213 строки
7.3 KiB
Plaintext
213 строки
7.3 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
|
|
#
|
|
# RCU-related configuration options
|
|
#
|
|
|
|
menu "RCU Subsystem"
|
|
|
|
config TREE_RCU
|
|
bool
|
|
default y if !PREEMPTION && 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
|
|
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
|
|
def_bool PREEMPTION
|
|
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 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.
|
|
|
|
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 "p" for RCU-preempt (PREEMPT kernels) and "s" for RCU-sched
|
|
(!PREEMPT 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.
|
|
|
|
endmenu # "RCU Subsystem"
|