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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