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2023-12-08 01573e231f18eb2d99162747186f59511f56b64d

 kernel/kernel/rcu/Kconfig
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+# SPDX-License-Identifier: GPL-2.0-only
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 #
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 # RCU-related configuration options
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 #
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 config TREE_RCU
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 	bool
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-	default y if !PREEMPT && SMP
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+	default y if SMP
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 	help
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 	  This option selects the RCU implementation that is
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 	  designed for very large SMP system with hundreds or
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 config PREEMPT_RCU
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 	bool
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-	default y if PREEMPT
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+	default y if PREEMPTION
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+	select TREE_RCU
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 	help
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 	  This option selects the RCU implementation that is
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 	  designed for very large SMP systems with hundreds or
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 config TINY_RCU
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 	bool
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-	default y if !PREEMPT && !SMP
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+	default y if !PREEMPTION && !SMP
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 	help
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 	  This option selects the RCU implementation that is
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 	  designed for UP systems from which real-time response
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 	help
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 	  This option selects the full-fledged version of SRCU.
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-config TASKS_RCU
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-	def_bool PREEMPT
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+config TASKS_RCU_GENERIC
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+	def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU
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 	select SRCU
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+	help
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+	  This option enables generic infrastructure code supporting
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+	  task-based RCU implementations.  Not for manual selection.
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+
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+config TASKS_RCU
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+	def_bool PREEMPTION
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 	help
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 	  This option enables a task-based RCU implementation that uses
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 	  only voluntary context switch (not preemption!), idle, and
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-	  user-mode execution as quiescent states.
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+	  user-mode execution as quiescent states.  Not for manual selection.
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+
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+config TASKS_RUDE_RCU
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+	def_bool 0
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+	select IRQ_WORK
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+	help
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+	  This option enables a task-based RCU implementation that uses
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+	  only context switch (including preemption) and user-mode
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+	  execution as quiescent states.  It forces IPIs and context
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+	  switches on all online CPUs, including idle ones, so use
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+	  with caution.
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+
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+config TASKS_TRACE_RCU
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+	def_bool 0
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+	help
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+	  This option enables a task-based RCU implementation that uses
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+	  explicit rcu_read_lock_trace() read-side markers, and allows
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+	  these readers to appear in the idle loop as well as on the CPU
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+	  hotplug code paths.  It can force IPIs on online CPUs, including
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+	  idle ones, so use with caution.
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 config RCU_STALL_COMMON
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-	def_bool ( TREE_RCU || PREEMPT_RCU )
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+	def_bool TREE_RCU
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 	help
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 	  This option enables RCU CPU stall code that is common between
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 	  the TINY and TREE variants of RCU.  The purpose is to allow
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 	  making these warnings mandatory for the tree variants.
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 config RCU_NEED_SEGCBLIST
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-	def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
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-
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-config CONTEXT_TRACKING
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-       bool
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-
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-config CONTEXT_TRACKING_FORCE
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-	bool "Force context tracking"
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-	depends on CONTEXT_TRACKING
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-	default y if !NO_HZ_FULL
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-	help
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-	  The major pre-requirement for full dynticks to work is to
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-	  support the context tracking subsystem. But there are also
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-	  other dependencies to provide in order to make the full
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-	  dynticks working.
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-	  This option stands for testing when an arch implements the
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-	  context tracking backend but doesn't yet fullfill all the
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-	  requirements to make the full dynticks feature working.
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-	  Without the full dynticks, there is no way to test the support
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-	  for context tracking and the subsystems that rely on it: RCU
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-	  userspace extended quiescent state and tickless cputime
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-	  accounting. This option copes with the absence of the full
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-	  dynticks subsystem by forcing the context tracking on all
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-	  CPUs in the system.
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-	  Say Y only if you're working on the development of an
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-	  architecture backend for the context tracking.
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-
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-	  Say N otherwise, this option brings an overhead that you
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-	  don't want in production.
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-
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+	def_bool ( TREE_RCU || TREE_SRCU )
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 config RCU_FANOUT
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 	int "Tree-based hierarchical RCU fanout value"
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 	range 2 64 if 64BIT
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 	range 2 32 if !64BIT
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-	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
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+	depends on TREE_RCU && RCU_EXPERT
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 	default 64 if 64BIT
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 	default 32 if !64BIT
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 	help
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 config RCU_FANOUT_LEAF
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 	int "Tree-based hierarchical RCU leaf-level fanout value"
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-	range 2 64 if 64BIT
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-	range 2 32 if !64BIT
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-	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
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-	default 16
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+	range 2 64 if 64BIT && !RCU_STRICT_GRACE_PERIOD
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+	range 2 32 if !64BIT && !RCU_STRICT_GRACE_PERIOD
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+	range 2 3 if RCU_STRICT_GRACE_PERIOD
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+	depends on TREE_RCU && RCU_EXPERT
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+	default 16 if !RCU_STRICT_GRACE_PERIOD
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+	default 2 if RCU_STRICT_GRACE_PERIOD
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 	help
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 	  This option controls the leaf-level fanout of hierarchical
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 	  implementations of RCU, and allows trading off cache misses
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 config RCU_FAST_NO_HZ
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 	bool "Accelerate last non-dyntick-idle CPU's grace periods"
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-	depends on NO_HZ_COMMON && SMP && RCU_EXPERT && !PREEMPT_RT_FULL
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+	depends on NO_HZ_COMMON && SMP && RCU_EXPERT
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 	default n
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 	help
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 	  This option permits CPUs to enter dynticks-idle state even if
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 config RCU_BOOST
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 	bool "Enable RCU priority boosting"
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-	depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT_FULL
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-	default y if PREEMPT_RT_FULL
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+	depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT
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+	default y if PREEMPT_RT
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 	help
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 	  This option boosts the priority of preempted RCU readers that
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 	  block the current preemptible RCU grace period for too long.
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 	  This option also prevents heavy loads from blocking RCU
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-	  callback invocation for all flavors of RCU.
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+	  callback invocation.
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 	  Say Y here if you are working with real-time apps or heavy loads
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 	  Say N here if you are unsure.
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 config RCU_NOCB_CPU
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 	bool "Offload RCU callback processing from boot-selected CPUs"
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-	depends on TREE_RCU || PREEMPT_RCU
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+	depends on TREE_RCU
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 	depends on RCU_EXPERT || NO_HZ_FULL
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 	default n
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 	help
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 	  callback invocation to energy-efficient CPUs in battery-powered
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 	  asymmetric multiprocessors.
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-	  This option offloads callback invocation from the set of
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-	  CPUs specified at boot time by the rcu_nocbs parameter.
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-	  For each such CPU, a kthread ("rcuox/N") will be created to
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-	  invoke callbacks, where the "N" is the CPU being offloaded,
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-	  and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
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-	  "s" for RCU-sched.  Nothing prevents this kthread from running
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+	  This option offloads callback invocation from the set of CPUs
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+	  specified at boot time by the rcu_nocbs parameter.  For each
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+	  such CPU, a kthread ("rcuox/N") will be created to invoke
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+	  callbacks, where the "N" is the CPU being offloaded, and where
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+	  the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched
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+	  (!PREEMPTION kernels).  Nothing prevents this kthread from running
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 	  on the specified CPUs, but (1) the kthreads may be preempted
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 	  between each callback, and (2) affinity or cgroups can be used
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 	  to force the kthreads to run on whatever set of CPUs is desired.
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 	  Say Y here if you want to help to debug reduced OS jitter.
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 	  Say N here if you are unsure.
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+config TASKS_TRACE_RCU_READ_MB
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+	bool "Tasks Trace RCU readers use memory barriers in user and idle"
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+	depends on RCU_EXPERT
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+	default PREEMPT_RT || NR_CPUS < 8
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+	help
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+	  Use this option to further reduce the number of IPIs sent
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+	  to CPUs executing in userspace or idle during tasks trace
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+	  RCU grace periods.  Given that a reasonable setting of
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+	  the rcupdate.rcu_task_ipi_delay kernel boot parameter
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+	  eliminates such IPIs for many workloads, proper setting
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+	  of this Kconfig option is important mostly for aggressive
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+	  real-time installations and for battery-powered devices,
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+	  hence the default chosen above.
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+	  Say Y here if you hate IPIs.
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+	  Say N here if you hate read-side memory barriers.
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+	  Take the default if you are unsure.
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+
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 endmenu # "RCU Subsystem"