.
  	  Without the full dynticks, there is no way to test the support
  	  for context tracking and the subsystems that rely on it: RCU
  	  userspace extended quiescent state and tickless cputime
  	  accounting. This option copes with the absence of the full
  	  dynticks subsystem by forcing the context tracking on all
  	  CPUs in the system.
  
  	  Say Y only if you're working on the development of an
  	  architecture backend for the context tracking.
  
  	  Say N otherwise, this option brings an overhead that you
  	  don't want in production.
  
  
  config RCU_FANOUT
  	int "Tree-based hierarchical RCU fanout value"
  	range 2 64 if 64BIT
  	range 2 32 if !64BIT
  	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
  	default 64 if 64BIT
  	default 32 if !64BIT
  	help
  	  This option controls the fanout of hierarchical implementations
  	  of RCU, allowing RCU to work efficiently on machines with
  	  large numbers of CPUs.  This value must be at least the fourth
  	  root of NR_CPUS, which allows NR_CPUS to be insanely large.
  	  The default value of RCU_FANOUT should be used for production
  	  systems, but if you are stress-testing the RCU implementation
  	  itself, small RCU_FANOUT values allow you to test large-system
  	  code paths on small(er) systems.
  
  	  Select a specific number if testing RCU itself.
  	  Take the default if unsure.
  
  config RCU_FANOUT_LEAF
  	int "Tree-based hierarchical RCU leaf-level fanout value"
  	range 2 64 if 64BIT
  	range 2 32 if !64BIT
  	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
  	default 16
  	help
  	  This option controls the leaf-level fanout of hierarchical
  	  implementations of RCU, and allows trading off cache misses
  	  against lock contention.  Systems that synchronize their
  	  scheduling-clock interrupts for energy-efficiency reasons will
  	  want the default because the smaller leaf-level fanout keeps
  	  lock contention levels acceptably low.  Very large systems
  	  (hundreds or thousands of CPUs) will instead want to set this
  	  value to the maximum value possible in order to reduce the
  	  number of cache misses incurred during RCU's grace-period
  	  initialization.  These systems tend to run CPU-bound, and thus
  	  are not helped by synchronized interrupts, and thus tend to
  	  skew them, which reduces lock contention enough that large
  	  leaf-level fanouts work well.  That said, setting leaf-level
  	  fanout to a large number will likely cause problematic
  	  lock contention on the leaf-level rcu_node structures unless
  	  you boot with the skew_tick kernel parameter.
  
  	  Select a specific number if testing RCU itself.
  
  	  Select the maximum permissible value for large systems, but
  	  please understand that you may also need to set the skew_tick
  	  kernel boot parameter to avoid contention on the rcu_node
  	  structure's locks.
  
  	  Take the default if unsure.
  
  config RCU_FAST_NO_HZ
  	bool "Accelerate last non-dyntick-idle CPU's grace periods"
  	depends on NO_HZ_COMMON && SMP && RCU_EXPERT
  	default n
  	help
  	  This option permits CPUs to enter dynticks-idle state even if
  	  they have RCU callbacks queued, and prevents RCU from waking
  	  these CPUs up more than roughly once every four jiffies (by
  	  default, you can adjust this using the rcutree.rcu_idle_gp_delay
  	  parameter), thus improving energy efficiency.  On the other
  	  hand, this option increases the duration of RCU grace periods,
  	  for example, slowing down synchronize_rcu().
  
  	  Say Y if energy efficiency is critically important, and you
  	  	don't care about increased grace-period durations.
  
  	  Say N if you are unsure.
  
  config RCU_BOOST
  	bool "Enable RCU priority boosting"
  	depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
  	default n
  	help
  	  This option boosts the priority of preempted RCU readers that
  	  block the current preemptible RCU grace period for too long.
  	  This option also prevents heavy loads from blocking RCU
  	  callback invocation for all flavors of RCU.
  
  	  Say Y here if you are working with real-time apps or heavy loads
  	  Say N here if you are unsure.
  
  config RCU_BOOST_DELAY
  	int "Milliseconds to delay boosting after RCU grace-period start"
  	range 0 3000
  	depends on RCU_BOOST
  	default 500
  	help
  	  This option specifies the time to wait after the beginning of
  	  a given grace period before priority-boosting preempted RCU
  	  readers blocking that grace period.  Note that any RCU reader
  	  blocking an expedited RCU grace period is boosted immediately.
  
  	  Accept the default if unsure.
  
  config RCU_NOCB_CPU
  	bool "Offload RCU callback processing from boot-selected CPUs"
  	depends on TREE_RCU || PREEMPT_RCU
  	depends on RCU_EXPERT || NO_HZ_FULL
  	default n
  	help
  	  Use this option to reduce OS jitter for aggressive HPC or
  	  real-time workloads.	It can also be used to offload RCU
  	  callback invocation to energy-efficient CPUs in battery-powered
  	  asymmetric multiprocessors.
  
  	  This option offloads callback invocation from the set of
  	  CPUs specified at boot time by the rcu_nocbs parameter.
  	  For each such CPU, a kthread ("rcuox/N") will be created to
  	  invoke callbacks, where the "N" is the CPU being offloaded,
  	  and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
  	  "s" for RCU-sched.  Nothing prevents this kthread from running
  	  on the specified CPUs, but (1) the kthreads may be preempted
  	  between each callback, and (2) affinity or cgroups can be used
  	  to force the kthreads to run on whatever set of CPUs is desired.
  
  	  Say Y here if you want to help to debug reduced OS jitter.
  	  Say N here if you are unsure.
  
  endmenu # "RCU Subsystem"