diff options
Diffstat (limited to 'kernel/rcu/Kconfig')
| -rw-r--r-- | kernel/rcu/Kconfig | 235 |
1 files changed, 170 insertions, 65 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 0ebe15a84985..b9b6bc55185d 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -8,6 +8,8 @@ menu "RCU Subsystem" config TREE_RCU bool default y if SMP + # Dynticks-idle tracking + select CONTEXT_TRACKING_IDLE help This option selects the RCU implementation that is designed for very large SMP system with hundreds or @@ -29,7 +31,7 @@ config PREEMPT_RCU config TINY_RCU bool - default y if !PREEMPTION && !SMP + default y if !PREEMPT_RCU && !SMP help This option selects the RCU implementation that is designed for UP systems from which real-time response @@ -51,56 +53,81 @@ config RCU_EXPERT 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 + default y if TINY_RCU help This option selects the single-CPU non-preemptible version of SRCU. config TREE_SRCU bool - default y if SRCU && !TINY_RCU + default y if !TINY_RCU help This option selects the full-fledged version of SRCU. +config NEED_SRCU_NMI_SAFE + def_bool HAVE_NMI && !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !TINY_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 FORCE_TASKS_RCU + bool "Force selection of TASKS_RCU" + depends on RCU_EXPERT + select TASKS_RCU + default n + help + This option force-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 in most cases. + +config NEED_TASKS_RCU + bool + default n + config TASKS_RCU - def_bool PREEMPTION + bool + default NEED_TASKS_RCU && (PREEMPTION || PREEMPT_AUTO) + select IRQ_WORK + +config FORCE_TASKS_RUDE_RCU + bool "Force selection of Tasks Rude RCU" + depends on RCU_EXPERT + select TASKS_RUDE_RCU + default n 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. + This option force-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. Not for manual selection in most cases. config TASKS_RUDE_RCU - def_bool 0 - 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. + bool + default n + select IRQ_WORK -config TASKS_TRACE_RCU - def_bool 0 +config FORCE_TASKS_TRACE_RCU + bool "Force selection of Tasks Trace RCU" + depends on RCU_EXPERT + select TASKS_TRACE_RCU + default n 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. + 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. Not for manual + selection in most cases. + +config TASKS_TRACE_RCU + bool + default n + select IRQ_WORK config RCU_STALL_COMMON def_bool TREE_RCU @@ -111,7 +138,7 @@ config RCU_STALL_COMMON making these warnings mandatory for the tree variants. config RCU_NEED_SEGCBLIST - def_bool ( TREE_RCU || TREE_SRCU ) + def_bool ( TREE_RCU || TREE_SRCU || TASKS_RCU_GENERIC ) config RCU_FANOUT int "Tree-based hierarchical RCU fanout value" @@ -135,10 +162,12 @@ config RCU_FANOUT config RCU_FANOUT_LEAF int "Tree-based hierarchical RCU leaf-level fanout value" - range 2 64 if 64BIT - range 2 32 if !64BIT + 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 + 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 @@ -166,28 +195,10 @@ config RCU_FANOUT_LEAF 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 + depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT + default y if PREEMPT_RT help This option boosts the priority of preempted RCU readers that block the current preemptible RCU grace period for too long. @@ -210,6 +221,20 @@ config RCU_BOOST_DELAY Accept the default if unsure. +config RCU_EXP_KTHREAD + bool "Perform RCU expedited work in a real-time kthread" + depends on RCU_BOOST && RCU_EXPERT + default !PREEMPT_RT && NR_CPUS <= 32 + help + Use this option to further reduce the latencies of expedited + grace periods at the expense of being more disruptive. + + This option is disabled by default on PREEMPT_RT=y kernels which + disable expedited grace periods after boot by unconditionally + setting rcupdate.rcu_normal_after_boot=1. + + Accept the default if unsure. + config RCU_NOCB_CPU bool "Offload RCU callback processing from boot-selected CPUs" depends on TREE_RCU @@ -219,24 +244,65 @@ config RCU_NOCB_CPU 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. + asymmetric multiprocessors. The price of this reduced jitter + is that the overhead of call_rcu() increases and that some + workloads will incur significant increases in context-switch + rates. + + 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 "p" for RCU-preempt (PREEMPTION kernels) + and "s" for RCU-sched (!PREEMPTION kernels). This option + also creates another kthread for each sqrt(nr_cpu_ids) CPUs + ("rcuog/N", where N is the first CPU in that group to come + online), which handles grace periods for its group. Nothing + prevents these kthreads 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. + + The sqrt(nr_cpu_ids) grouping may be overridden using the + rcutree.rcu_nocb_gp_stride kernel boot parameter. This can + be especially helpful for smaller numbers of CPUs, where + sqrt(nr_cpu_ids) can be a bit of a blunt instrument. + + Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. +config RCU_NOCB_CPU_DEFAULT_ALL + bool "Offload RCU callback processing from all CPUs by default" + depends on RCU_NOCB_CPU + default n + help + Use this option to offload callback processing from all CPUs + by default, in the absence of the rcu_nocbs or nohz_full boot + parameter. This also avoids the need to use any boot parameters + to achieve the effect of offloading all CPUs on boot. + + Say Y here if you want offload all CPUs by default on boot. + Say N here if you are unsure. + +config RCU_NOCB_CPU_CB_BOOST + bool "Offload RCU callback from real-time kthread" + depends on RCU_NOCB_CPU && RCU_BOOST + default y if PREEMPT_RT + help + Use this option to invoke offloaded callbacks as SCHED_FIFO + to avoid starvation by heavy SCHED_OTHER background load. + Of course, running as SCHED_FIFO during callback floods will + cause the rcuo[ps] kthreads to monopolize the CPU for hundreds + of milliseconds or more. Therefore, when enabling this option, + it is your responsibility to ensure that latency-sensitive + tasks either run with higher priority or run on some other CPU. + + Say Y here if you want to set RT priority for offloading kthreads. + Say N here if you are building a !PREEMPT_RT kernel and are unsure. + config TASKS_TRACE_RCU_READ_MB bool "Tasks Trace RCU readers use memory barriers in user and idle" - depends on RCU_EXPERT + depends on RCU_EXPERT && TASKS_TRACE_RCU default PREEMPT_RT || NR_CPUS < 8 help Use this option to further reduce the number of IPIs sent @@ -252,4 +318,43 @@ config TASKS_TRACE_RCU_READ_MB Say N here if you hate read-side memory barriers. Take the default if you are unsure. +config RCU_LAZY + bool "RCU callback lazy invocation functionality" + depends on RCU_NOCB_CPU + default n + help + To save power, batch RCU callbacks and flush after delay, memory + pressure, or callback list growing too big. + + Requires rcu_nocbs=all to be set. + + Use rcutree.enable_rcu_lazy=0 to turn it off at boot time. + +config RCU_LAZY_DEFAULT_OFF + bool "Turn RCU lazy invocation off by default" + depends on RCU_LAZY + default n + help + Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default + off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch + it back on. + +config RCU_DOUBLE_CHECK_CB_TIME + bool "RCU callback-batch backup time check" + depends on RCU_EXPERT + default n + help + Use this option to provide more precise enforcement of the + rcutree.rcu_resched_ns module parameter in situations where + a single RCU callback might run for hundreds of microseconds, + thus defeating the 32-callback batching used to amortize the + cost of the fine-grained but expensive local_clock() function. + + This option rounds rcutree.rcu_resched_ns up to the next + jiffy, and overrides the 32-callback batching if this limit + is exceeded. + + Say Y here if you need tighter callback-limit enforcement. + Say N here if you are unsure. + endmenu # "RCU Subsystem" |