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ec8f24b7 1# SPDX-License-Identifier: GPL-2.0-only
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2config DEFCONFIG_LIST
3 string
b2670eac 4 depends on !UML
face4374 5 option defconfig_list
47f38ae0 6 default "/lib/modules/$(shell,uname -r)/.config"
face4374 7 default "/etc/kernel-config"
47f38ae0 8 default "/boot/config-$(shell,uname -r)"
2a86f661 9 default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)"
face4374 10
8b59cd81
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11config CC_VERSION_TEXT
12 string
13 default "$(CC_VERSION_TEXT)"
14 help
15 This is used in unclear ways:
16
17 - Re-run Kconfig when the compiler is updated
18 The 'default' property references the environment variable,
19 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
20 When the compiler is updated, Kconfig will be invoked.
21
22 - Ensure full rebuild when the compier is updated
23 include/linux/kconfig.h contains this option in the comment line so
24 fixdep adds include/config/cc/version/text.h into the auto-generated
25 dependency. When the compiler is updated, syncconfig will touch it
26 and then every file will be rebuilt.
27
a4353898 28config CC_IS_GCC
e33ae3ed 29 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q gcc)
a4353898
MY
30
31config GCC_VERSION
32 int
fa7295ab 33 default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
a4353898
MY
34 default 0
35
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36config LD_VERSION
37 int
38 default $(shell,$(LD) --version | $(srctree)/scripts/ld-version.sh)
39
469cb737 40config CC_IS_CLANG
e33ae3ed 41 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q clang)
469cb737 42
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43config LD_IS_LLD
44 def_bool $(success,$(LD) -v | head -n 1 | grep -q LLD)
45
469cb737
MY
46config CLANG_VERSION
47 int
48 default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
49
1a927fd3 50config CC_CAN_LINK
9371f86e
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51 bool
52 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(m64-flag)) if 64BIT
53 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(m32-flag))
b1183b6d
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54
55config CC_CAN_LINK_STATIC
56 bool
57 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m64-flag)) if 64BIT
58 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m32-flag))
1a927fd3 59
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60config CC_HAS_ASM_GOTO
61 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
62
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63config CC_HAS_ASM_GOTO_OUTPUT
64 depends on CC_HAS_ASM_GOTO
65 def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
66
5cf896fb 67config TOOLS_SUPPORT_RELR
2d122942 68 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
5cf896fb 69
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70config CC_HAS_ASM_INLINE
71 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
72
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73config CONSTRUCTORS
74 bool
87c9366e 75 depends on !UML
b99b87f7 76
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77config IRQ_WORK
78 bool
e360adbe 79
10916706 80config BUILDTIME_TABLE_SORT
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81 bool
82
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83config THREAD_INFO_IN_TASK
84 bool
85 help
86 Select this to move thread_info off the stack into task_struct. To
87 make this work, an arch will need to remove all thread_info fields
88 except flags and fix any runtime bugs.
89
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90 One subtle change that will be needed is to use try_get_task_stack()
91 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
92
ff0cfc66 93menu "General setup"
1da177e4 94
1da177e4
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95config BROKEN
96 bool
1da177e4
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97
98config BROKEN_ON_SMP
99 bool
100 depends on BROKEN || !SMP
101 default y
102
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103config INIT_ENV_ARG_LIMIT
104 int
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105 default 32 if !UML
106 default 128 if UML
1da177e4 107 help
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108 Maximum of each of the number of arguments and environment
109 variables passed to init from the kernel command line.
1da177e4 110
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111config COMPILE_TEST
112 bool "Compile also drivers which will not load"
bc083a64 113 depends on !UML
4bb16672
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114 default n
115 help
116 Some drivers can be compiled on a different platform than they are
117 intended to be run on. Despite they cannot be loaded there (or even
118 when they load they cannot be used due to missing HW support),
119 developers still, opposing to distributors, might want to build such
120 drivers to compile-test them.
121
122 If you are a developer and want to build everything available, say Y
123 here. If you are a user/distributor, say N here to exclude useless
124 drivers to be distributed.
125
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126config UAPI_HEADER_TEST
127 bool "Compile test UAPI headers"
fcbb8461 128 depends on HEADERS_INSTALL && CC_CAN_LINK
d6fc9fcb
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129 help
130 Compile test headers exported to user-space to ensure they are
131 self-contained, i.e. compilable as standalone units.
132
133 If you are a developer or tester and want to ensure the exported
134 headers are self-contained, say Y here. Otherwise, choose N.
135
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136config LOCALVERSION
137 string "Local version - append to kernel release"
138 help
139 Append an extra string to the end of your kernel version.
140 This will show up when you type uname, for example.
141 The string you set here will be appended after the contents of
142 any files with a filename matching localversion* in your
143 object and source tree, in that order. Your total string can
144 be a maximum of 64 characters.
145
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146config LOCALVERSION_AUTO
147 bool "Automatically append version information to the version string"
148 default y
ac3339ba 149 depends on !COMPILE_TEST
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150 help
151 This will try to automatically determine if the current tree is a
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152 release tree by looking for git tags that belong to the current
153 top of tree revision.
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154
155 A string of the format -gxxxxxxxx will be added to the localversion
6e5a5420 156 if a git-based tree is found. The string generated by this will be
aaebf433 157 appended after any matching localversion* files, and after the value
6e5a5420 158 set in CONFIG_LOCALVERSION.
aaebf433 159
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160 (The actual string used here is the first eight characters produced
161 by running the command:
162
163 $ git rev-parse --verify HEAD
164
165 which is done within the script "scripts/setlocalversion".)
aaebf433 166
9afb719e 167config BUILD_SALT
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168 string "Build ID Salt"
169 default ""
170 help
171 The build ID is used to link binaries and their debug info. Setting
172 this option will use the value in the calculation of the build id.
173 This is mostly useful for distributions which want to ensure the
174 build is unique between builds. It's safe to leave the default.
9afb719e 175
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176config HAVE_KERNEL_GZIP
177 bool
178
179config HAVE_KERNEL_BZIP2
180 bool
181
182config HAVE_KERNEL_LZMA
183 bool
184
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185config HAVE_KERNEL_XZ
186 bool
187
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188config HAVE_KERNEL_LZO
189 bool
190
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191config HAVE_KERNEL_LZ4
192 bool
193
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194config HAVE_KERNEL_UNCOMPRESSED
195 bool
196
30d65dbf 197choice
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198 prompt "Kernel compression mode"
199 default KERNEL_GZIP
f16466af 200 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
2e9f3bdd 201 help
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202 The linux kernel is a kind of self-extracting executable.
203 Several compression algorithms are available, which differ
204 in efficiency, compression and decompression speed.
205 Compression speed is only relevant when building a kernel.
206 Decompression speed is relevant at each boot.
207
208 If you have any problems with bzip2 or lzma compressed
209 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
210 version of this functionality (bzip2 only), for 2.4, was
211 supplied by Christian Ludwig)
212
213 High compression options are mostly useful for users, who
214 are low on disk space (embedded systems), but for whom ram
215 size matters less.
216
217 If in doubt, select 'gzip'
218
219config KERNEL_GZIP
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220 bool "Gzip"
221 depends on HAVE_KERNEL_GZIP
222 help
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223 The old and tried gzip compression. It provides a good balance
224 between compression ratio and decompression speed.
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225
226config KERNEL_BZIP2
227 bool "Bzip2"
2e9f3bdd 228 depends on HAVE_KERNEL_BZIP2
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229 help
230 Its compression ratio and speed is intermediate.
0a4dd35c 231 Decompression speed is slowest among the choices. The kernel
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232 size is about 10% smaller with bzip2, in comparison to gzip.
233 Bzip2 uses a large amount of memory. For modern kernels you
234 will need at least 8MB RAM or more for booting.
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235
236config KERNEL_LZMA
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237 bool "LZMA"
238 depends on HAVE_KERNEL_LZMA
239 help
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240 This compression algorithm's ratio is best. Decompression speed
241 is between gzip and bzip2. Compression is slowest.
242 The kernel size is about 33% smaller with LZMA in comparison to gzip.
30d65dbf 243
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244config KERNEL_XZ
245 bool "XZ"
246 depends on HAVE_KERNEL_XZ
247 help
248 XZ uses the LZMA2 algorithm and instruction set specific
249 BCJ filters which can improve compression ratio of executable
250 code. The size of the kernel is about 30% smaller with XZ in
251 comparison to gzip. On architectures for which there is a BCJ
252 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
253 will create a few percent smaller kernel than plain LZMA.
254
255 The speed is about the same as with LZMA: The decompression
256 speed of XZ is better than that of bzip2 but worse than gzip
257 and LZO. Compression is slow.
258
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259config KERNEL_LZO
260 bool "LZO"
261 depends on HAVE_KERNEL_LZO
262 help
0a4dd35c 263 Its compression ratio is the poorest among the choices. The kernel
681b3049 264 size is about 10% bigger than gzip; however its speed
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265 (both compression and decompression) is the fastest.
266
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267config KERNEL_LZ4
268 bool "LZ4"
269 depends on HAVE_KERNEL_LZ4
270 help
271 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
272 A preliminary version of LZ4 de/compression tool is available at
273 <https://code.google.com/p/lz4/>.
274
275 Its compression ratio is worse than LZO. The size of the kernel
276 is about 8% bigger than LZO. But the decompression speed is
277 faster than LZO.
278
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279config KERNEL_UNCOMPRESSED
280 bool "None"
281 depends on HAVE_KERNEL_UNCOMPRESSED
282 help
283 Produce uncompressed kernel image. This option is usually not what
284 you want. It is useful for debugging the kernel in slow simulation
285 environments, where decompressing and moving the kernel is awfully
286 slow. This option allows early boot code to skip the decompressor
287 and jump right at uncompressed kernel image.
288
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289endchoice
290
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291config DEFAULT_INIT
292 string "Default init path"
293 default ""
294 help
295 This option determines the default init for the system if no init=
296 option is passed on the kernel command line. If the requested path is
297 not present, we will still then move on to attempting further
298 locations (e.g. /sbin/init, etc). If this is empty, we will just use
299 the fallback list when init= is not passed.
300
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301config DEFAULT_HOSTNAME
302 string "Default hostname"
303 default "(none)"
304 help
305 This option determines the default system hostname before userspace
306 calls sethostname(2). The kernel traditionally uses "(none)" here,
307 but you may wish to use a different default here to make a minimal
308 system more usable with less configuration.
309
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310#
311# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
312# add proper SWAP support to them, in which case this can be remove.
313#
314config ARCH_NO_SWAP
315 bool
316
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317config SWAP
318 bool "Support for paging of anonymous memory (swap)"
17c46a6a 319 depends on MMU && BLOCK && !ARCH_NO_SWAP
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320 default y
321 help
322 This option allows you to choose whether you want to have support
92c3504e 323 for so called swap devices or swap files in your kernel that are
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324 used to provide more virtual memory than the actual RAM present
325 in your computer. If unsure say Y.
326
327config SYSVIPC
328 bool "System V IPC"
1da177e4
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329 ---help---
330 Inter Process Communication is a suite of library functions and
331 system calls which let processes (running programs) synchronize and
332 exchange information. It is generally considered to be a good thing,
333 and some programs won't run unless you say Y here. In particular, if
334 you want to run the DOS emulator dosemu under Linux (read the
335 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
336 you'll need to say Y here.
337
338 You can find documentation about IPC with "info ipc" and also in
339 section 6.4 of the Linux Programmer's Guide, available from
340 <http://www.tldp.org/guides.html>.
341
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342config SYSVIPC_SYSCTL
343 bool
344 depends on SYSVIPC
345 depends on SYSCTL
346 default y
347
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348config POSIX_MQUEUE
349 bool "POSIX Message Queues"
19c92399 350 depends on NET
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351 ---help---
352 POSIX variant of message queues is a part of IPC. In POSIX message
353 queues every message has a priority which decides about succession
354 of receiving it by a process. If you want to compile and run
355 programs written e.g. for Solaris with use of its POSIX message
b0e37650 356 queues (functions mq_*) say Y here.
1da177e4
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357
358 POSIX message queues are visible as a filesystem called 'mqueue'
359 and can be mounted somewhere if you want to do filesystem
360 operations on message queues.
361
362 If unsure, say Y.
363
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364config POSIX_MQUEUE_SYSCTL
365 bool
366 depends on POSIX_MQUEUE
367 depends on SYSCTL
368 default y
369
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370config CROSS_MEMORY_ATTACH
371 bool "Enable process_vm_readv/writev syscalls"
372 depends on MMU
373 default y
374 help
375 Enabling this option adds the system calls process_vm_readv and
376 process_vm_writev which allow a process with the correct privileges
a2a368d9 377 to directly read from or write to another process' address space.
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378 See the man page for more details.
379
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380config USELIB
381 bool "uselib syscall"
b2113a41 382 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
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383 help
384 This option enables the uselib syscall, a system call used in the
385 dynamic linker from libc5 and earlier. glibc does not use this
386 system call. If you intend to run programs built on libc5 or
387 earlier, you may need to enable this syscall. Current systems
388 running glibc can safely disable this.
389
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390config AUDIT
391 bool "Auditing support"
392 depends on NET
393 help
394 Enable auditing infrastructure that can be used with another
395 kernel subsystem, such as SELinux (which requires this for
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396 logging of avc messages output). System call auditing is included
397 on architectures which support it.
391dc69c 398
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399config HAVE_ARCH_AUDITSYSCALL
400 bool
401
391dc69c 402config AUDITSYSCALL
cb74ed27 403 def_bool y
7a017721 404 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
391dc69c
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405 select FSNOTIFY
406
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407source "kernel/irq/Kconfig"
408source "kernel/time/Kconfig"
87a4c375 409source "kernel/Kconfig.preempt"
391dc69c
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410
411menu "CPU/Task time and stats accounting"
412
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413config VIRT_CPU_ACCOUNTING
414 bool
415
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416choice
417 prompt "Cputime accounting"
418 default TICK_CPU_ACCOUNTING if !PPC64
02fc8d37 419 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
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420
421# Kind of a stub config for the pure tick based cputime accounting
422config TICK_CPU_ACCOUNTING
423 bool "Simple tick based cputime accounting"
c58b0df1 424 depends on !S390 && !NO_HZ_FULL
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425 help
426 This is the basic tick based cputime accounting that maintains
427 statistics about user, system and idle time spent on per jiffies
428 granularity.
429
430 If unsure, say Y.
431
abf917cd 432config VIRT_CPU_ACCOUNTING_NATIVE
b952741c 433 bool "Deterministic task and CPU time accounting"
c58b0df1 434 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
abf917cd 435 select VIRT_CPU_ACCOUNTING
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436 help
437 Select this option to enable more accurate task and CPU time
438 accounting. This is done by reading a CPU counter on each
439 kernel entry and exit and on transitions within the kernel
440 between system, softirq and hardirq state, so there is a
441 small performance impact. In the case of s390 or IBM POWER > 5,
442 this also enables accounting of stolen time on logically-partitioned
443 systems.
444
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445config VIRT_CPU_ACCOUNTING_GEN
446 bool "Full dynticks CPU time accounting"
ff3fb254 447 depends on HAVE_CONTEXT_TRACKING
554b0004 448 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
041a1574 449 depends on GENERIC_CLOCKEVENTS
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450 select VIRT_CPU_ACCOUNTING
451 select CONTEXT_TRACKING
452 help
453 Select this option to enable task and CPU time accounting on full
454 dynticks systems. This accounting is implemented by watching every
455 kernel-user boundaries using the context tracking subsystem.
456 The accounting is thus performed at the expense of some significant
457 overhead.
458
459 For now this is only useful if you are working on the full
460 dynticks subsystem development.
461
462 If unsure, say N.
463
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464endchoice
465
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466config IRQ_TIME_ACCOUNTING
467 bool "Fine granularity task level IRQ time accounting"
b58c3584 468 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
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469 help
470 Select this option to enable fine granularity task irq time
471 accounting. This is done by reading a timestamp on each
472 transitions between softirq and hardirq state, so there can be a
473 small performance impact.
474
475 If in doubt, say N here.
476
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477config HAVE_SCHED_AVG_IRQ
478 def_bool y
479 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
480 depends on SMP
481
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482config SCHED_THERMAL_PRESSURE
483 bool "Enable periodic averaging of thermal pressure"
484 depends on SMP
485
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486config BSD_PROCESS_ACCT
487 bool "BSD Process Accounting"
2813893f 488 depends on MULTIUSER
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489 help
490 If you say Y here, a user level program will be able to instruct the
491 kernel (via a special system call) to write process accounting
492 information to a file: whenever a process exits, information about
493 that process will be appended to the file by the kernel. The
494 information includes things such as creation time, owning user,
495 command name, memory usage, controlling terminal etc. (the complete
496 list is in the struct acct in <file:include/linux/acct.h>). It is
497 up to the user level program to do useful things with this
498 information. This is generally a good idea, so say Y.
499
500config BSD_PROCESS_ACCT_V3
501 bool "BSD Process Accounting version 3 file format"
502 depends on BSD_PROCESS_ACCT
503 default n
504 help
505 If you say Y here, the process accounting information is written
506 in a new file format that also logs the process IDs of each
3903bf94 507 process and its parent. Note that this file format is incompatible
1da177e4
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508 with previous v0/v1/v2 file formats, so you will need updated tools
509 for processing it. A preliminary version of these tools is available
37a4c940 510 at <http://www.gnu.org/software/acct/>.
1da177e4 511
c757249a 512config TASKSTATS
19c92399 513 bool "Export task/process statistics through netlink"
c757249a 514 depends on NET
2813893f 515 depends on MULTIUSER
c757249a
SN
516 default n
517 help
518 Export selected statistics for tasks/processes through the
519 generic netlink interface. Unlike BSD process accounting, the
520 statistics are available during the lifetime of tasks/processes as
521 responses to commands. Like BSD accounting, they are sent to user
522 space on task exit.
523
524 Say N if unsure.
525
ca74e92b 526config TASK_DELAY_ACCT
19c92399 527 bool "Enable per-task delay accounting"
6f44993f 528 depends on TASKSTATS
f6db8347 529 select SCHED_INFO
ca74e92b
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530 help
531 Collect information on time spent by a task waiting for system
532 resources like cpu, synchronous block I/O completion and swapping
533 in pages. Such statistics can help in setting a task's priorities
534 relative to other tasks for cpu, io, rss limits etc.
535
536 Say N if unsure.
537
18f705f4 538config TASK_XACCT
19c92399 539 bool "Enable extended accounting over taskstats"
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540 depends on TASKSTATS
541 help
542 Collect extended task accounting data and send the data
543 to userland for processing over the taskstats interface.
544
545 Say N if unsure.
546
547config TASK_IO_ACCOUNTING
19c92399 548 bool "Enable per-task storage I/O accounting"
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549 depends on TASK_XACCT
550 help
551 Collect information on the number of bytes of storage I/O which this
552 task has caused.
553
554 Say N if unsure.
555
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556config PSI
557 bool "Pressure stall information tracking"
558 help
559 Collect metrics that indicate how overcommitted the CPU, memory,
560 and IO capacity are in the system.
561
562 If you say Y here, the kernel will create /proc/pressure/ with the
563 pressure statistics files cpu, memory, and io. These will indicate
564 the share of walltime in which some or all tasks in the system are
565 delayed due to contention of the respective resource.
566
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567 In kernels with cgroup support, cgroups (cgroup2 only) will
568 have cpu.pressure, memory.pressure, and io.pressure files,
569 which aggregate pressure stalls for the grouped tasks only.
570
c3123552 571 For more details see Documentation/accounting/psi.rst.
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572
573 Say N if unsure.
574
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575config PSI_DEFAULT_DISABLED
576 bool "Require boot parameter to enable pressure stall information tracking"
577 default n
578 depends on PSI
579 help
580 If set, pressure stall information tracking will be disabled
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581 per default but can be enabled through passing psi=1 on the
582 kernel commandline during boot.
e0c27447 583
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584 This feature adds some code to the task wakeup and sleep
585 paths of the scheduler. The overhead is too low to affect
586 common scheduling-intense workloads in practice (such as
587 webservers, memcache), but it does show up in artificial
588 scheduler stress tests, such as hackbench.
589
590 If you are paranoid and not sure what the kernel will be
591 used for, say Y.
592
593 Say N if unsure.
594
391dc69c 595endmenu # "CPU/Task time and stats accounting"
d9817ebe 596
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597config CPU_ISOLATION
598 bool "CPU isolation"
414a2dc1 599 depends on SMP || COMPILE_TEST
2c43838c 600 default y
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601 help
602 Make sure that CPUs running critical tasks are not disturbed by
603 any source of "noise" such as unbound workqueues, timers, kthreads...
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604 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
605 the "isolcpus=" boot parameter.
606
607 Say Y if unsure.
5c4991e2 608
0af92d46 609source "kernel/rcu/Kconfig"
c903ff83 610
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611config BUILD_BIN2C
612 bool
613 default n
614
1da177e4 615config IKCONFIG
f2443ab6 616 tristate "Kernel .config support"
1da177e4
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617 ---help---
618 This option enables the complete Linux kernel ".config" file
619 contents to be saved in the kernel. It provides documentation
620 of which kernel options are used in a running kernel or in an
621 on-disk kernel. This information can be extracted from the kernel
622 image file with the script scripts/extract-ikconfig and used as
623 input to rebuild the current kernel or to build another kernel.
624 It can also be extracted from a running kernel by reading
625 /proc/config.gz if enabled (below).
626
627config IKCONFIG_PROC
628 bool "Enable access to .config through /proc/config.gz"
629 depends on IKCONFIG && PROC_FS
630 ---help---
631 This option enables access to the kernel configuration file
632 through /proc/config.gz.
633
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634config IKHEADERS
635 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
636 depends on SYSFS
637 help
638 This option enables access to the in-kernel headers that are generated during
639 the build process. These can be used to build eBPF tracing programs,
640 or similar programs. If you build the headers as a module, a module called
641 kheaders.ko is built which can be loaded on-demand to get access to headers.
43d8ce9d 642
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643config LOG_BUF_SHIFT
644 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
fb39f98d 645 range 12 25
f17a32e9 646 default 17
361e9dfb 647 depends on PRINTK
794543a2 648 help
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649 Select the minimal kernel log buffer size as a power of 2.
650 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
651 parameter, see below. Any higher size also might be forced
652 by "log_buf_len" boot parameter.
653
f17a32e9 654 Examples:
23b2899f 655 17 => 128 KB
f17a32e9 656 16 => 64 KB
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657 15 => 32 KB
658 14 => 16 KB
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659 13 => 8 KB
660 12 => 4 KB
661
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662config LOG_CPU_MAX_BUF_SHIFT
663 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
2240a31d 664 depends on SMP
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665 range 0 21
666 default 12 if !BASE_SMALL
667 default 0 if BASE_SMALL
361e9dfb 668 depends on PRINTK
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669 help
670 This option allows to increase the default ring buffer size
671 according to the number of CPUs. The value defines the contribution
672 of each CPU as a power of 2. The used space is typically only few
673 lines however it might be much more when problems are reported,
674 e.g. backtraces.
675
676 The increased size means that a new buffer has to be allocated and
677 the original static one is unused. It makes sense only on systems
678 with more CPUs. Therefore this value is used only when the sum of
679 contributions is greater than the half of the default kernel ring
680 buffer as defined by LOG_BUF_SHIFT. The default values are set
681 so that more than 64 CPUs are needed to trigger the allocation.
682
683 Also this option is ignored when "log_buf_len" kernel parameter is
684 used as it forces an exact (power of two) size of the ring buffer.
685
686 The number of possible CPUs is used for this computation ignoring
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687 hotplugging making the computation optimal for the worst case
688 scenario while allowing a simple algorithm to be used from bootup.
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689
690 Examples shift values and their meaning:
691 17 => 128 KB for each CPU
692 16 => 64 KB for each CPU
693 15 => 32 KB for each CPU
694 14 => 16 KB for each CPU
695 13 => 8 KB for each CPU
696 12 => 4 KB for each CPU
697
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698config PRINTK_SAFE_LOG_BUF_SHIFT
699 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
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700 range 10 21
701 default 13
f92bac3b 702 depends on PRINTK
427934b8 703 help
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704 Select the size of an alternate printk per-CPU buffer where messages
705 printed from usafe contexts are temporary stored. One example would
706 be NMI messages, another one - printk recursion. The messages are
707 copied to the main log buffer in a safe context to avoid a deadlock.
708 The value defines the size as a power of 2.
427934b8 709
f92bac3b 710 Those messages are rare and limited. The largest one is when
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711 a backtrace is printed. It usually fits into 4KB. Select
712 8KB if you want to be on the safe side.
713
714 Examples:
715 17 => 128 KB for each CPU
716 16 => 64 KB for each CPU
717 15 => 32 KB for each CPU
718 14 => 16 KB for each CPU
719 13 => 8 KB for each CPU
720 12 => 4 KB for each CPU
721
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722#
723# Architectures with an unreliable sched_clock() should select this:
724#
725config HAVE_UNSTABLE_SCHED_CLOCK
726 bool
727
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728config GENERIC_SCHED_CLOCK
729 bool
730
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731menu "Scheduler features"
732
733config UCLAMP_TASK
734 bool "Enable utilization clamping for RT/FAIR tasks"
735 depends on CPU_FREQ_GOV_SCHEDUTIL
736 help
737 This feature enables the scheduler to track the clamped utilization
738 of each CPU based on RUNNABLE tasks scheduled on that CPU.
739
740 With this option, the user can specify the min and max CPU
741 utilization allowed for RUNNABLE tasks. The max utilization defines
742 the maximum frequency a task should use while the min utilization
743 defines the minimum frequency it should use.
744
745 Both min and max utilization clamp values are hints to the scheduler,
746 aiming at improving its frequency selection policy, but they do not
747 enforce or grant any specific bandwidth for tasks.
748
749 If in doubt, say N.
750
751config UCLAMP_BUCKETS_COUNT
752 int "Number of supported utilization clamp buckets"
753 range 5 20
754 default 5
755 depends on UCLAMP_TASK
756 help
757 Defines the number of clamp buckets to use. The range of each bucket
758 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
759 number of clamp buckets the finer their granularity and the higher
760 the precision of clamping aggregation and tracking at run-time.
761
762 For example, with the minimum configuration value we will have 5
763 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
764 be refcounted in the [20..39]% bucket and will set the bucket clamp
765 effective value to 25%.
766 If a second 30% boosted task should be co-scheduled on the same CPU,
767 that task will be refcounted in the same bucket of the first task and
768 it will boost the bucket clamp effective value to 30%.
769 The clamp effective value of a bucket is reset to its nominal value
770 (20% in the example above) when there are no more tasks refcounted in
771 that bucket.
772
773 An additional boost/capping margin can be added to some tasks. In the
774 example above the 25% task will be boosted to 30% until it exits the
775 CPU. If that should be considered not acceptable on certain systems,
776 it's always possible to reduce the margin by increasing the number of
777 clamp buckets to trade off used memory for run-time tracking
778 precision.
779
780 If in doubt, use the default value.
781
782endmenu
783
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784#
785# For architectures that want to enable the support for NUMA-affine scheduler
786# balancing logic:
787#
788config ARCH_SUPPORTS_NUMA_BALANCING
789 bool
790
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791#
792# For architectures that prefer to flush all TLBs after a number of pages
793# are unmapped instead of sending one IPI per page to flush. The architecture
794# must provide guarantees on what happens if a clean TLB cache entry is
795# written after the unmap. Details are in mm/rmap.c near the check for
796# should_defer_flush. The architecture should also consider if the full flush
797# and the refill costs are offset by the savings of sending fewer IPIs.
798config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
799 bool
800
c12d3362 801config CC_HAS_INT128
3a7c7331 802 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
c12d3362 803
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804#
805# For architectures that know their GCC __int128 support is sound
806#
807config ARCH_SUPPORTS_INT128
808 bool
809
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810# For architectures that (ab)use NUMA to represent different memory regions
811# all cpu-local but of different latencies, such as SuperH.
812#
813config ARCH_WANT_NUMA_VARIABLE_LOCALITY
814 bool
815
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816config NUMA_BALANCING
817 bool "Memory placement aware NUMA scheduler"
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AA
818 depends on ARCH_SUPPORTS_NUMA_BALANCING
819 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
820 depends on SMP && NUMA && MIGRATION
821 help
822 This option adds support for automatic NUMA aware memory/task placement.
823 The mechanism is quite primitive and is based on migrating memory when
6d56a410 824 it has references to the node the task is running on.
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AA
825
826 This system will be inactive on UMA systems.
827
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828config NUMA_BALANCING_DEFAULT_ENABLED
829 bool "Automatically enable NUMA aware memory/task placement"
830 default y
831 depends on NUMA_BALANCING
832 help
833 If set, automatic NUMA balancing will be enabled if running on a NUMA
834 machine.
835
23964d2d 836menuconfig CGROUPS
6341e62b 837 bool "Control Group support"
2bd59d48 838 select KERNFS
5cdc38f9 839 help
23964d2d 840 This option adds support for grouping sets of processes together, for
5cdc38f9
KH
841 use with process control subsystems such as Cpusets, CFS, memory
842 controls or device isolation.
843 See
d6a3b247 844 - Documentation/scheduler/sched-design-CFS.rst (CFS)
da82c92f 845 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
45ce80fb 846 and resource control)
5cdc38f9
KH
847
848 Say N if unsure.
849
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850if CGROUPS
851
3e32cb2e 852config PAGE_COUNTER
e8cf4e9c 853 bool
3e32cb2e 854
c255a458 855config MEMCG
a0166ec4 856 bool "Memory controller"
3e32cb2e 857 select PAGE_COUNTER
79bd9814 858 select EVENTFD
00f0b825 859 help
a0166ec4 860 Provides control over the memory footprint of tasks in a cgroup.
00f0b825 861
c255a458 862config MEMCG_SWAP
2d1c4980 863 bool
c255a458 864 depends on MEMCG && SWAP
a42c390c 865 default y
c077719b 866
84c07d11
KT
867config MEMCG_KMEM
868 bool
869 depends on MEMCG && !SLOB
870 default y
871
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872config BLK_CGROUP
873 bool "IO controller"
874 depends on BLOCK
2bc64a20 875 default n
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876 ---help---
877 Generic block IO controller cgroup interface. This is the common
878 cgroup interface which should be used by various IO controlling
879 policies.
2bc64a20 880
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881 Currently, CFQ IO scheduler uses it to recognize task groups and
882 control disk bandwidth allocation (proportional time slice allocation)
883 to such task groups. It is also used by bio throttling logic in
884 block layer to implement upper limit in IO rates on a device.
e5d1367f 885
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886 This option only enables generic Block IO controller infrastructure.
887 One needs to also enable actual IO controlling logic/policy. For
888 enabling proportional weight division of disk bandwidth in CFQ, set
7baf2199 889 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
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JW
890 CONFIG_BLK_DEV_THROTTLING=y.
891
da82c92f 892 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
6bf024e6 893
6bf024e6
JW
894config CGROUP_WRITEBACK
895 bool
896 depends on MEMCG && BLK_CGROUP
897 default y
e5d1367f 898
7c941438 899menuconfig CGROUP_SCHED
a0166ec4 900 bool "CPU controller"
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DG
901 default n
902 help
903 This feature lets CPU scheduler recognize task groups and control CPU
904 bandwidth allocation to such task groups. It uses cgroups to group
905 tasks.
906
907if CGROUP_SCHED
908config FAIR_GROUP_SCHED
909 bool "Group scheduling for SCHED_OTHER"
910 depends on CGROUP_SCHED
911 default CGROUP_SCHED
912
ab84d31e
PT
913config CFS_BANDWIDTH
914 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
ab84d31e
PT
915 depends on FAIR_GROUP_SCHED
916 default n
917 help
918 This option allows users to define CPU bandwidth rates (limits) for
919 tasks running within the fair group scheduler. Groups with no limit
920 set are considered to be unconstrained and will run with no
921 restriction.
d6a3b247 922 See Documentation/scheduler/sched-bwc.rst for more information.
ab84d31e 923
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DG
924config RT_GROUP_SCHED
925 bool "Group scheduling for SCHED_RR/FIFO"
7c941438
DG
926 depends on CGROUP_SCHED
927 default n
928 help
929 This feature lets you explicitly allocate real CPU bandwidth
32bd7eb5 930 to task groups. If enabled, it will also make it impossible to
7c941438
DG
931 schedule realtime tasks for non-root users until you allocate
932 realtime bandwidth for them.
d6a3b247 933 See Documentation/scheduler/sched-rt-group.rst for more information.
7c941438
DG
934
935endif #CGROUP_SCHED
936
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PB
937config UCLAMP_TASK_GROUP
938 bool "Utilization clamping per group of tasks"
939 depends on CGROUP_SCHED
940 depends on UCLAMP_TASK
941 default n
942 help
943 This feature enables the scheduler to track the clamped utilization
944 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
945
946 When this option is enabled, the user can specify a min and max
947 CPU bandwidth which is allowed for each single task in a group.
948 The max bandwidth allows to clamp the maximum frequency a task
949 can use, while the min bandwidth allows to define a minimum
950 frequency a task will always use.
951
952 When task group based utilization clamping is enabled, an eventually
953 specified task-specific clamp value is constrained by the cgroup
954 specified clamp value. Both minimum and maximum task clamping cannot
955 be bigger than the corresponding clamping defined at task group level.
956
957 If in doubt, say N.
958
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959config CGROUP_PIDS
960 bool "PIDs controller"
961 help
962 Provides enforcement of process number limits in the scope of a
963 cgroup. Any attempt to fork more processes than is allowed in the
964 cgroup will fail. PIDs are fundamentally a global resource because it
965 is fairly trivial to reach PID exhaustion before you reach even a
966 conservative kmemcg limit. As a result, it is possible to grind a
967 system to halt without being limited by other cgroup policies. The
6cc578df 968 PIDs controller is designed to stop this from happening.
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969
970 It should be noted that organisational operations (such as attaching
98076833 971 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
6bf024e6
JW
972 since the PIDs limit only affects a process's ability to fork, not to
973 attach to a cgroup.
974
39d3e758
PP
975config CGROUP_RDMA
976 bool "RDMA controller"
977 help
978 Provides enforcement of RDMA resources defined by IB stack.
979 It is fairly easy for consumers to exhaust RDMA resources, which
980 can result into resource unavailability to other consumers.
981 RDMA controller is designed to stop this from happening.
982 Attaching processes with active RDMA resources to the cgroup
983 hierarchy is allowed even if can cross the hierarchy's limit.
984
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985config CGROUP_FREEZER
986 bool "Freezer controller"
987 help
988 Provides a way to freeze and unfreeze all tasks in a
989 cgroup.
990
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JW
991 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
992 controller includes important in-kernel memory consumers per default.
993
994 If you're using cgroup2, say N.
995
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996config CGROUP_HUGETLB
997 bool "HugeTLB controller"
998 depends on HUGETLB_PAGE
999 select PAGE_COUNTER
afc24d49 1000 default n
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JW
1001 help
1002 Provides a cgroup controller for HugeTLB pages.
1003 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1004 The limit is enforced during page fault. Since HugeTLB doesn't
1005 support page reclaim, enforcing the limit at page fault time implies
1006 that, the application will get SIGBUS signal if it tries to access
1007 HugeTLB pages beyond its limit. This requires the application to know
1008 beforehand how much HugeTLB pages it would require for its use. The
1009 control group is tracked in the third page lru pointer. This means
1010 that we cannot use the controller with huge page less than 3 pages.
afc24d49 1011
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1012config CPUSETS
1013 bool "Cpuset controller"
e1d4eeec 1014 depends on SMP
6bf024e6
JW
1015 help
1016 This option will let you create and manage CPUSETs which
1017 allow dynamically partitioning a system into sets of CPUs and
1018 Memory Nodes and assigning tasks to run only within those sets.
1019 This is primarily useful on large SMP or NUMA systems.
afc24d49 1020
6bf024e6 1021 Say N if unsure.
afc24d49 1022
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JW
1023config PROC_PID_CPUSET
1024 bool "Include legacy /proc/<pid>/cpuset file"
1025 depends on CPUSETS
1026 default y
afc24d49 1027
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JW
1028config CGROUP_DEVICE
1029 bool "Device controller"
1030 help
1031 Provides a cgroup controller implementing whitelists for
1032 devices which a process in the cgroup can mknod or open.
1033
1034config CGROUP_CPUACCT
1035 bool "Simple CPU accounting controller"
1036 help
1037 Provides a simple controller for monitoring the
1038 total CPU consumed by the tasks in a cgroup.
1039
1040config CGROUP_PERF
1041 bool "Perf controller"
1042 depends on PERF_EVENTS
1043 help
1044 This option extends the perf per-cpu mode to restrict monitoring
1045 to threads which belong to the cgroup specified and run on the
6546b19f
NK
1046 designated cpu. Or this can be used to have cgroup ID in samples
1047 so that it can monitor performance events among cgroups.
6bf024e6
JW
1048
1049 Say N if unsure.
1050
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DM
1051config CGROUP_BPF
1052 bool "Support for eBPF programs attached to cgroups"
483c4933
AL
1053 depends on BPF_SYSCALL
1054 select SOCK_CGROUP_DATA
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DM
1055 help
1056 Allow attaching eBPF programs to a cgroup using the bpf(2)
1057 syscall command BPF_PROG_ATTACH.
1058
1059 In which context these programs are accessed depends on the type
1060 of attachment. For instance, programs that are attached using
1061 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1062 inet sockets.
1063
6bf024e6 1064config CGROUP_DEBUG
23b0be48 1065 bool "Debug controller"
afc24d49 1066 default n
23b0be48 1067 depends on DEBUG_KERNEL
6bf024e6
JW
1068 help
1069 This option enables a simple controller that exports
23b0be48
WL
1070 debugging information about the cgroups framework. This
1071 controller is for control cgroup debugging only. Its
1072 interfaces are not stable.
afc24d49 1073
6bf024e6 1074 Say N.
89e9b9e0 1075
73b35147
AB
1076config SOCK_CGROUP_DATA
1077 bool
1078 default n
1079
23964d2d 1080endif # CGROUPS
c077719b 1081
8dd2a82c 1082menuconfig NAMESPACES
6a108a14 1083 bool "Namespaces support" if EXPERT
2813893f 1084 depends on MULTIUSER
6a108a14 1085 default !EXPERT
c5289a69
PE
1086 help
1087 Provides the way to make tasks work with different objects using
1088 the same id. For example same IPC id may refer to different objects
1089 or same user id or pid may refer to different tasks when used in
1090 different namespaces.
1091
8dd2a82c
DL
1092if NAMESPACES
1093
58bfdd6d
PE
1094config UTS_NS
1095 bool "UTS namespace"
17a6d441 1096 default y
58bfdd6d
PE
1097 help
1098 In this namespace tasks see different info provided with the
1099 uname() system call
1100
769071ac
AV
1101config TIME_NS
1102 bool "TIME namespace"
660fd04f 1103 depends on GENERIC_VDSO_TIME_NS
769071ac
AV
1104 default y
1105 help
1106 In this namespace boottime and monotonic clocks can be set.
1107 The time will keep going with the same pace.
1108
ae5e1b22
PE
1109config IPC_NS
1110 bool "IPC namespace"
8dd2a82c 1111 depends on (SYSVIPC || POSIX_MQUEUE)
17a6d441 1112 default y
ae5e1b22
PE
1113 help
1114 In this namespace tasks work with IPC ids which correspond to
614b84cf 1115 different IPC objects in different namespaces.
ae5e1b22 1116
aee16ce7 1117config USER_NS
19c92399 1118 bool "User namespace"
5673a94c 1119 default n
aee16ce7
PE
1120 help
1121 This allows containers, i.e. vservers, to use user namespaces
1122 to provide different user info for different servers.
e11f0ae3
EB
1123
1124 When user namespaces are enabled in the kernel it is
d886f4e4
JW
1125 recommended that the MEMCG option also be enabled and that
1126 user-space use the memory control groups to limit the amount
1127 of memory a memory unprivileged users can use.
e11f0ae3 1128
aee16ce7
PE
1129 If unsure, say N.
1130
74bd59bb 1131config PID_NS
9bd38c2c 1132 bool "PID Namespaces"
17a6d441 1133 default y
74bd59bb 1134 help
12d2b8f9 1135 Support process id namespaces. This allows having multiple
692105b8 1136 processes with the same pid as long as they are in different
74bd59bb
PE
1137 pid namespaces. This is a building block of containers.
1138
d6eb633f
MH
1139config NET_NS
1140 bool "Network namespace"
8dd2a82c 1141 depends on NET
17a6d441 1142 default y
d6eb633f
MH
1143 help
1144 Allow user space to create what appear to be multiple instances
1145 of the network stack.
1146
8dd2a82c
DL
1147endif # NAMESPACES
1148
5cb366bb
AR
1149config CHECKPOINT_RESTORE
1150 bool "Checkpoint/restore support"
1151 select PROC_CHILDREN
1152 default n
1153 help
1154 Enables additional kernel features in a sake of checkpoint/restore.
1155 In particular it adds auxiliary prctl codes to setup process text,
1156 data and heap segment sizes, and a few additional /proc filesystem
1157 entries.
1158
1159 If unsure, say N here.
1160
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MG
1161config SCHED_AUTOGROUP
1162 bool "Automatic process group scheduling"
5091faa4
MG
1163 select CGROUPS
1164 select CGROUP_SCHED
1165 select FAIR_GROUP_SCHED
1166 help
1167 This option optimizes the scheduler for common desktop workloads by
1168 automatically creating and populating task groups. This separation
1169 of workloads isolates aggressive CPU burners (like build jobs) from
1170 desktop applications. Task group autogeneration is currently based
1171 upon task session.
1172
7af37bec 1173config SYSFS_DEPRECATED
5d6a4ea5 1174 bool "Enable deprecated sysfs features to support old userspace tools"
7af37bec
DL
1175 depends on SYSFS
1176 default n
1177 help
1178 This option adds code that switches the layout of the "block" class
1179 devices, to not show up in /sys/class/block/, but only in
1180 /sys/block/.
1181
1182 This switch is only active when the sysfs.deprecated=1 boot option is
1183 passed or the SYSFS_DEPRECATED_V2 option is set.
1184
1185 This option allows new kernels to run on old distributions and tools,
1186 which might get confused by /sys/class/block/. Since 2007/2008 all
1187 major distributions and tools handle this just fine.
1188
1189 Recent distributions and userspace tools after 2009/2010 depend on
1190 the existence of /sys/class/block/, and will not work with this
1191 option enabled.
1192
1193 Only if you are using a new kernel on an old distribution, you might
1194 need to say Y here.
1195
1196config SYSFS_DEPRECATED_V2
5d6a4ea5 1197 bool "Enable deprecated sysfs features by default"
7af37bec
DL
1198 default n
1199 depends on SYSFS
1200 depends on SYSFS_DEPRECATED
1201 help
1202 Enable deprecated sysfs by default.
1203
1204 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1205 option.
1206
1207 Only if you are using a new kernel on an old distribution, you might
1208 need to say Y here. Even then, odds are you would not need it
1209 enabled, you can always pass the boot option if absolutely necessary.
1210
1211config RELAY
1212 bool "Kernel->user space relay support (formerly relayfs)"
26b5679e 1213 select IRQ_WORK
7af37bec
DL
1214 help
1215 This option enables support for relay interface support in
1216 certain file systems (such as debugfs).
1217 It is designed to provide an efficient mechanism for tools and
1218 facilities to relay large amounts of data from kernel space to
1219 user space.
1220
1221 If unsure, say N.
1222
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1223config BLK_DEV_INITRD
1224 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
f991633d
DG
1225 help
1226 The initial RAM filesystem is a ramfs which is loaded by the
1227 boot loader (loadlin or lilo) and that is mounted as root
1228 before the normal boot procedure. It is typically used to
1229 load modules needed to mount the "real" root file system,
8c27ceff 1230 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
f991633d
DG
1231
1232 If RAM disk support (BLK_DEV_RAM) is also included, this
1233 also enables initial RAM disk (initrd) support and adds
1234 15 Kbytes (more on some other architectures) to the kernel size.
1235
1236 If unsure say Y.
1237
c33df4ea
JPS
1238if BLK_DEV_INITRD
1239
dbec4866
SR
1240source "usr/Kconfig"
1241
c33df4ea
JPS
1242endif
1243
76db5a27
MH
1244config BOOT_CONFIG
1245 bool "Boot config support"
2910b5aa 1246 select BLK_DEV_INITRD
76db5a27
MH
1247 help
1248 Extra boot config allows system admin to pass a config file as
1249 complemental extension of kernel cmdline when booting.
0947db01 1250 The boot config file must be attached at the end of initramfs
85c46b78 1251 with checksum, size and magic word.
0947db01 1252 See <file:Documentation/admin-guide/bootconfig.rst> for details.
76db5a27
MH
1253
1254 If unsure, say Y.
1255
877417e6
AB
1256choice
1257 prompt "Compiler optimization level"
2cc3ce24 1258 default CC_OPTIMIZE_FOR_PERFORMANCE
877417e6
AB
1259
1260config CC_OPTIMIZE_FOR_PERFORMANCE
15f5db60 1261 bool "Optimize for performance (-O2)"
877417e6
AB
1262 help
1263 This is the default optimization level for the kernel, building
1264 with the "-O2" compiler flag for best performance and most
1265 helpful compile-time warnings.
1266
15f5db60
MY
1267config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1268 bool "Optimize more for performance (-O3)"
1269 depends on ARC
c45b4f1f 1270 help
15f5db60
MY
1271 Choosing this option will pass "-O3" to your compiler to optimize
1272 the kernel yet more for performance.
c45b4f1f 1273
c45b4f1f 1274config CC_OPTIMIZE_FOR_SIZE
15f5db60 1275 bool "Optimize for size (-Os)"
c45b4f1f 1276 help
ce3b487f
MY
1277 Choosing this option will pass "-Os" to your compiler resulting
1278 in a smaller kernel.
c45b4f1f 1279
877417e6
AB
1280endchoice
1281
5d20ee31
NP
1282config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1283 bool
1284 help
1285 This requires that the arch annotates or otherwise protects
1286 its external entry points from being discarded. Linker scripts
1287 must also merge .text.*, .data.*, and .bss.* correctly into
1288 output sections. Care must be taken not to pull in unrelated
1289 sections (e.g., '.text.init'). Typically '.' in section names
1290 is used to distinguish them from label names / C identifiers.
1291
1292config LD_DEAD_CODE_DATA_ELIMINATION
1293 bool "Dead code and data elimination (EXPERIMENTAL)"
1294 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1295 depends on EXPERT
16fd20aa 1296 depends on !(FUNCTION_TRACER && CC_IS_GCC && GCC_VERSION < 40800)
e85d1d65
MY
1297 depends on $(cc-option,-ffunction-sections -fdata-sections)
1298 depends on $(ld-option,--gc-sections)
5d20ee31 1299 help
8b9d2712
MY
1300 Enable this if you want to do dead code and data elimination with
1301 the linker by compiling with -ffunction-sections -fdata-sections,
1302 and linking with --gc-sections.
5d20ee31
NP
1303
1304 This can reduce on disk and in-memory size of the kernel
1305 code and static data, particularly for small configs and
1306 on small systems. This has the possibility of introducing
1307 silently broken kernel if the required annotations are not
1308 present. This option is not well tested yet, so use at your
1309 own risk.
1310
0847062a
RD
1311config SYSCTL
1312 bool
1313
657a5209
MF
1314config HAVE_UID16
1315 bool
1316
1317config SYSCTL_EXCEPTION_TRACE
1318 bool
1319 help
1320 Enable support for /proc/sys/debug/exception-trace.
1321
1322config SYSCTL_ARCH_UNALIGN_NO_WARN
1323 bool
1324 help
1325 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1326 Allows arch to define/use @no_unaligned_warning to possibly warn
1327 about unaligned access emulation going on under the hood.
1328
1329config SYSCTL_ARCH_UNALIGN_ALLOW
1330 bool
1331 help
1332 Enable support for /proc/sys/kernel/unaligned-trap
1333 Allows arches to define/use @unaligned_enabled to runtime toggle
1334 the unaligned access emulation.
1335 see arch/parisc/kernel/unaligned.c for reference
1336
657a5209
MF
1337config HAVE_PCSPKR_PLATFORM
1338 bool
1339
f89b7755
AS
1340# interpreter that classic socket filters depend on
1341config BPF
1342 bool
1343
6a108a14
DR
1344menuconfig EXPERT
1345 bool "Configure standard kernel features (expert users)"
f505c553
JT
1346 # Unhide debug options, to make the on-by-default options visible
1347 select DEBUG_KERNEL
1da177e4
LT
1348 help
1349 This option allows certain base kernel options and settings
e8cf4e9c
KK
1350 to be disabled or tweaked. This is for specialized
1351 environments which can tolerate a "non-standard" kernel.
1352 Only use this if you really know what you are doing.
1da177e4 1353
ae81f9e3 1354config UID16
6a108a14 1355 bool "Enable 16-bit UID system calls" if EXPERT
2813893f 1356 depends on HAVE_UID16 && MULTIUSER
ae81f9e3
CE
1357 default y
1358 help
1359 This enables the legacy 16-bit UID syscall wrappers.
1360
2813893f
IM
1361config MULTIUSER
1362 bool "Multiple users, groups and capabilities support" if EXPERT
1363 default y
1364 help
1365 This option enables support for non-root users, groups and
1366 capabilities.
1367
1368 If you say N here, all processes will run with UID 0, GID 0, and all
1369 possible capabilities. Saying N here also compiles out support for
1370 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1371 setgid, and capset.
1372
1373 If unsure, say Y here.
1374
f6187769
FF
1375config SGETMASK_SYSCALL
1376 bool "sgetmask/ssetmask syscalls support" if EXPERT
a687a533 1377 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
f6187769
FF
1378 ---help---
1379 sys_sgetmask and sys_ssetmask are obsolete system calls
1380 no longer supported in libc but still enabled by default in some
1381 architectures.
1382
1383 If unsure, leave the default option here.
1384
6af9f7bf
FF
1385config SYSFS_SYSCALL
1386 bool "Sysfs syscall support" if EXPERT
1387 default y
1388 ---help---
1389 sys_sysfs is an obsolete system call no longer supported in libc.
1390 Note that disabling this option is more secure but might break
1391 compatibility with some systems.
1392
1393 If unsure say Y here.
1394
d1b069f5
RD
1395config FHANDLE
1396 bool "open by fhandle syscalls" if EXPERT
1397 select EXPORTFS
1398 default y
1399 help
1400 If you say Y here, a user level program will be able to map
1401 file names to handle and then later use the handle for
1402 different file system operations. This is useful in implementing
1403 userspace file servers, which now track files using handles instead
1404 of names. The handle would remain the same even if file names
1405 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1406 syscalls.
1407
baa73d9e
NP
1408config POSIX_TIMERS
1409 bool "Posix Clocks & timers" if EXPERT
1410 default y
1411 help
1412 This includes native support for POSIX timers to the kernel.
1413 Some embedded systems have no use for them and therefore they
1414 can be configured out to reduce the size of the kernel image.
1415
1416 When this option is disabled, the following syscalls won't be
1417 available: timer_create, timer_gettime: timer_getoverrun,
1418 timer_settime, timer_delete, clock_adjtime, getitimer,
1419 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1420 clock_getres and clock_nanosleep syscalls will be limited to
1421 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1422
1423 If unsure say y.
1424
d59745ce
MM
1425config PRINTK
1426 default y
6a108a14 1427 bool "Enable support for printk" if EXPERT
74876a98 1428 select IRQ_WORK
d59745ce
MM
1429 help
1430 This option enables normal printk support. Removing it
1431 eliminates most of the message strings from the kernel image
1432 and makes the kernel more or less silent. As this makes it
1433 very difficult to diagnose system problems, saying N here is
1434 strongly discouraged.
1435
42a0bb3f
PM
1436config PRINTK_NMI
1437 def_bool y
1438 depends on PRINTK
1439 depends on HAVE_NMI
1440
c8538a7a 1441config BUG
6a108a14 1442 bool "BUG() support" if EXPERT
c8538a7a
MM
1443 default y
1444 help
e8cf4e9c
KK
1445 Disabling this option eliminates support for BUG and WARN, reducing
1446 the size of your kernel image and potentially quietly ignoring
1447 numerous fatal conditions. You should only consider disabling this
1448 option for embedded systems with no facilities for reporting errors.
1449 Just say Y.
c8538a7a 1450
708e9a79 1451config ELF_CORE
046d662f 1452 depends on COREDUMP
708e9a79 1453 default y
6a108a14 1454 bool "Enable ELF core dumps" if EXPERT
708e9a79
MM
1455 help
1456 Enable support for generating core dumps. Disabling saves about 4k.
1457
8761f1ab 1458
e5e1d3cb 1459config PCSPKR_PLATFORM
6a108a14 1460 bool "Enable PC-Speaker support" if EXPERT
8761f1ab 1461 depends on HAVE_PCSPKR_PLATFORM
15f304b6 1462 select I8253_LOCK
e5e1d3cb
SS
1463 default y
1464 help
e8cf4e9c
KK
1465 This option allows to disable the internal PC-Speaker
1466 support, saving some memory.
e5e1d3cb 1467
1da177e4
LT
1468config BASE_FULL
1469 default y
6a108a14 1470 bool "Enable full-sized data structures for core" if EXPERT
1da177e4
LT
1471 help
1472 Disabling this option reduces the size of miscellaneous core
1473 kernel data structures. This saves memory on small machines,
1474 but may reduce performance.
1475
1476config FUTEX
6a108a14 1477 bool "Enable futex support" if EXPERT
1da177e4 1478 default y
bc2eecd7 1479 imply RT_MUTEXES
1da177e4
LT
1480 help
1481 Disabling this option will cause the kernel to be built without
1482 support for "fast userspace mutexes". The resulting kernel may not
1483 run glibc-based applications correctly.
1484
bc2eecd7
NP
1485config FUTEX_PI
1486 bool
1487 depends on FUTEX && RT_MUTEXES
1488 default y
1489
03b8c7b6
HC
1490config HAVE_FUTEX_CMPXCHG
1491 bool
62b4d204 1492 depends on FUTEX
03b8c7b6
HC
1493 help
1494 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1495 is implemented and always working. This removes a couple of runtime
1496 checks.
1497
1da177e4 1498config EPOLL
6a108a14 1499 bool "Enable eventpoll support" if EXPERT
1da177e4
LT
1500 default y
1501 help
1502 Disabling this option will cause the kernel to be built without
1503 support for epoll family of system calls.
1504
fba2afaa 1505config SIGNALFD
6a108a14 1506 bool "Enable signalfd() system call" if EXPERT
fba2afaa
DL
1507 default y
1508 help
1509 Enable the signalfd() system call that allows to receive signals
1510 on a file descriptor.
1511
1512 If unsure, say Y.
1513
b215e283 1514config TIMERFD
6a108a14 1515 bool "Enable timerfd() system call" if EXPERT
b215e283
DL
1516 default y
1517 help
1518 Enable the timerfd() system call that allows to receive timer
1519 events on a file descriptor.
1520
1521 If unsure, say Y.
1522
e1ad7468 1523config EVENTFD
6a108a14 1524 bool "Enable eventfd() system call" if EXPERT
e1ad7468
DL
1525 default y
1526 help
1527 Enable the eventfd() system call that allows to receive both
1528 kernel notification (ie. KAIO) or userspace notifications.
1529
1530 If unsure, say Y.
1531
1da177e4 1532config SHMEM
6a108a14 1533 bool "Use full shmem filesystem" if EXPERT
1da177e4
LT
1534 default y
1535 depends on MMU
1536 help
1537 The shmem is an internal filesystem used to manage shared memory.
1538 It is backed by swap and manages resource limits. It is also exported
1539 to userspace as tmpfs if TMPFS is enabled. Disabling this
1540 option replaces shmem and tmpfs with the much simpler ramfs code,
1541 which may be appropriate on small systems without swap.
1542
ebf3f09c 1543config AIO
6a108a14 1544 bool "Enable AIO support" if EXPERT
ebf3f09c
TP
1545 default y
1546 help
1547 This option enables POSIX asynchronous I/O which may by used
657a5209
MF
1548 by some high performance threaded applications. Disabling
1549 this option saves about 7k.
1550
2b188cc1
JA
1551config IO_URING
1552 bool "Enable IO uring support" if EXPERT
561fb04a 1553 select IO_WQ
2b188cc1
JA
1554 default y
1555 help
1556 This option enables support for the io_uring interface, enabling
1557 applications to submit and complete IO through submission and
1558 completion rings that are shared between the kernel and application.
1559
d3ac21ca
JT
1560config ADVISE_SYSCALLS
1561 bool "Enable madvise/fadvise syscalls" if EXPERT
1562 default y
1563 help
1564 This option enables the madvise and fadvise syscalls, used by
1565 applications to advise the kernel about their future memory or file
1566 usage, improving performance. If building an embedded system where no
1567 applications use these syscalls, you can disable this option to save
1568 space.
1569
5a281062
AA
1570config HAVE_ARCH_USERFAULTFD_WP
1571 bool
1572 help
1573 Arch has userfaultfd write protection support
1574
5b25b13a
MD
1575config MEMBARRIER
1576 bool "Enable membarrier() system call" if EXPERT
1577 default y
1578 help
1579 Enable the membarrier() system call that allows issuing memory
1580 barriers across all running threads, which can be used to distribute
1581 the cost of user-space memory barriers asymmetrically by transforming
1582 pairs of memory barriers into pairs consisting of membarrier() and a
1583 compiler barrier.
1584
1585 If unsure, say Y.
1586
d1b069f5 1587config KALLSYMS
e8cf4e9c
KK
1588 bool "Load all symbols for debugging/ksymoops" if EXPERT
1589 default y
1590 help
1591 Say Y here to let the kernel print out symbolic crash information and
1592 symbolic stack backtraces. This increases the size of the kernel
1593 somewhat, as all symbols have to be loaded into the kernel image.
d1b069f5
RD
1594
1595config KALLSYMS_ALL
1596 bool "Include all symbols in kallsyms"
1597 depends on DEBUG_KERNEL && KALLSYMS
1598 help
e8cf4e9c
KK
1599 Normally kallsyms only contains the symbols of functions for nicer
1600 OOPS messages and backtraces (i.e., symbols from the text and inittext
1601 sections). This is sufficient for most cases. And only in very rare
1602 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1603 names of variables from the data sections, etc).
d1b069f5 1604
e8cf4e9c
KK
1605 This option makes sure that all symbols are loaded into the kernel
1606 image (i.e., symbols from all sections) in cost of increased kernel
1607 size (depending on the kernel configuration, it may be 300KiB or
1608 something like this).
d1b069f5 1609
e8cf4e9c 1610 Say N unless you really need all symbols.
d1b069f5
RD
1611
1612config KALLSYMS_ABSOLUTE_PERCPU
1613 bool
1614 depends on KALLSYMS
1615 default X86_64 && SMP
1616
1617config KALLSYMS_BASE_RELATIVE
1618 bool
1619 depends on KALLSYMS
a687a533 1620 default !IA64
d1b069f5
RD
1621 help
1622 Instead of emitting them as absolute values in the native word size,
1623 emit the symbol references in the kallsyms table as 32-bit entries,
1624 each containing a relative value in the range [base, base + U32_MAX]
1625 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1626 an absolute value in the range [0, S32_MAX] or a relative value in the
1627 range [base, base + S32_MAX], where base is the lowest relative symbol
1628 address encountered in the image.
1629
1630 On 64-bit builds, this reduces the size of the address table by 50%,
1631 but more importantly, it results in entries whose values are build
1632 time constants, and no relocation pass is required at runtime to fix
1633 up the entries based on the runtime load address of the kernel.
1634
1635# end of the "standard kernel features (expert users)" menu
1636
1637# syscall, maps, verifier
fc611f47
KS
1638
1639config BPF_LSM
1640 bool "LSM Instrumentation with BPF"
4edf16b7 1641 depends on BPF_EVENTS
fc611f47
KS
1642 depends on BPF_SYSCALL
1643 depends on SECURITY
1644 depends on BPF_JIT
1645 help
1646 Enables instrumentation of the security hooks with eBPF programs for
1647 implementing dynamic MAC and Audit Policies.
1648
1649 If you are unsure how to answer this question, answer N.
1650
d1b069f5
RD
1651config BPF_SYSCALL
1652 bool "Enable bpf() system call"
d1b069f5 1653 select BPF
bae77c5e 1654 select IRQ_WORK
d1b069f5
RD
1655 default n
1656 help
1657 Enable the bpf() system call that allows to manipulate eBPF
1658 programs and maps via file descriptors.
1659
81c22041
DB
1660config ARCH_WANT_DEFAULT_BPF_JIT
1661 bool
1662
290af866
AS
1663config BPF_JIT_ALWAYS_ON
1664 bool "Permanently enable BPF JIT and remove BPF interpreter"
1665 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
1666 help
1667 Enables BPF JIT and removes BPF interpreter to avoid
1668 speculative execution of BPF instructions by the interpreter
1669
81c22041
DB
1670config BPF_JIT_DEFAULT_ON
1671 def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON
1672 depends on HAVE_EBPF_JIT && BPF_JIT
1673
d1b069f5
RD
1674config USERFAULTFD
1675 bool "Enable userfaultfd() system call"
d1b069f5
RD
1676 depends on MMU
1677 help
1678 Enable the userfaultfd() system call that allows to intercept and
1679 handle page faults in userland.
1680
3ccfebed
MD
1681config ARCH_HAS_MEMBARRIER_CALLBACKS
1682 bool
1683
70216e18
MD
1684config ARCH_HAS_MEMBARRIER_SYNC_CORE
1685 bool
1686
d7822b1e
MD
1687config RSEQ
1688 bool "Enable rseq() system call" if EXPERT
1689 default y
1690 depends on HAVE_RSEQ
1691 select MEMBARRIER
1692 help
1693 Enable the restartable sequences system call. It provides a
1694 user-space cache for the current CPU number value, which
1695 speeds up getting the current CPU number from user-space,
1696 as well as an ABI to speed up user-space operations on
1697 per-CPU data.
1698
1699 If unsure, say Y.
1700
1701config DEBUG_RSEQ
1702 default n
1703 bool "Enabled debugging of rseq() system call" if EXPERT
1704 depends on RSEQ && DEBUG_KERNEL
1705 help
1706 Enable extra debugging checks for the rseq system call.
1707
1708 If unsure, say N.
1709
6befe5f6
RD
1710config EMBEDDED
1711 bool "Embedded system"
5d2acfc7 1712 option allnoconfig_y
6befe5f6
RD
1713 select EXPERT
1714 help
1715 This option should be enabled if compiling the kernel for
1716 an embedded system so certain expert options are available
1717 for configuration.
1718
cdd6c482 1719config HAVE_PERF_EVENTS
0793a61d 1720 bool
018df72d
MF
1721 help
1722 See tools/perf/design.txt for details.
0793a61d 1723
906010b2
PZ
1724config PERF_USE_VMALLOC
1725 bool
1726 help
1727 See tools/perf/design.txt for details
1728
ad90a3de 1729config PC104
424529fb 1730 bool "PC/104 support" if EXPERT
ad90a3de
WBG
1731 help
1732 Expose PC/104 form factor device drivers and options available for
1733 selection and configuration. Enable this option if your target
1734 machine has a PC/104 bus.
1735
57c0c15b 1736menu "Kernel Performance Events And Counters"
0793a61d 1737
cdd6c482 1738config PERF_EVENTS
57c0c15b 1739 bool "Kernel performance events and counters"
392d65a9 1740 default y if PROFILING
cdd6c482 1741 depends on HAVE_PERF_EVENTS
e360adbe 1742 select IRQ_WORK
83fe27ea 1743 select SRCU
0793a61d 1744 help
57c0c15b
IM
1745 Enable kernel support for various performance events provided
1746 by software and hardware.
0793a61d 1747
dd77038d 1748 Software events are supported either built-in or via the
57c0c15b 1749 use of generic tracepoints.
0793a61d 1750
57c0c15b
IM
1751 Most modern CPUs support performance events via performance
1752 counter registers. These registers count the number of certain
0793a61d
TG
1753 types of hw events: such as instructions executed, cachemisses
1754 suffered, or branches mis-predicted - without slowing down the
1755 kernel or applications. These registers can also trigger interrupts
1756 when a threshold number of events have passed - and can thus be
1757 used to profile the code that runs on that CPU.
1758
57c0c15b 1759 The Linux Performance Event subsystem provides an abstraction of
dd77038d 1760 these software and hardware event capabilities, available via a
57c0c15b 1761 system call and used by the "perf" utility in tools/perf/. It
0793a61d
TG
1762 provides per task and per CPU counters, and it provides event
1763 capabilities on top of those.
1764
1765 Say Y if unsure.
1766
906010b2
PZ
1767config DEBUG_PERF_USE_VMALLOC
1768 default n
1769 bool "Debug: use vmalloc to back perf mmap() buffers"
cb307113 1770 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
906010b2
PZ
1771 select PERF_USE_VMALLOC
1772 help
e8cf4e9c 1773 Use vmalloc memory to back perf mmap() buffers.
906010b2 1774
e8cf4e9c
KK
1775 Mostly useful for debugging the vmalloc code on platforms
1776 that don't require it.
906010b2 1777
e8cf4e9c 1778 Say N if unsure.
906010b2 1779
0793a61d
TG
1780endmenu
1781
f8891e5e
CL
1782config VM_EVENT_COUNTERS
1783 default y
6a108a14 1784 bool "Enable VM event counters for /proc/vmstat" if EXPERT
f8891e5e 1785 help
2aea4fb6
PJ
1786 VM event counters are needed for event counts to be shown.
1787 This option allows the disabling of the VM event counters
6a108a14 1788 on EXPERT systems. /proc/vmstat will only show page counts
2aea4fb6 1789 if VM event counters are disabled.
f8891e5e 1790
41ecc55b
CL
1791config SLUB_DEBUG
1792 default y
6a108a14 1793 bool "Enable SLUB debugging support" if EXPERT
f6acb635 1794 depends on SLUB && SYSFS
41ecc55b
CL
1795 help
1796 SLUB has extensive debug support features. Disabling these can
1797 result in significant savings in code size. This also disables
1798 SLUB sysfs support. /sys/slab will not exist and there will be
1799 no support for cache validation etc.
1800
1663f26d
TH
1801config SLUB_MEMCG_SYSFS_ON
1802 default n
1803 bool "Enable memcg SLUB sysfs support by default" if EXPERT
1804 depends on SLUB && SYSFS && MEMCG
1805 help
1806 SLUB creates a directory under /sys/kernel/slab for each
1807 allocation cache to host info and debug files. If memory
1808 cgroup is enabled, each cache can have per memory cgroup
1809 caches. SLUB can create the same sysfs directories for these
1810 caches under /sys/kernel/slab/CACHE/cgroup but it can lead
1811 to a very high number of debug files being created. This is
1812 controlled by slub_memcg_sysfs boot parameter and this
1813 config option determines the parameter's default value.
1814
b943c460
RD
1815config COMPAT_BRK
1816 bool "Disable heap randomization"
1817 default y
1818 help
1819 Randomizing heap placement makes heap exploits harder, but it
1820 also breaks ancient binaries (including anything libc5 based).
1821 This option changes the bootup default to heap randomization
692105b8 1822 disabled, and can be overridden at runtime by setting
b943c460
RD
1823 /proc/sys/kernel/randomize_va_space to 2.
1824
1825 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1826
81819f0f
CL
1827choice
1828 prompt "Choose SLAB allocator"
a0acd820 1829 default SLUB
81819f0f
CL
1830 help
1831 This option allows to select a slab allocator.
1832
1833config SLAB
1834 bool "SLAB"
04385fc5 1835 select HAVE_HARDENED_USERCOPY_ALLOCATOR
81819f0f
CL
1836 help
1837 The regular slab allocator that is established and known to work
34013886 1838 well in all environments. It organizes cache hot objects in
02f56210 1839 per cpu and per node queues.
81819f0f
CL
1840
1841config SLUB
81819f0f 1842 bool "SLUB (Unqueued Allocator)"
ed18adc1 1843 select HAVE_HARDENED_USERCOPY_ALLOCATOR
81819f0f
CL
1844 help
1845 SLUB is a slab allocator that minimizes cache line usage
1846 instead of managing queues of cached objects (SLAB approach).
1847 Per cpu caching is realized using slabs of objects instead
1848 of queues of objects. SLUB can use memory efficiently
02f56210
SA
1849 and has enhanced diagnostics. SLUB is the default choice for
1850 a slab allocator.
81819f0f
CL
1851
1852config SLOB
6a108a14 1853 depends on EXPERT
81819f0f
CL
1854 bool "SLOB (Simple Allocator)"
1855 help
37291458
MM
1856 SLOB replaces the stock allocator with a drastically simpler
1857 allocator. SLOB is generally more space efficient but
1858 does not perform as well on large systems.
81819f0f
CL
1859
1860endchoice
1861
7660a6fd
KC
1862config SLAB_MERGE_DEFAULT
1863 bool "Allow slab caches to be merged"
1864 default y
1865 help
1866 For reduced kernel memory fragmentation, slab caches can be
1867 merged when they share the same size and other characteristics.
1868 This carries a risk of kernel heap overflows being able to
1869 overwrite objects from merged caches (and more easily control
1870 cache layout), which makes such heap attacks easier to exploit
1871 by attackers. By keeping caches unmerged, these kinds of exploits
1872 can usually only damage objects in the same cache. To disable
1873 merging at runtime, "slab_nomerge" can be passed on the kernel
1874 command line.
1875
c7ce4f60
TG
1876config SLAB_FREELIST_RANDOM
1877 default n
210e7a43 1878 depends on SLAB || SLUB
c7ce4f60
TG
1879 bool "SLAB freelist randomization"
1880 help
210e7a43 1881 Randomizes the freelist order used on creating new pages. This
c7ce4f60
TG
1882 security feature reduces the predictability of the kernel slab
1883 allocator against heap overflows.
1884
2482ddec
KC
1885config SLAB_FREELIST_HARDENED
1886 bool "Harden slab freelist metadata"
1887 depends on SLUB
1888 help
1889 Many kernel heap attacks try to target slab cache metadata and
1890 other infrastructure. This options makes minor performance
92bae787 1891 sacrifices to harden the kernel slab allocator against common
2482ddec
KC
1892 freelist exploit methods.
1893
e900a918
DW
1894config SHUFFLE_PAGE_ALLOCATOR
1895 bool "Page allocator randomization"
1896 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1897 help
1898 Randomization of the page allocator improves the average
1899 utilization of a direct-mapped memory-side-cache. See section
1900 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1901 6.2a specification for an example of how a platform advertises
1902 the presence of a memory-side-cache. There are also incidental
1903 security benefits as it reduces the predictability of page
1904 allocations to compliment SLAB_FREELIST_RANDOM, but the
1905 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1906 10th order of pages is selected based on cache utilization
1907 benefits on x86.
1908
1909 While the randomization improves cache utilization it may
1910 negatively impact workloads on platforms without a cache. For
1911 this reason, by default, the randomization is enabled only
1912 after runtime detection of a direct-mapped memory-side-cache.
1913 Otherwise, the randomization may be force enabled with the
1914 'page_alloc.shuffle' kernel command line parameter.
1915
1916 Say Y if unsure.
1917
345c905d
JK
1918config SLUB_CPU_PARTIAL
1919 default y
b39ffbf8 1920 depends on SLUB && SMP
345c905d
JK
1921 bool "SLUB per cpu partial cache"
1922 help
92bae787 1923 Per cpu partial caches accelerate objects allocation and freeing
345c905d
JK
1924 that is local to a processor at the price of more indeterminism
1925 in the latency of the free. On overflow these caches will be cleared
1926 which requires the taking of locks that may cause latency spikes.
1927 Typically one would choose no for a realtime system.
1928
ea637639
JZ
1929config MMAP_ALLOW_UNINITIALIZED
1930 bool "Allow mmapped anonymous memory to be uninitialized"
6a108a14 1931 depends on EXPERT && !MMU
ea637639
JZ
1932 default n
1933 help
1934 Normally, and according to the Linux spec, anonymous memory obtained
3903bf94 1935 from mmap() has its contents cleared before it is passed to
ea637639
JZ
1936 userspace. Enabling this config option allows you to request that
1937 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1938 providing a huge performance boost. If this option is not enabled,
1939 then the flag will be ignored.
1940
1941 This is taken advantage of by uClibc's malloc(), and also by
1942 ELF-FDPIC binfmt's brk and stack allocator.
1943
1944 Because of the obvious security issues, this option should only be
1945 enabled on embedded devices where you control what is run in
1946 userspace. Since that isn't generally a problem on no-MMU systems,
1947 it is normally safe to say Y here.
1948
1949 See Documentation/nommu-mmap.txt for more information.
1950
091f6e26
DH
1951config SYSTEM_DATA_VERIFICATION
1952 def_bool n
1953 select SYSTEM_TRUSTED_KEYRING
1954 select KEYS
1955 select CRYPTO
d43de6c7 1956 select CRYPTO_RSA
091f6e26
DH
1957 select ASYMMETRIC_KEY_TYPE
1958 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
091f6e26
DH
1959 select ASN1
1960 select OID_REGISTRY
1961 select X509_CERTIFICATE_PARSER
1962 select PKCS7_MESSAGE_PARSER
82c04ff8 1963 help
091f6e26
DH
1964 Provide PKCS#7 message verification using the contents of the system
1965 trusted keyring to provide public keys. This then can be used for
1966 module verification, kexec image verification and firmware blob
1967 verification.
82c04ff8 1968
125e5645 1969config PROFILING
b309a294 1970 bool "Profiling support"
125e5645
MD
1971 help
1972 Say Y here to enable the extended profiling support mechanisms used
1973 by profilers such as OProfile.
1974
5f87f112
IM
1975#
1976# Place an empty function call at each tracepoint site. Can be
1977# dynamically changed for a probe function.
1978#
97e1c18e 1979config TRACEPOINTS
5f87f112 1980 bool
97e1c18e 1981
1da177e4
LT
1982endmenu # General setup
1983
1572497c
CH
1984source "arch/Kconfig"
1985
ae81f9e3 1986config RT_MUTEXES
6341e62b 1987 bool
ae81f9e3 1988
1da177e4
LT
1989config BASE_SMALL
1990 int
1991 default 0 if BASE_FULL
1992 default 1 if !BASE_FULL
1993
c8424e77
TJB
1994config MODULE_SIG_FORMAT
1995 def_bool n
1996 select SYSTEM_DATA_VERIFICATION
1997
66da5733 1998menuconfig MODULES
1da177e4 1999 bool "Enable loadable module support"
11097a03 2000 option modules
1da177e4
LT
2001 help
2002 Kernel modules are small pieces of compiled code which can
2003 be inserted in the running kernel, rather than being
2004 permanently built into the kernel. You use the "modprobe"
2005 tool to add (and sometimes remove) them. If you say Y here,
2006 many parts of the kernel can be built as modules (by
2007 answering M instead of Y where indicated): this is most
2008 useful for infrequently used options which are not required
2009 for booting. For more information, see the man pages for
2010 modprobe, lsmod, modinfo, insmod and rmmod.
2011
2012 If you say Y here, you will need to run "make
2013 modules_install" to put the modules under /lib/modules/
2014 where modprobe can find them (you may need to be root to do
2015 this).
2016
2017 If unsure, say Y.
2018
0b0de144
RD
2019if MODULES
2020
826e4506
LT
2021config MODULE_FORCE_LOAD
2022 bool "Forced module loading"
826e4506
LT
2023 default n
2024 help
91e37a79
RR
2025 Allow loading of modules without version information (ie. modprobe
2026 --force). Forced module loading sets the 'F' (forced) taint flag and
2027 is usually a really bad idea.
826e4506 2028
1da177e4
LT
2029config MODULE_UNLOAD
2030 bool "Module unloading"
1da177e4
LT
2031 help
2032 Without this option you will not be able to unload any
2033 modules (note that some modules may not be unloadable
f7f5b675
DV
2034 anyway), which makes your kernel smaller, faster
2035 and simpler. If unsure, say Y.
1da177e4
LT
2036
2037config MODULE_FORCE_UNLOAD
2038 bool "Forced module unloading"
19c92399 2039 depends on MODULE_UNLOAD
1da177e4
LT
2040 help
2041 This option allows you to force a module to unload, even if the
2042 kernel believes it is unsafe: the kernel will remove the module
2043 without waiting for anyone to stop using it (using the -f option to
2044 rmmod). This is mainly for kernel developers and desperate users.
2045 If unsure, say N.
2046
1da177e4 2047config MODVERSIONS
0d541643 2048 bool "Module versioning support"
1da177e4
LT
2049 help
2050 Usually, you have to use modules compiled with your kernel.
2051 Saying Y here makes it sometimes possible to use modules
2052 compiled for different kernels, by adding enough information
2053 to the modules to (hopefully) spot any changes which would
2054 make them incompatible with the kernel you are running. If
2055 unsure, say N.
2056
2ff2b7ec
MY
2057config ASM_MODVERSIONS
2058 bool
2059 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2060 help
2061 This enables module versioning for exported symbols also from
2062 assembly. This can be enabled only when the target architecture
2063 supports it.
2064
56067812
AB
2065config MODULE_REL_CRCS
2066 bool
2067 depends on MODVERSIONS
2068
1da177e4
LT
2069config MODULE_SRCVERSION_ALL
2070 bool "Source checksum for all modules"
1da177e4
LT
2071 help
2072 Modules which contain a MODULE_VERSION get an extra "srcversion"
2073 field inserted into their modinfo section, which contains a
2074 sum of the source files which made it. This helps maintainers
2075 see exactly which source was used to build a module (since
2076 others sometimes change the module source without updating
2077 the version). With this option, such a "srcversion" field
2078 will be created for all modules. If unsure, say N.
2079
106a4ee2
RR
2080config MODULE_SIG
2081 bool "Module signature verification"
c8424e77 2082 select MODULE_SIG_FORMAT
106a4ee2
RR
2083 help
2084 Check modules for valid signatures upon load: the signature
2085 is simply appended to the module. For more information see
cbdc8217 2086 <file:Documentation/admin-guide/module-signing.rst>.
106a4ee2 2087
228c37ff
DH
2088 Note that this option adds the OpenSSL development packages as a
2089 kernel build dependency so that the signing tool can use its crypto
2090 library.
2091
49fcf732
DH
2092 You should enable this option if you wish to use either
2093 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2094 another LSM - otherwise unsigned modules will be loadable regardless
2095 of the lockdown policy.
2096
ea0b6dcf
DH
2097 !!!WARNING!!! If you enable this option, you MUST make sure that the
2098 module DOES NOT get stripped after being signed. This includes the
2099 debuginfo strip done by some packagers (such as rpmbuild) and
2100 inclusion into an initramfs that wants the module size reduced.
2101
106a4ee2
RR
2102config MODULE_SIG_FORCE
2103 bool "Require modules to be validly signed"
2104 depends on MODULE_SIG
2105 help
2106 Reject unsigned modules or signed modules for which we don't have a
2107 key. Without this, such modules will simply taint the kernel.
ea0b6dcf 2108
d9d8d7ed
MM
2109config MODULE_SIG_ALL
2110 bool "Automatically sign all modules"
2111 default y
2112 depends on MODULE_SIG
2113 help
2114 Sign all modules during make modules_install. Without this option,
2115 modules must be signed manually, using the scripts/sign-file tool.
2116
2117comment "Do not forget to sign required modules with scripts/sign-file"
2118 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2119
ea0b6dcf
DH
2120choice
2121 prompt "Which hash algorithm should modules be signed with?"
2122 depends on MODULE_SIG
2123 help
2124 This determines which sort of hashing algorithm will be used during
2125 signature generation. This algorithm _must_ be built into the kernel
2126 directly so that signature verification can take place. It is not
2127 possible to load a signed module containing the algorithm to check
2128 the signature on that module.
2129
2130config MODULE_SIG_SHA1
2131 bool "Sign modules with SHA-1"
2132 select CRYPTO_SHA1
2133
2134config MODULE_SIG_SHA224
2135 bool "Sign modules with SHA-224"
2136 select CRYPTO_SHA256
2137
2138config MODULE_SIG_SHA256
2139 bool "Sign modules with SHA-256"
2140 select CRYPTO_SHA256
2141
2142config MODULE_SIG_SHA384
2143 bool "Sign modules with SHA-384"
2144 select CRYPTO_SHA512
2145
2146config MODULE_SIG_SHA512
2147 bool "Sign modules with SHA-512"
2148 select CRYPTO_SHA512
2149
2150endchoice
2151
22753674
MM
2152config MODULE_SIG_HASH
2153 string
2154 depends on MODULE_SIG
2155 default "sha1" if MODULE_SIG_SHA1
2156 default "sha224" if MODULE_SIG_SHA224
2157 default "sha256" if MODULE_SIG_SHA256
2158 default "sha384" if MODULE_SIG_SHA384
2159 default "sha512" if MODULE_SIG_SHA512
2160
beb50df3
BJ
2161config MODULE_COMPRESS
2162 bool "Compress modules on installation"
beb50df3 2163 help
beb50df3 2164
b6c09b51
RR
2165 Compresses kernel modules when 'make modules_install' is run; gzip or
2166 xz depending on "Compression algorithm" below.
beb50df3 2167
b6c09b51 2168 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
beb50df3 2169
b6c09b51
RR
2170 Out-of-tree kernel modules installed using Kbuild will also be
2171 compressed upon installation.
beb50df3 2172
b6c09b51
RR
2173 Note: for modules inside an initrd or initramfs, it's more efficient
2174 to compress the whole initrd or initramfs instead.
beb50df3 2175
b6c09b51
RR
2176 Note: This is fully compatible with signed modules.
2177
2178 If in doubt, say N.
beb50df3
BJ
2179
2180choice
2181 prompt "Compression algorithm"
2182 depends on MODULE_COMPRESS
2183 default MODULE_COMPRESS_GZIP
2184 help
2185 This determines which sort of compression will be used during
2186 'make modules_install'.
2187
2188 GZIP (default) and XZ are supported.
2189
2190config MODULE_COMPRESS_GZIP
2191 bool "GZIP"
2192
2193config MODULE_COMPRESS_XZ
2194 bool "XZ"
2195
2196endchoice
2197
3d52ec5e
MM
2198config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2199 bool "Allow loading of modules with missing namespace imports"
2200 help
2201 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2202 a namespace. A module that makes use of a symbol exported with such a
2203 namespace is required to import the namespace via MODULE_IMPORT_NS().
2204 There is no technical reason to enforce correct namespace imports,
2205 but it creates consistency between symbols defining namespaces and
2206 users importing namespaces they make use of. This option relaxes this
2207 requirement and lifts the enforcement when loading a module.
2208
2209 If unsure, say N.
2210
efd9763d
MY
2211config UNUSED_SYMBOLS
2212 bool "Enable unused/obsolete exported symbols"
2213 default y if X86
2214 help
2215 Unused but exported symbols make the kernel needlessly bigger. For
2216 that reason most of these unused exports will soon be removed. This
2217 option is provided temporarily to provide a transition period in case
2218 some external kernel module needs one of these symbols anyway. If you
2219 encounter such a case in your module, consider if you are actually
2220 using the right API. (rationale: since nobody in the kernel is using
2221 this in a module, there is a pretty good chance it's actually the
2222 wrong interface to use). If you really need the symbol, please send a
2223 mail to the linux kernel mailing list mentioning the symbol and why
2224 you really need it, and what the merge plan to the mainline kernel for
2225 your module is.
2226
dbacb0ef
NP
2227config TRIM_UNUSED_KSYMS
2228 bool "Trim unused exported kernel symbols"
d189c2a4 2229 depends on !UNUSED_SYMBOLS
dbacb0ef
NP
2230 help
2231 The kernel and some modules make many symbols available for
2232 other modules to use via EXPORT_SYMBOL() and variants. Depending
2233 on the set of modules being selected in your kernel configuration,
2234 many of those exported symbols might never be used.
2235
2236 This option allows for unused exported symbols to be dropped from
2237 the build. In turn, this provides the compiler more opportunities
2238 (especially when using LTO) for optimizing the code and reducing
2239 binary size. This might have some security advantages as well.
2240
f1cb637e 2241 If unsure, or if you need to build out-of-tree modules, say N.
dbacb0ef 2242
1518c633
QP
2243config UNUSED_KSYMS_WHITELIST
2244 string "Whitelist of symbols to keep in ksymtab"
2245 depends on TRIM_UNUSED_KSYMS
2246 help
2247 By default, all unused exported symbols will be un-exported from the
2248 build when TRIM_UNUSED_KSYMS is selected.
2249
2250 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2251 exported at all times, even in absence of in-tree users. The value to
2252 set here is the path to a text file containing the list of symbols,
2253 one per line. The path can be absolute, or relative to the kernel
2254 source tree.
2255
0b0de144
RD
2256endif # MODULES
2257
6c9692e2
PZ
2258config MODULES_TREE_LOOKUP
2259 def_bool y
2260 depends on PERF_EVENTS || TRACING
2261
98a79d6a
RR
2262config INIT_ALL_POSSIBLE
2263 bool
2264 help
5f054e31
RR
2265 Back when each arch used to define their own cpu_online_mask and
2266 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
98a79d6a
RR
2267 with all 1s, and others with all 0s. When they were centralised,
2268 it was better to provide this option than to break all the archs
692105b8 2269 and have several arch maintainers pursuing me down dark alleys.
98a79d6a 2270
3a65dfe8 2271source "block/Kconfig"
e98c3202
AK
2272
2273config PREEMPT_NOTIFIERS
2274 bool
e260be67 2275
16295bec
SK
2276config PADATA
2277 depends on SMP
2278 bool
2279
4520c6a4
DH
2280config ASN1
2281 tristate
2282 help
2283 Build a simple ASN.1 grammar compiler that produces a bytecode output
2284 that can be interpreted by the ASN.1 stream decoder and used to
2285 inform it as to what tags are to be expected in a stream and what
2286 functions to call on what tags.
2287
6beb0009 2288source "kernel/Kconfig.locks"
e61938a9 2289
0ebeea8c
DB
2290config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2291 bool
2292
e61938a9
MD
2293config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2294 bool
1bd21c6c
DB
2295
2296# It may be useful for an architecture to override the definitions of the
7303e30e
DB
2297# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2298# and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2299# different calling convention for syscalls. They can also override the
2300# macros for not-implemented syscalls in kernel/sys_ni.c and
2301# kernel/time/posix-stubs.c. All these overrides need to be available in
2302# <asm/syscall_wrapper.h>.
1bd21c6c
DB
2303config ARCH_HAS_SYSCALL_WRAPPER
2304 def_bool n