diff options
Diffstat (limited to 'kernel/rcu/Kconfig')
| -rw-r--r-- | kernel/rcu/Kconfig | 258 |
1 files changed, 258 insertions, 0 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig new file mode 100644 index 000000000..cd6e11403 --- /dev/null +++ b/kernel/rcu/Kconfig @@ -0,0 +1,258 @@ +# SPDX-License-Identifier: GPL-2.0-only +# +# RCU-related configuration options +# + +menu "RCU Subsystem" + +config TREE_RCU + bool + default y if 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 PREEMPTION + select TREE_RCU + 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 !PREEMPTION && !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_GENERIC + def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU + select SRCU + help + This option enables generic infrastructure code supporting + task-based RCU implementations. Not for manual selection. + +config TASKS_RCU + def_bool PREEMPTION + 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. Not for manual selection. + +config TASKS_RUDE_RCU + def_bool 0 + select IRQ_WORK + help + This option enables a task-based RCU implementation that uses + only context switch (including preemption) and user-mode + execution as quiescent states. It forces IPIs and context + switches on all online CPUs, including idle ones, so use + with caution. + +config TASKS_TRACE_RCU + def_bool 0 + help + This option enables a task-based RCU implementation that uses + explicit rcu_read_lock_trace() read-side markers, and allows + these readers to appear in the idle loop as well as on the CPU + hotplug code paths. It can force IPIs on online CPUs, including + idle ones, so use with caution. + +config RCU_STALL_COMMON + def_bool TREE_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 || TREE_SRCU ) + +config RCU_FANOUT + int "Tree-based hierarchical RCU fanout value" + range 2 64 if 64BIT + range 2 32 if !64BIT + depends on TREE_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 && !RCU_STRICT_GRACE_PERIOD + range 2 32 if !64BIT && !RCU_STRICT_GRACE_PERIOD + range 2 3 if RCU_STRICT_GRACE_PERIOD + depends on TREE_RCU && RCU_EXPERT + default 16 if !RCU_STRICT_GRACE_PERIOD + default 2 if RCU_STRICT_GRACE_PERIOD + 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. + + 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 + 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 "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched + (!PREEMPTION kernels). 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. + +config TASKS_TRACE_RCU_READ_MB + bool "Tasks Trace RCU readers use memory barriers in user and idle" + depends on RCU_EXPERT + default PREEMPT_RT || NR_CPUS < 8 + help + Use this option to further reduce the number of IPIs sent + to CPUs executing in userspace or idle during tasks trace + RCU grace periods. Given that a reasonable setting of + the rcupdate.rcu_task_ipi_delay kernel boot parameter + eliminates such IPIs for many workloads, proper setting + of this Kconfig option is important mostly for aggressive + real-time installations and for battery-powered devices, + hence the default chosen above. + + Say Y here if you hate IPIs. + Say N here if you hate read-side memory barriers. + Take the default if you are unsure. + +endmenu # "RCU Subsystem" |