Linux/kernel/rcu/Kconfig

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Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

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1 # SPDX-License-Identifier: GPL-2.0-only 1 # SPDX-License-Identifier: GPL-2.0-only 2 # 2 # 3 # RCU-related configuration options 3 # RCU-related configuration options 4 # 4 # 5 5 6 menu "RCU Subsystem" 6 menu "RCU Subsystem" 7 7 8 config TREE_RCU 8 config TREE_RCU 9 bool 9 bool 10 default y if SMP 10 default y if SMP 11 # Dynticks-idle tracking << 12 select CONTEXT_TRACKING_IDLE << 13 help 11 help 14 This option selects the RCU implemen 12 This option selects the RCU implementation that is 15 designed for very large SMP system w 13 designed for very large SMP system with hundreds or 16 thousands of CPUs. It also scales d 14 thousands of CPUs. It also scales down nicely to 17 smaller systems. 15 smaller systems. 18 16 19 config PREEMPT_RCU 17 config PREEMPT_RCU 20 bool 18 bool 21 default y if PREEMPTION 19 default y if PREEMPTION 22 select TREE_RCU 20 select TREE_RCU 23 help 21 help 24 This option selects the RCU implemen 22 This option selects the RCU implementation that is 25 designed for very large SMP systems 23 designed for very large SMP systems with hundreds or 26 thousands of CPUs, but for which rea 24 thousands of CPUs, but for which real-time response 27 is also required. It also scales do 25 is also required. It also scales down nicely to 28 smaller systems. 26 smaller systems. 29 27 30 Select this option if you are unsure 28 Select this option if you are unsure. 31 29 32 config TINY_RCU 30 config TINY_RCU 33 bool 31 bool 34 default y if !PREEMPT_RCU && !SMP !! 32 default y if !PREEMPTION && !SMP 35 help 33 help 36 This option selects the RCU implemen 34 This option selects the RCU implementation that is 37 designed for UP systems from which r 35 designed for UP systems from which real-time response 38 is not required. This option greatl 36 is not required. This option greatly reduces the 39 memory footprint of RCU. 37 memory footprint of RCU. 40 38 41 config RCU_EXPERT 39 config RCU_EXPERT 42 bool "Make expert-level adjustments to 40 bool "Make expert-level adjustments to RCU configuration" 43 default n 41 default n 44 help 42 help 45 This option needs to be enabled if y 43 This option needs to be enabled if you wish to make 46 expert-level adjustments to RCU conf 44 expert-level adjustments to RCU configuration. By default, 47 no such adjustments can be made, whi 45 no such adjustments can be made, which has the often-beneficial 48 side-effect of preventing "make oldc 46 side-effect of preventing "make oldconfig" from asking you all 49 sorts of detailed questions about ho 47 sorts of detailed questions about how you would like numerous 50 obscure RCU options to be set up. 48 obscure RCU options to be set up. 51 49 52 Say Y if you need to make expert-lev 50 Say Y if you need to make expert-level adjustments to RCU. 53 51 54 Say N if you are unsure. 52 Say N if you are unsure. 55 53 >> 54 config SRCU >> 55 bool >> 56 help >> 57 This option selects the sleepable version of RCU. This version >> 58 permits arbitrary sleeping or blocking within RCU read-side critical >> 59 sections. >> 60 56 config TINY_SRCU 61 config TINY_SRCU 57 bool 62 bool 58 default y if TINY_RCU !! 63 default y if SRCU && TINY_RCU 59 help 64 help 60 This option selects the single-CPU n 65 This option selects the single-CPU non-preemptible version of SRCU. 61 66 62 config TREE_SRCU 67 config TREE_SRCU 63 bool 68 bool 64 default y if !TINY_RCU !! 69 default y if SRCU && !TINY_RCU 65 help 70 help 66 This option selects the full-fledged 71 This option selects the full-fledged version of SRCU. 67 72 68 config NEED_SRCU_NMI_SAFE << 69 def_bool HAVE_NMI && !ARCH_HAS_NMI_SAF << 70 << 71 config TASKS_RCU_GENERIC << 72 def_bool TASKS_RCU || TASKS_RUDE_RCU | << 73 help << 74 This option enables generic infrastr << 75 task-based RCU implementations. Not << 76 << 77 config FORCE_TASKS_RCU << 78 bool "Force selection of TASKS_RCU" << 79 depends on RCU_EXPERT << 80 select TASKS_RCU << 81 default n << 82 help << 83 This option force-enables a task-bas << 84 that uses only voluntary context swi << 85 idle, and user-mode execution as qui << 86 manual selection in most cases. << 87 << 88 config NEED_TASKS_RCU << 89 bool << 90 default n << 91 << 92 config TASKS_RCU 73 config TASKS_RCU 93 bool !! 74 def_bool PREEMPTION 94 default NEED_TASKS_RCU && (PREEMPTION !! 75 select SRCU 95 select IRQ_WORK << 96 << 97 config FORCE_TASKS_RUDE_RCU << 98 bool "Force selection of Tasks Rude RC << 99 depends on RCU_EXPERT << 100 select TASKS_RUDE_RCU << 101 default n << 102 help << 103 This option force-enables a task-bas << 104 that uses only context switch (inclu << 105 user-mode execution as quiescent sta << 106 context switches on all online CPUs, << 107 so use with caution. Not for manual << 108 << 109 config TASKS_RUDE_RCU << 110 bool << 111 default n << 112 select IRQ_WORK << 113 << 114 config FORCE_TASKS_TRACE_RCU << 115 bool "Force selection of Tasks Trace R << 116 depends on RCU_EXPERT << 117 select TASKS_TRACE_RCU << 118 default n << 119 help 76 help 120 This option enables a task-based RCU 77 This option enables a task-based RCU implementation that uses 121 explicit rcu_read_lock_trace() read- !! 78 only voluntary context switch (not preemption!), idle, and 122 these readers to appear in the idle !! 79 user-mode execution as quiescent states. 123 CPU hotplug code paths. It can forc << 124 including idle ones, so use with cau << 125 selection in most cases. << 126 << 127 config TASKS_TRACE_RCU << 128 bool << 129 default n << 130 select IRQ_WORK << 131 80 132 config RCU_STALL_COMMON 81 config RCU_STALL_COMMON 133 def_bool TREE_RCU 82 def_bool TREE_RCU 134 help 83 help 135 This option enables RCU CPU stall co 84 This option enables RCU CPU stall code that is common between 136 the TINY and TREE variants of RCU. 85 the TINY and TREE variants of RCU. The purpose is to allow 137 the tiny variants to disable RCU CPU 86 the tiny variants to disable RCU CPU stall warnings, while 138 making these warnings mandatory for 87 making these warnings mandatory for the tree variants. 139 88 140 config RCU_NEED_SEGCBLIST 89 config RCU_NEED_SEGCBLIST 141 def_bool ( TREE_RCU || TREE_SRCU || TA !! 90 def_bool ( TREE_RCU || TREE_SRCU ) 142 91 143 config RCU_FANOUT 92 config RCU_FANOUT 144 int "Tree-based hierarchical RCU fanou 93 int "Tree-based hierarchical RCU fanout value" 145 range 2 64 if 64BIT 94 range 2 64 if 64BIT 146 range 2 32 if !64BIT 95 range 2 32 if !64BIT 147 depends on TREE_RCU && RCU_EXPERT 96 depends on TREE_RCU && RCU_EXPERT 148 default 64 if 64BIT 97 default 64 if 64BIT 149 default 32 if !64BIT 98 default 32 if !64BIT 150 help 99 help 151 This option controls the fanout of h 100 This option controls the fanout of hierarchical implementations 152 of RCU, allowing RCU to work efficie 101 of RCU, allowing RCU to work efficiently on machines with 153 large numbers of CPUs. This value m 102 large numbers of CPUs. This value must be at least the fourth 154 root of NR_CPUS, which allows NR_CPU 103 root of NR_CPUS, which allows NR_CPUS to be insanely large. 155 The default value of RCU_FANOUT shou 104 The default value of RCU_FANOUT should be used for production 156 systems, but if you are stress-testi 105 systems, but if you are stress-testing the RCU implementation 157 itself, small RCU_FANOUT values allo 106 itself, small RCU_FANOUT values allow you to test large-system 158 code paths on small(er) systems. 107 code paths on small(er) systems. 159 108 160 Select a specific number if testing 109 Select a specific number if testing RCU itself. 161 Take the default if unsure. 110 Take the default if unsure. 162 111 163 config RCU_FANOUT_LEAF 112 config RCU_FANOUT_LEAF 164 int "Tree-based hierarchical RCU leaf- 113 int "Tree-based hierarchical RCU leaf-level fanout value" 165 range 2 64 if 64BIT && !RCU_STRICT_GRA !! 114 range 2 64 if 64BIT 166 range 2 32 if !64BIT && !RCU_STRICT_GR !! 115 range 2 32 if !64BIT 167 range 2 3 if RCU_STRICT_GRACE_PERIOD << 168 depends on TREE_RCU && RCU_EXPERT 116 depends on TREE_RCU && RCU_EXPERT 169 default 16 if !RCU_STRICT_GRACE_PERIOD !! 117 default 16 170 default 2 if RCU_STRICT_GRACE_PERIOD << 171 help 118 help 172 This option controls the leaf-level 119 This option controls the leaf-level fanout of hierarchical 173 implementations of RCU, and allows t 120 implementations of RCU, and allows trading off cache misses 174 against lock contention. Systems th 121 against lock contention. Systems that synchronize their 175 scheduling-clock interrupts for ener 122 scheduling-clock interrupts for energy-efficiency reasons will 176 want the default because the smaller 123 want the default because the smaller leaf-level fanout keeps 177 lock contention levels acceptably lo 124 lock contention levels acceptably low. Very large systems 178 (hundreds or thousands of CPUs) will 125 (hundreds or thousands of CPUs) will instead want to set this 179 value to the maximum value possible 126 value to the maximum value possible in order to reduce the 180 number of cache misses incurred duri 127 number of cache misses incurred during RCU's grace-period 181 initialization. These systems tend 128 initialization. These systems tend to run CPU-bound, and thus 182 are not helped by synchronized inter 129 are not helped by synchronized interrupts, and thus tend to 183 skew them, which reduces lock conten 130 skew them, which reduces lock contention enough that large 184 leaf-level fanouts work well. That 131 leaf-level fanouts work well. That said, setting leaf-level 185 fanout to a large number will likely 132 fanout to a large number will likely cause problematic 186 lock contention on the leaf-level rc 133 lock contention on the leaf-level rcu_node structures unless 187 you boot with the skew_tick kernel p 134 you boot with the skew_tick kernel parameter. 188 135 189 Select a specific number if testing 136 Select a specific number if testing RCU itself. 190 137 191 Select the maximum permissible value 138 Select the maximum permissible value for large systems, but 192 please understand that you may also 139 please understand that you may also need to set the skew_tick 193 kernel boot parameter to avoid conte 140 kernel boot parameter to avoid contention on the rcu_node 194 structure's locks. 141 structure's locks. 195 142 196 Take the default if unsure. 143 Take the default if unsure. 197 144 >> 145 config RCU_FAST_NO_HZ >> 146 bool "Accelerate last non-dyntick-idle CPU's grace periods" >> 147 depends on NO_HZ_COMMON && SMP && RCU_EXPERT >> 148 default n >> 149 help >> 150 This option permits CPUs to enter dynticks-idle state even if >> 151 they have RCU callbacks queued, and prevents RCU from waking >> 152 these CPUs up more than roughly once every four jiffies (by >> 153 default, you can adjust this using the rcutree.rcu_idle_gp_delay >> 154 parameter), thus improving energy efficiency. On the other >> 155 hand, this option increases the duration of RCU grace periods, >> 156 for example, slowing down synchronize_rcu(). >> 157 >> 158 Say Y if energy efficiency is critically important, and you >> 159 don't care about increased grace-period durations. >> 160 >> 161 Say N if you are unsure. >> 162 198 config RCU_BOOST 163 config RCU_BOOST 199 bool "Enable RCU priority boosting" 164 bool "Enable RCU priority boosting" 200 depends on (RT_MUTEXES && PREEMPT_RCU !! 165 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT 201 default y if PREEMPT_RT !! 166 default n 202 help 167 help 203 This option boosts the priority of p 168 This option boosts the priority of preempted RCU readers that 204 block the current preemptible RCU gr 169 block the current preemptible RCU grace period for too long. 205 This option also prevents heavy load 170 This option also prevents heavy loads from blocking RCU 206 callback invocation. 171 callback invocation. 207 172 208 Say Y here if you are working with r 173 Say Y here if you are working with real-time apps or heavy loads 209 Say N here if you are unsure. 174 Say N here if you are unsure. 210 175 211 config RCU_BOOST_DELAY 176 config RCU_BOOST_DELAY 212 int "Milliseconds to delay boosting af 177 int "Milliseconds to delay boosting after RCU grace-period start" 213 range 0 3000 178 range 0 3000 214 depends on RCU_BOOST 179 depends on RCU_BOOST 215 default 500 180 default 500 216 help 181 help 217 This option specifies the time to wa 182 This option specifies the time to wait after the beginning of 218 a given grace period before priority 183 a given grace period before priority-boosting preempted RCU 219 readers blocking that grace period. 184 readers blocking that grace period. Note that any RCU reader 220 blocking an expedited RCU grace peri 185 blocking an expedited RCU grace period is boosted immediately. 221 186 222 Accept the default if unsure. 187 Accept the default if unsure. 223 188 224 config RCU_EXP_KTHREAD << 225 bool "Perform RCU expedited work in a << 226 depends on RCU_BOOST && RCU_EXPERT << 227 default !PREEMPT_RT && NR_CPUS <= 32 << 228 help << 229 Use this option to further reduce th << 230 grace periods at the expense of bein << 231 << 232 This option is disabled by default o << 233 disable expedited grace periods afte << 234 setting rcupdate.rcu_normal_after_bo << 235 << 236 Accept the default if unsure. << 237 << 238 config RCU_NOCB_CPU 189 config RCU_NOCB_CPU 239 bool "Offload RCU callback processing 190 bool "Offload RCU callback processing from boot-selected CPUs" 240 depends on TREE_RCU 191 depends on TREE_RCU 241 depends on RCU_EXPERT || NO_HZ_FULL 192 depends on RCU_EXPERT || NO_HZ_FULL 242 default n 193 default n 243 help 194 help 244 Use this option to reduce OS jitter 195 Use this option to reduce OS jitter for aggressive HPC or 245 real-time workloads. It can also be 196 real-time workloads. It can also be used to offload RCU 246 callback invocation to energy-effici 197 callback invocation to energy-efficient CPUs in battery-powered 247 asymmetric multiprocessors. The pri !! 198 asymmetric multiprocessors. 248 is that the overhead of call_rcu() i << 249 workloads will incur significant inc << 250 rates. << 251 199 252 This option offloads callback invoca 200 This option offloads callback invocation from the set of CPUs 253 specified at boot time by the rcu_no 201 specified at boot time by the rcu_nocbs parameter. For each 254 such CPU, a kthread ("rcuox/N") will 202 such CPU, a kthread ("rcuox/N") will be created to invoke 255 callbacks, where the "N" is the CPU 203 callbacks, where the "N" is the CPU being offloaded, and where 256 the "x" is "p" for RCU-preempt (PREE !! 204 the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched 257 RCU-sched (!PREEMPTION kernels). No !! 205 (!PREEMPTION kernels). Nothing prevents this kthread from running 258 from running on the specified CPUs, !! 206 on the specified CPUs, but (1) the kthreads may be preempted 259 preempted between each callback, and !! 207 between each callback, and (2) affinity or cgroups can be used 260 be used to force the kthreads to run !! 208 to force the kthreads to run on whatever set of CPUs is desired. 261 desired. << 262 << 263 Say Y here if you need reduced OS ji << 264 Say N here if you are unsure. << 265 << 266 config RCU_NOCB_CPU_DEFAULT_ALL << 267 bool "Offload RCU callback processing << 268 depends on RCU_NOCB_CPU << 269 default n << 270 help << 271 Use this option to offload callback << 272 by default, in the absence of the rc << 273 parameter. This also avoids the need << 274 to achieve the effect of offloading << 275 << 276 Say Y here if you want offload all C << 277 Say N here if you are unsure. << 278 << 279 config RCU_NOCB_CPU_CB_BOOST << 280 bool "Offload RCU callback from real-t << 281 depends on RCU_NOCB_CPU && RCU_BOOST << 282 default y if PREEMPT_RT << 283 help << 284 Use this option to invoke offloaded << 285 to avoid starvation by heavy SCHED_O << 286 Of course, running as SCHED_FIFO dur << 287 cause the rcuo[ps] kthreads to monop << 288 of milliseconds or more. Therefore, << 289 it is your responsibility to ensure << 290 tasks either run with higher priorit << 291 << 292 Say Y here if you want to set RT pri << 293 Say N here if you are building a !PR << 294 << 295 config TASKS_TRACE_RCU_READ_MB << 296 bool "Tasks Trace RCU readers use memo << 297 depends on RCU_EXPERT && TASKS_TRACE_R << 298 default PREEMPT_RT || NR_CPUS < 8 << 299 help << 300 Use this option to further reduce th << 301 to CPUs executing in userspace or id << 302 RCU grace periods. Given that a rea << 303 the rcupdate.rcu_task_ipi_delay kern << 304 eliminates such IPIs for many worklo << 305 of this Kconfig option is important << 306 real-time installations and for batt << 307 hence the default chosen above. << 308 << 309 Say Y here if you hate IPIs. << 310 Say N here if you hate read-side mem << 311 Take the default if you are unsure. << 312 << 313 config RCU_LAZY << 314 bool "RCU callback lazy invocation fun << 315 depends on RCU_NOCB_CPU << 316 default n << 317 help << 318 To save power, batch RCU callbacks a << 319 pressure, or callback list growing t << 320 << 321 Requires rcu_nocbs=all to be set. << 322 << 323 Use rcutree.enable_rcu_lazy=0 to tur << 324 << 325 config RCU_LAZY_DEFAULT_OFF << 326 bool "Turn RCU lazy invocation off by << 327 depends on RCU_LAZY << 328 default n << 329 help << 330 Allows building the kernel with CONF << 331 off. Boot time param rcutree.enable_ << 332 it back on. << 333 << 334 config RCU_DOUBLE_CHECK_CB_TIME << 335 bool "RCU callback-batch backup time c << 336 depends on RCU_EXPERT << 337 default n << 338 help << 339 Use this option to provide more prec << 340 rcutree.rcu_resched_ns module parame << 341 a single RCU callback might run for << 342 thus defeating the 32-callback batch << 343 cost of the fine-grained but expensi << 344 << 345 This option rounds rcutree.rcu_resch << 346 jiffy, and overrides the 32-callback << 347 is exceeded. << 348 209 349 Say Y here if you need tighter callb !! 210 Say Y here if you want to help to debug reduced OS jitter. 350 Say N here if you are unsure. 211 Say N here if you are unsure. 351 212 352 endmenu # "RCU Subsystem" 213 endmenu # "RCU Subsystem"

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Linux/kernel/rcu/Kconfig

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Differences between /kernel/rcu/Kconfig (Version linux-6.11.5) and /kernel/rcu/Kconfig (Version linux-5.6.19)

TOMOYO Linux Cross Reference Linux/kernel/rcu/Kconfig

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Differences between /kernel/rcu/Kconfig (Version linux-6.11.5) and /kernel/rcu/Kconfig (Version linux-5.6.19)

TOMOYO Linux Cross Reference
Linux/kernel/rcu/Kconfig