1 # SPDX-License-Identifier: GPL-2.0-only 2 # 3 # RCU-related configuration options 4 # 5 6 menu "RCU Subsystem" 7 8 config TREE_RCU 9 bool 10 default y if SMP 11 # Dynticks-idle tracking 12 select CONTEXT_TRACKING_IDLE 13 help 14 This option selects the RCU implemen 15 designed for very large SMP system w 16 thousands of CPUs. It also scales d 17 smaller systems. 18 19 config PREEMPT_RCU 20 bool 21 default y if PREEMPTION 22 select TREE_RCU 23 help 24 This option selects the RCU implemen 25 designed for very large SMP systems 26 thousands of CPUs, but for which rea 27 is also required. It also scales do 28 smaller systems. 29 30 Select this option if you are unsure 31 32 config TINY_RCU 33 bool 34 default y if !PREEMPT_RCU && !SMP 35 help 36 This option selects the RCU implemen 37 designed for UP systems from which r 38 is not required. This option greatl 39 memory footprint of RCU. 40 41 config RCU_EXPERT 42 bool "Make expert-level adjustments to 43 default n 44 help 45 This option needs to be enabled if y 46 expert-level adjustments to RCU conf 47 no such adjustments can be made, whi 48 side-effect of preventing "make oldc 49 sorts of detailed questions about ho 50 obscure RCU options to be set up. 51 52 Say Y if you need to make expert-lev 53 54 Say N if you are unsure. 55 56 config TINY_SRCU 57 bool 58 default y if TINY_RCU 59 help 60 This option selects the single-CPU n 61 62 config TREE_SRCU 63 bool 64 default y if !TINY_RCU 65 help 66 This option selects the full-fledged 67 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 93 bool 94 default NEED_TASKS_RCU && (PREEMPTION 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 120 This option enables a task-based RCU 121 explicit rcu_read_lock_trace() read- 122 these readers to appear in the idle 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 131 132 config RCU_STALL_COMMON 133 def_bool TREE_RCU 134 help 135 This option enables RCU CPU stall co 136 the TINY and TREE variants of RCU. 137 the tiny variants to disable RCU CPU 138 making these warnings mandatory for 139 140 config RCU_NEED_SEGCBLIST 141 def_bool ( TREE_RCU || TREE_SRCU || TA 142 143 config RCU_FANOUT 144 int "Tree-based hierarchical RCU fanou 145 range 2 64 if 64BIT 146 range 2 32 if !64BIT 147 depends on TREE_RCU && RCU_EXPERT 148 default 64 if 64BIT 149 default 32 if !64BIT 150 help 151 This option controls the fanout of h 152 of RCU, allowing RCU to work efficie 153 large numbers of CPUs. This value m 154 root of NR_CPUS, which allows NR_CPU 155 The default value of RCU_FANOUT shou 156 systems, but if you are stress-testi 157 itself, small RCU_FANOUT values allo 158 code paths on small(er) systems. 159 160 Select a specific number if testing 161 Take the default if unsure. 162 163 config RCU_FANOUT_LEAF 164 int "Tree-based hierarchical RCU leaf- 165 range 2 64 if 64BIT && !RCU_STRICT_GRA 166 range 2 32 if !64BIT && !RCU_STRICT_GR 167 range 2 3 if RCU_STRICT_GRACE_PERIOD 168 depends on TREE_RCU && RCU_EXPERT 169 default 16 if !RCU_STRICT_GRACE_PERIOD 170 default 2 if RCU_STRICT_GRACE_PERIOD 171 help 172 This option controls the leaf-level 173 implementations of RCU, and allows t 174 against lock contention. Systems th 175 scheduling-clock interrupts for ener 176 want the default because the smaller 177 lock contention levels acceptably lo 178 (hundreds or thousands of CPUs) will 179 value to the maximum value possible 180 number of cache misses incurred duri 181 initialization. These systems tend 182 are not helped by synchronized inter 183 skew them, which reduces lock conten 184 leaf-level fanouts work well. That 185 fanout to a large number will likely 186 lock contention on the leaf-level rc 187 you boot with the skew_tick kernel p 188 189 Select a specific number if testing 190 191 Select the maximum permissible value 192 please understand that you may also 193 kernel boot parameter to avoid conte 194 structure's locks. 195 196 Take the default if unsure. 197 198 config RCU_BOOST 199 bool "Enable RCU priority boosting" 200 depends on (RT_MUTEXES && PREEMPT_RCU 201 default y if PREEMPT_RT 202 help 203 This option boosts the priority of p 204 block the current preemptible RCU gr 205 This option also prevents heavy load 206 callback invocation. 207 208 Say Y here if you are working with r 209 Say N here if you are unsure. 210 211 config RCU_BOOST_DELAY 212 int "Milliseconds to delay boosting af 213 range 0 3000 214 depends on RCU_BOOST 215 default 500 216 help 217 This option specifies the time to wa 218 a given grace period before priority 219 readers blocking that grace period. 220 blocking an expedited RCU grace peri 221 222 Accept the default if unsure. 223 224 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 239 bool "Offload RCU callback processing 240 depends on TREE_RCU 241 depends on RCU_EXPERT || NO_HZ_FULL 242 default n 243 help 244 Use this option to reduce OS jitter 245 real-time workloads. It can also be 246 callback invocation to energy-effici 247 asymmetric multiprocessors. The pri 248 is that the overhead of call_rcu() i 249 workloads will incur significant inc 250 rates. 251 252 This option offloads callback invoca 253 specified at boot time by the rcu_no 254 such CPU, a kthread ("rcuox/N") will 255 callbacks, where the "N" is the CPU 256 the "x" is "p" for RCU-preempt (PREE 257 RCU-sched (!PREEMPTION kernels). No 258 from running on the specified CPUs, 259 preempted between each callback, and 260 be used to force the kthreads to run 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. 348 349 Say Y here if you need tighter callb 350 Say N here if you are unsure. 351 352 endmenu # "RCU Subsystem"
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