0001 # SPDX-License-Identifier: GPL-2.0-only
0002 config CC_VERSION_TEXT
0003 string
0004 default "$(CC_VERSION_TEXT)"
0005 help
0006 This is used in unclear ways:
0007
0008 - Re-run Kconfig when the compiler is updated
0009 The 'default' property references the environment variable,
0010 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
0011 When the compiler is updated, Kconfig will be invoked.
0012
0013 - Ensure full rebuild when the compiler is updated
0014 include/linux/compiler-version.h contains this option in the comment
0015 line so fixdep adds include/config/CC_VERSION_TEXT into the
0016 auto-generated dependency. When the compiler is updated, syncconfig
0017 will touch it and then every file will be rebuilt.
0018
0019 config CC_IS_GCC
0020 def_bool $(success,test "$(cc-name)" = GCC)
0021
0022 config GCC_VERSION
0023 int
0024 default $(cc-version) if CC_IS_GCC
0025 default 0
0026
0027 config CC_IS_CLANG
0028 def_bool $(success,test "$(cc-name)" = Clang)
0029
0030 config CLANG_VERSION
0031 int
0032 default $(cc-version) if CC_IS_CLANG
0033 default 0
0034
0035 config AS_IS_GNU
0036 def_bool $(success,test "$(as-name)" = GNU)
0037
0038 config AS_IS_LLVM
0039 def_bool $(success,test "$(as-name)" = LLVM)
0040
0041 config AS_VERSION
0042 int
0043 # Use clang version if this is the integrated assembler
0044 default CLANG_VERSION if AS_IS_LLVM
0045 default $(as-version)
0046
0047 config LD_IS_BFD
0048 def_bool $(success,test "$(ld-name)" = BFD)
0049
0050 config LD_VERSION
0051 int
0052 default $(ld-version) if LD_IS_BFD
0053 default 0
0054
0055 config LD_IS_LLD
0056 def_bool $(success,test "$(ld-name)" = LLD)
0057
0058 config LLD_VERSION
0059 int
0060 default $(ld-version) if LD_IS_LLD
0061 default 0
0062
0063 config CC_CAN_LINK
0064 bool
0065 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
0066 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
0067
0068 config CC_CAN_LINK_STATIC
0069 bool
0070 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
0071 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
0072
0073 config CC_HAS_ASM_GOTO_OUTPUT
0074 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)
0075
0076 config CC_HAS_ASM_GOTO_TIED_OUTPUT
0077 depends on CC_HAS_ASM_GOTO_OUTPUT
0078 # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
0079 def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
0080
0081 config TOOLS_SUPPORT_RELR
0082 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
0083
0084 config CC_HAS_ASM_INLINE
0085 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
0086
0087 config CC_HAS_NO_PROFILE_FN_ATTR
0088 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
0089
0090 config PAHOLE_VERSION
0091 int
0092 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
0093
0094 config CONSTRUCTORS
0095 bool
0096
0097 config IRQ_WORK
0098 bool
0099
0100 config BUILDTIME_TABLE_SORT
0101 bool
0102
0103 config THREAD_INFO_IN_TASK
0104 bool
0105 help
0106 Select this to move thread_info off the stack into task_struct. To
0107 make this work, an arch will need to remove all thread_info fields
0108 except flags and fix any runtime bugs.
0109
0110 One subtle change that will be needed is to use try_get_task_stack()
0111 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
0112
0113 menu "General setup"
0114
0115 config BROKEN
0116 bool
0117
0118 config BROKEN_ON_SMP
0119 bool
0120 depends on BROKEN || !SMP
0121 default y
0122
0123 config INIT_ENV_ARG_LIMIT
0124 int
0125 default 32 if !UML
0126 default 128 if UML
0127 help
0128 Maximum of each of the number of arguments and environment
0129 variables passed to init from the kernel command line.
0130
0131 config COMPILE_TEST
0132 bool "Compile also drivers which will not load"
0133 depends on HAS_IOMEM
0134 help
0135 Some drivers can be compiled on a different platform than they are
0136 intended to be run on. Despite they cannot be loaded there (or even
0137 when they load they cannot be used due to missing HW support),
0138 developers still, opposing to distributors, might want to build such
0139 drivers to compile-test them.
0140
0141 If you are a developer and want to build everything available, say Y
0142 here. If you are a user/distributor, say N here to exclude useless
0143 drivers to be distributed.
0144
0145 config WERROR
0146 bool "Compile the kernel with warnings as errors"
0147 default COMPILE_TEST
0148 help
0149 A kernel build should not cause any compiler warnings, and this
0150 enables the '-Werror' flag to enforce that rule by default.
0151
0152 However, if you have a new (or very old) compiler with odd and
0153 unusual warnings, or you have some architecture with problems,
0154 you may need to disable this config option in order to
0155 successfully build the kernel.
0156
0157 If in doubt, say Y.
0158
0159 config UAPI_HEADER_TEST
0160 bool "Compile test UAPI headers"
0161 depends on HEADERS_INSTALL && CC_CAN_LINK
0162 help
0163 Compile test headers exported to user-space to ensure they are
0164 self-contained, i.e. compilable as standalone units.
0165
0166 If you are a developer or tester and want to ensure the exported
0167 headers are self-contained, say Y here. Otherwise, choose N.
0168
0169 config LOCALVERSION
0170 string "Local version - append to kernel release"
0171 help
0172 Append an extra string to the end of your kernel version.
0173 This will show up when you type uname, for example.
0174 The string you set here will be appended after the contents of
0175 any files with a filename matching localversion* in your
0176 object and source tree, in that order. Your total string can
0177 be a maximum of 64 characters.
0178
0179 config LOCALVERSION_AUTO
0180 bool "Automatically append version information to the version string"
0181 default y
0182 depends on !COMPILE_TEST
0183 help
0184 This will try to automatically determine if the current tree is a
0185 release tree by looking for git tags that belong to the current
0186 top of tree revision.
0187
0188 A string of the format -gxxxxxxxx will be added to the localversion
0189 if a git-based tree is found. The string generated by this will be
0190 appended after any matching localversion* files, and after the value
0191 set in CONFIG_LOCALVERSION.
0192
0193 (The actual string used here is the first eight characters produced
0194 by running the command:
0195
0196 $ git rev-parse --verify HEAD
0197
0198 which is done within the script "scripts/setlocalversion".)
0199
0200 config BUILD_SALT
0201 string "Build ID Salt"
0202 default ""
0203 help
0204 The build ID is used to link binaries and their debug info. Setting
0205 this option will use the value in the calculation of the build id.
0206 This is mostly useful for distributions which want to ensure the
0207 build is unique between builds. It's safe to leave the default.
0208
0209 config HAVE_KERNEL_GZIP
0210 bool
0211
0212 config HAVE_KERNEL_BZIP2
0213 bool
0214
0215 config HAVE_KERNEL_LZMA
0216 bool
0217
0218 config HAVE_KERNEL_XZ
0219 bool
0220
0221 config HAVE_KERNEL_LZO
0222 bool
0223
0224 config HAVE_KERNEL_LZ4
0225 bool
0226
0227 config HAVE_KERNEL_ZSTD
0228 bool
0229
0230 config HAVE_KERNEL_UNCOMPRESSED
0231 bool
0232
0233 choice
0234 prompt "Kernel compression mode"
0235 default KERNEL_GZIP
0236 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED
0237 help
0238 The linux kernel is a kind of self-extracting executable.
0239 Several compression algorithms are available, which differ
0240 in efficiency, compression and decompression speed.
0241 Compression speed is only relevant when building a kernel.
0242 Decompression speed is relevant at each boot.
0243
0244 If you have any problems with bzip2 or lzma compressed
0245 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
0246 version of this functionality (bzip2 only), for 2.4, was
0247 supplied by Christian Ludwig)
0248
0249 High compression options are mostly useful for users, who
0250 are low on disk space (embedded systems), but for whom ram
0251 size matters less.
0252
0253 If in doubt, select 'gzip'
0254
0255 config KERNEL_GZIP
0256 bool "Gzip"
0257 depends on HAVE_KERNEL_GZIP
0258 help
0259 The old and tried gzip compression. It provides a good balance
0260 between compression ratio and decompression speed.
0261
0262 config KERNEL_BZIP2
0263 bool "Bzip2"
0264 depends on HAVE_KERNEL_BZIP2
0265 help
0266 Its compression ratio and speed is intermediate.
0267 Decompression speed is slowest among the choices. The kernel
0268 size is about 10% smaller with bzip2, in comparison to gzip.
0269 Bzip2 uses a large amount of memory. For modern kernels you
0270 will need at least 8MB RAM or more for booting.
0271
0272 config KERNEL_LZMA
0273 bool "LZMA"
0274 depends on HAVE_KERNEL_LZMA
0275 help
0276 This compression algorithm's ratio is best. Decompression speed
0277 is between gzip and bzip2. Compression is slowest.
0278 The kernel size is about 33% smaller with LZMA in comparison to gzip.
0279
0280 config KERNEL_XZ
0281 bool "XZ"
0282 depends on HAVE_KERNEL_XZ
0283 help
0284 XZ uses the LZMA2 algorithm and instruction set specific
0285 BCJ filters which can improve compression ratio of executable
0286 code. The size of the kernel is about 30% smaller with XZ in
0287 comparison to gzip. On architectures for which there is a BCJ
0288 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
0289 will create a few percent smaller kernel than plain LZMA.
0290
0291 The speed is about the same as with LZMA: The decompression
0292 speed of XZ is better than that of bzip2 but worse than gzip
0293 and LZO. Compression is slow.
0294
0295 config KERNEL_LZO
0296 bool "LZO"
0297 depends on HAVE_KERNEL_LZO
0298 help
0299 Its compression ratio is the poorest among the choices. The kernel
0300 size is about 10% bigger than gzip; however its speed
0301 (both compression and decompression) is the fastest.
0302
0303 config KERNEL_LZ4
0304 bool "LZ4"
0305 depends on HAVE_KERNEL_LZ4
0306 help
0307 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
0308 A preliminary version of LZ4 de/compression tool is available at
0309 <https://code.google.com/p/lz4/>.
0310
0311 Its compression ratio is worse than LZO. The size of the kernel
0312 is about 8% bigger than LZO. But the decompression speed is
0313 faster than LZO.
0314
0315 config KERNEL_ZSTD
0316 bool "ZSTD"
0317 depends on HAVE_KERNEL_ZSTD
0318 help
0319 ZSTD is a compression algorithm targeting intermediate compression
0320 with fast decompression speed. It will compress better than GZIP and
0321 decompress around the same speed as LZO, but slower than LZ4. You
0322 will need at least 192 KB RAM or more for booting. The zstd command
0323 line tool is required for compression.
0324
0325 config KERNEL_UNCOMPRESSED
0326 bool "None"
0327 depends on HAVE_KERNEL_UNCOMPRESSED
0328 help
0329 Produce uncompressed kernel image. This option is usually not what
0330 you want. It is useful for debugging the kernel in slow simulation
0331 environments, where decompressing and moving the kernel is awfully
0332 slow. This option allows early boot code to skip the decompressor
0333 and jump right at uncompressed kernel image.
0334
0335 endchoice
0336
0337 config DEFAULT_INIT
0338 string "Default init path"
0339 default ""
0340 help
0341 This option determines the default init for the system if no init=
0342 option is passed on the kernel command line. If the requested path is
0343 not present, we will still then move on to attempting further
0344 locations (e.g. /sbin/init, etc). If this is empty, we will just use
0345 the fallback list when init= is not passed.
0346
0347 config DEFAULT_HOSTNAME
0348 string "Default hostname"
0349 default "(none)"
0350 help
0351 This option determines the default system hostname before userspace
0352 calls sethostname(2). The kernel traditionally uses "(none)" here,
0353 but you may wish to use a different default here to make a minimal
0354 system more usable with less configuration.
0355
0356 config SYSVIPC
0357 bool "System V IPC"
0358 help
0359 Inter Process Communication is a suite of library functions and
0360 system calls which let processes (running programs) synchronize and
0361 exchange information. It is generally considered to be a good thing,
0362 and some programs won't run unless you say Y here. In particular, if
0363 you want to run the DOS emulator dosemu under Linux (read the
0364 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
0365 you'll need to say Y here.
0366
0367 You can find documentation about IPC with "info ipc" and also in
0368 section 6.4 of the Linux Programmer's Guide, available from
0369 <http://www.tldp.org/guides.html>.
0370
0371 config SYSVIPC_SYSCTL
0372 bool
0373 depends on SYSVIPC
0374 depends on SYSCTL
0375 default y
0376
0377 config SYSVIPC_COMPAT
0378 def_bool y
0379 depends on COMPAT && SYSVIPC
0380
0381 config POSIX_MQUEUE
0382 bool "POSIX Message Queues"
0383 depends on NET
0384 help
0385 POSIX variant of message queues is a part of IPC. In POSIX message
0386 queues every message has a priority which decides about succession
0387 of receiving it by a process. If you want to compile and run
0388 programs written e.g. for Solaris with use of its POSIX message
0389 queues (functions mq_*) say Y here.
0390
0391 POSIX message queues are visible as a filesystem called 'mqueue'
0392 and can be mounted somewhere if you want to do filesystem
0393 operations on message queues.
0394
0395 If unsure, say Y.
0396
0397 config POSIX_MQUEUE_SYSCTL
0398 bool
0399 depends on POSIX_MQUEUE
0400 depends on SYSCTL
0401 default y
0402
0403 config WATCH_QUEUE
0404 bool "General notification queue"
0405 default n
0406 help
0407
0408 This is a general notification queue for the kernel to pass events to
0409 userspace by splicing them into pipes. It can be used in conjunction
0410 with watches for key/keyring change notifications and device
0411 notifications.
0412
0413 See Documentation/core-api/watch_queue.rst
0414
0415 config CROSS_MEMORY_ATTACH
0416 bool "Enable process_vm_readv/writev syscalls"
0417 depends on MMU
0418 default y
0419 help
0420 Enabling this option adds the system calls process_vm_readv and
0421 process_vm_writev which allow a process with the correct privileges
0422 to directly read from or write to another process' address space.
0423 See the man page for more details.
0424
0425 config USELIB
0426 bool "uselib syscall (for libc5 and earlier)"
0427 default ALPHA || M68K || SPARC
0428 help
0429 This option enables the uselib syscall, a system call used in the
0430 dynamic linker from libc5 and earlier. glibc does not use this
0431 system call. If you intend to run programs built on libc5 or
0432 earlier, you may need to enable this syscall. Current systems
0433 running glibc can safely disable this.
0434
0435 config AUDIT
0436 bool "Auditing support"
0437 depends on NET
0438 help
0439 Enable auditing infrastructure that can be used with another
0440 kernel subsystem, such as SELinux (which requires this for
0441 logging of avc messages output). System call auditing is included
0442 on architectures which support it.
0443
0444 config HAVE_ARCH_AUDITSYSCALL
0445 bool
0446
0447 config AUDITSYSCALL
0448 def_bool y
0449 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
0450 select FSNOTIFY
0451
0452 source "kernel/irq/Kconfig"
0453 source "kernel/time/Kconfig"
0454 source "kernel/bpf/Kconfig"
0455 source "kernel/Kconfig.preempt"
0456
0457 menu "CPU/Task time and stats accounting"
0458
0459 config VIRT_CPU_ACCOUNTING
0460 bool
0461
0462 choice
0463 prompt "Cputime accounting"
0464 default TICK_CPU_ACCOUNTING if !PPC64
0465 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
0466
0467 # Kind of a stub config for the pure tick based cputime accounting
0468 config TICK_CPU_ACCOUNTING
0469 bool "Simple tick based cputime accounting"
0470 depends on !S390 && !NO_HZ_FULL
0471 help
0472 This is the basic tick based cputime accounting that maintains
0473 statistics about user, system and idle time spent on per jiffies
0474 granularity.
0475
0476 If unsure, say Y.
0477
0478 config VIRT_CPU_ACCOUNTING_NATIVE
0479 bool "Deterministic task and CPU time accounting"
0480 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
0481 select VIRT_CPU_ACCOUNTING
0482 help
0483 Select this option to enable more accurate task and CPU time
0484 accounting. This is done by reading a CPU counter on each
0485 kernel entry and exit and on transitions within the kernel
0486 between system, softirq and hardirq state, so there is a
0487 small performance impact. In the case of s390 or IBM POWER > 5,
0488 this also enables accounting of stolen time on logically-partitioned
0489 systems.
0490
0491 config VIRT_CPU_ACCOUNTING_GEN
0492 bool "Full dynticks CPU time accounting"
0493 depends on HAVE_CONTEXT_TRACKING_USER
0494 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
0495 depends on GENERIC_CLOCKEVENTS
0496 select VIRT_CPU_ACCOUNTING
0497 select CONTEXT_TRACKING_USER
0498 help
0499 Select this option to enable task and CPU time accounting on full
0500 dynticks systems. This accounting is implemented by watching every
0501 kernel-user boundaries using the context tracking subsystem.
0502 The accounting is thus performed at the expense of some significant
0503 overhead.
0504
0505 For now this is only useful if you are working on the full
0506 dynticks subsystem development.
0507
0508 If unsure, say N.
0509
0510 endchoice
0511
0512 config IRQ_TIME_ACCOUNTING
0513 bool "Fine granularity task level IRQ time accounting"
0514 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
0515 help
0516 Select this option to enable fine granularity task irq time
0517 accounting. This is done by reading a timestamp on each
0518 transitions between softirq and hardirq state, so there can be a
0519 small performance impact.
0520
0521 If in doubt, say N here.
0522
0523 config HAVE_SCHED_AVG_IRQ
0524 def_bool y
0525 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
0526 depends on SMP
0527
0528 config SCHED_THERMAL_PRESSURE
0529 bool
0530 default y if ARM && ARM_CPU_TOPOLOGY
0531 default y if ARM64
0532 depends on SMP
0533 depends on CPU_FREQ_THERMAL
0534 help
0535 Select this option to enable thermal pressure accounting in the
0536 scheduler. Thermal pressure is the value conveyed to the scheduler
0537 that reflects the reduction in CPU compute capacity resulted from
0538 thermal throttling. Thermal throttling occurs when the performance of
0539 a CPU is capped due to high operating temperatures.
0540
0541 If selected, the scheduler will be able to balance tasks accordingly,
0542 i.e. put less load on throttled CPUs than on non/less throttled ones.
0543
0544 This requires the architecture to implement
0545 arch_update_thermal_pressure() and arch_scale_thermal_pressure().
0546
0547 config BSD_PROCESS_ACCT
0548 bool "BSD Process Accounting"
0549 depends on MULTIUSER
0550 help
0551 If you say Y here, a user level program will be able to instruct the
0552 kernel (via a special system call) to write process accounting
0553 information to a file: whenever a process exits, information about
0554 that process will be appended to the file by the kernel. The
0555 information includes things such as creation time, owning user,
0556 command name, memory usage, controlling terminal etc. (the complete
0557 list is in the struct acct in <file:include/linux/acct.h>). It is
0558 up to the user level program to do useful things with this
0559 information. This is generally a good idea, so say Y.
0560
0561 config BSD_PROCESS_ACCT_V3
0562 bool "BSD Process Accounting version 3 file format"
0563 depends on BSD_PROCESS_ACCT
0564 default n
0565 help
0566 If you say Y here, the process accounting information is written
0567 in a new file format that also logs the process IDs of each
0568 process and its parent. Note that this file format is incompatible
0569 with previous v0/v1/v2 file formats, so you will need updated tools
0570 for processing it. A preliminary version of these tools is available
0571 at <http://www.gnu.org/software/acct/>.
0572
0573 config TASKSTATS
0574 bool "Export task/process statistics through netlink"
0575 depends on NET
0576 depends on MULTIUSER
0577 default n
0578 help
0579 Export selected statistics for tasks/processes through the
0580 generic netlink interface. Unlike BSD process accounting, the
0581 statistics are available during the lifetime of tasks/processes as
0582 responses to commands. Like BSD accounting, they are sent to user
0583 space on task exit.
0584
0585 Say N if unsure.
0586
0587 config TASK_DELAY_ACCT
0588 bool "Enable per-task delay accounting"
0589 depends on TASKSTATS
0590 select SCHED_INFO
0591 help
0592 Collect information on time spent by a task waiting for system
0593 resources like cpu, synchronous block I/O completion and swapping
0594 in pages. Such statistics can help in setting a task's priorities
0595 relative to other tasks for cpu, io, rss limits etc.
0596
0597 Say N if unsure.
0598
0599 config TASK_XACCT
0600 bool "Enable extended accounting over taskstats"
0601 depends on TASKSTATS
0602 help
0603 Collect extended task accounting data and send the data
0604 to userland for processing over the taskstats interface.
0605
0606 Say N if unsure.
0607
0608 config TASK_IO_ACCOUNTING
0609 bool "Enable per-task storage I/O accounting"
0610 depends on TASK_XACCT
0611 help
0612 Collect information on the number of bytes of storage I/O which this
0613 task has caused.
0614
0615 Say N if unsure.
0616
0617 config PSI
0618 bool "Pressure stall information tracking"
0619 help
0620 Collect metrics that indicate how overcommitted the CPU, memory,
0621 and IO capacity are in the system.
0622
0623 If you say Y here, the kernel will create /proc/pressure/ with the
0624 pressure statistics files cpu, memory, and io. These will indicate
0625 the share of walltime in which some or all tasks in the system are
0626 delayed due to contention of the respective resource.
0627
0628 In kernels with cgroup support, cgroups (cgroup2 only) will
0629 have cpu.pressure, memory.pressure, and io.pressure files,
0630 which aggregate pressure stalls for the grouped tasks only.
0631
0632 For more details see Documentation/accounting/psi.rst.
0633
0634 Say N if unsure.
0635
0636 config PSI_DEFAULT_DISABLED
0637 bool "Require boot parameter to enable pressure stall information tracking"
0638 default n
0639 depends on PSI
0640 help
0641 If set, pressure stall information tracking will be disabled
0642 per default but can be enabled through passing psi=1 on the
0643 kernel commandline during boot.
0644
0645 This feature adds some code to the task wakeup and sleep
0646 paths of the scheduler. The overhead is too low to affect
0647 common scheduling-intense workloads in practice (such as
0648 webservers, memcache), but it does show up in artificial
0649 scheduler stress tests, such as hackbench.
0650
0651 If you are paranoid and not sure what the kernel will be
0652 used for, say Y.
0653
0654 Say N if unsure.
0655
0656 endmenu # "CPU/Task time and stats accounting"
0657
0658 config CPU_ISOLATION
0659 bool "CPU isolation"
0660 depends on SMP || COMPILE_TEST
0661 default y
0662 help
0663 Make sure that CPUs running critical tasks are not disturbed by
0664 any source of "noise" such as unbound workqueues, timers, kthreads...
0665 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
0666 the "isolcpus=" boot parameter.
0667
0668 Say Y if unsure.
0669
0670 source "kernel/rcu/Kconfig"
0671
0672 config BUILD_BIN2C
0673 bool
0674 default n
0675
0676 config IKCONFIG
0677 tristate "Kernel .config support"
0678 help
0679 This option enables the complete Linux kernel ".config" file
0680 contents to be saved in the kernel. It provides documentation
0681 of which kernel options are used in a running kernel or in an
0682 on-disk kernel. This information can be extracted from the kernel
0683 image file with the script scripts/extract-ikconfig and used as
0684 input to rebuild the current kernel or to build another kernel.
0685 It can also be extracted from a running kernel by reading
0686 /proc/config.gz if enabled (below).
0687
0688 config IKCONFIG_PROC
0689 bool "Enable access to .config through /proc/config.gz"
0690 depends on IKCONFIG && PROC_FS
0691 help
0692 This option enables access to the kernel configuration file
0693 through /proc/config.gz.
0694
0695 config IKHEADERS
0696 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
0697 depends on SYSFS
0698 help
0699 This option enables access to the in-kernel headers that are generated during
0700 the build process. These can be used to build eBPF tracing programs,
0701 or similar programs. If you build the headers as a module, a module called
0702 kheaders.ko is built which can be loaded on-demand to get access to headers.
0703
0704 config LOG_BUF_SHIFT
0705 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
0706 range 12 25
0707 default 17
0708 depends on PRINTK
0709 help
0710 Select the minimal kernel log buffer size as a power of 2.
0711 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
0712 parameter, see below. Any higher size also might be forced
0713 by "log_buf_len" boot parameter.
0714
0715 Examples:
0716 17 => 128 KB
0717 16 => 64 KB
0718 15 => 32 KB
0719 14 => 16 KB
0720 13 => 8 KB
0721 12 => 4 KB
0722
0723 config LOG_CPU_MAX_BUF_SHIFT
0724 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
0725 depends on SMP
0726 range 0 21
0727 default 12 if !BASE_SMALL
0728 default 0 if BASE_SMALL
0729 depends on PRINTK
0730 help
0731 This option allows to increase the default ring buffer size
0732 according to the number of CPUs. The value defines the contribution
0733 of each CPU as a power of 2. The used space is typically only few
0734 lines however it might be much more when problems are reported,
0735 e.g. backtraces.
0736
0737 The increased size means that a new buffer has to be allocated and
0738 the original static one is unused. It makes sense only on systems
0739 with more CPUs. Therefore this value is used only when the sum of
0740 contributions is greater than the half of the default kernel ring
0741 buffer as defined by LOG_BUF_SHIFT. The default values are set
0742 so that more than 16 CPUs are needed to trigger the allocation.
0743
0744 Also this option is ignored when "log_buf_len" kernel parameter is
0745 used as it forces an exact (power of two) size of the ring buffer.
0746
0747 The number of possible CPUs is used for this computation ignoring
0748 hotplugging making the computation optimal for the worst case
0749 scenario while allowing a simple algorithm to be used from bootup.
0750
0751 Examples shift values and their meaning:
0752 17 => 128 KB for each CPU
0753 16 => 64 KB for each CPU
0754 15 => 32 KB for each CPU
0755 14 => 16 KB for each CPU
0756 13 => 8 KB for each CPU
0757 12 => 4 KB for each CPU
0758
0759 config PRINTK_SAFE_LOG_BUF_SHIFT
0760 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
0761 range 10 21
0762 default 13
0763 depends on PRINTK
0764 help
0765 Select the size of an alternate printk per-CPU buffer where messages
0766 printed from usafe contexts are temporary stored. One example would
0767 be NMI messages, another one - printk recursion. The messages are
0768 copied to the main log buffer in a safe context to avoid a deadlock.
0769 The value defines the size as a power of 2.
0770
0771 Those messages are rare and limited. The largest one is when
0772 a backtrace is printed. It usually fits into 4KB. Select
0773 8KB if you want to be on the safe side.
0774
0775 Examples:
0776 17 => 128 KB for each CPU
0777 16 => 64 KB for each CPU
0778 15 => 32 KB for each CPU
0779 14 => 16 KB for each CPU
0780 13 => 8 KB for each CPU
0781 12 => 4 KB for each CPU
0782
0783 config PRINTK_INDEX
0784 bool "Printk indexing debugfs interface"
0785 depends on PRINTK && DEBUG_FS
0786 help
0787 Add support for indexing of all printk formats known at compile time
0788 at <debugfs>/printk/index/<module>.
0789
0790 This can be used as part of maintaining daemons which monitor
0791 /dev/kmsg, as it permits auditing the printk formats present in a
0792 kernel, allowing detection of cases where monitored printks are
0793 changed or no longer present.
0794
0795 There is no additional runtime cost to printk with this enabled.
0796
0797 #
0798 # Architectures with an unreliable sched_clock() should select this:
0799 #
0800 config HAVE_UNSTABLE_SCHED_CLOCK
0801 bool
0802
0803 config GENERIC_SCHED_CLOCK
0804 bool
0805
0806 menu "Scheduler features"
0807
0808 config UCLAMP_TASK
0809 bool "Enable utilization clamping for RT/FAIR tasks"
0810 depends on CPU_FREQ_GOV_SCHEDUTIL
0811 help
0812 This feature enables the scheduler to track the clamped utilization
0813 of each CPU based on RUNNABLE tasks scheduled on that CPU.
0814
0815 With this option, the user can specify the min and max CPU
0816 utilization allowed for RUNNABLE tasks. The max utilization defines
0817 the maximum frequency a task should use while the min utilization
0818 defines the minimum frequency it should use.
0819
0820 Both min and max utilization clamp values are hints to the scheduler,
0821 aiming at improving its frequency selection policy, but they do not
0822 enforce or grant any specific bandwidth for tasks.
0823
0824 If in doubt, say N.
0825
0826 config UCLAMP_BUCKETS_COUNT
0827 int "Number of supported utilization clamp buckets"
0828 range 5 20
0829 default 5
0830 depends on UCLAMP_TASK
0831 help
0832 Defines the number of clamp buckets to use. The range of each bucket
0833 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
0834 number of clamp buckets the finer their granularity and the higher
0835 the precision of clamping aggregation and tracking at run-time.
0836
0837 For example, with the minimum configuration value we will have 5
0838 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
0839 be refcounted in the [20..39]% bucket and will set the bucket clamp
0840 effective value to 25%.
0841 If a second 30% boosted task should be co-scheduled on the same CPU,
0842 that task will be refcounted in the same bucket of the first task and
0843 it will boost the bucket clamp effective value to 30%.
0844 The clamp effective value of a bucket is reset to its nominal value
0845 (20% in the example above) when there are no more tasks refcounted in
0846 that bucket.
0847
0848 An additional boost/capping margin can be added to some tasks. In the
0849 example above the 25% task will be boosted to 30% until it exits the
0850 CPU. If that should be considered not acceptable on certain systems,
0851 it's always possible to reduce the margin by increasing the number of
0852 clamp buckets to trade off used memory for run-time tracking
0853 precision.
0854
0855 If in doubt, use the default value.
0856
0857 endmenu
0858
0859 #
0860 # For architectures that want to enable the support for NUMA-affine scheduler
0861 # balancing logic:
0862 #
0863 config ARCH_SUPPORTS_NUMA_BALANCING
0864 bool
0865
0866 #
0867 # For architectures that prefer to flush all TLBs after a number of pages
0868 # are unmapped instead of sending one IPI per page to flush. The architecture
0869 # must provide guarantees on what happens if a clean TLB cache entry is
0870 # written after the unmap. Details are in mm/rmap.c near the check for
0871 # should_defer_flush. The architecture should also consider if the full flush
0872 # and the refill costs are offset by the savings of sending fewer IPIs.
0873 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
0874 bool
0875
0876 config CC_HAS_INT128
0877 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
0878
0879 config CC_IMPLICIT_FALLTHROUGH
0880 string
0881 default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
0882 default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
0883
0884 # Currently, disable gcc-12 array-bounds globally.
0885 # We may want to target only particular configurations some day.
0886 config GCC12_NO_ARRAY_BOUNDS
0887 def_bool y
0888
0889 config CC_NO_ARRAY_BOUNDS
0890 bool
0891 default y if CC_IS_GCC && GCC_VERSION >= 120000 && GCC_VERSION < 130000 && GCC12_NO_ARRAY_BOUNDS
0892
0893 #
0894 # For architectures that know their GCC __int128 support is sound
0895 #
0896 config ARCH_SUPPORTS_INT128
0897 bool
0898
0899 # For architectures that (ab)use NUMA to represent different memory regions
0900 # all cpu-local but of different latencies, such as SuperH.
0901 #
0902 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
0903 bool
0904
0905 config NUMA_BALANCING
0906 bool "Memory placement aware NUMA scheduler"
0907 depends on ARCH_SUPPORTS_NUMA_BALANCING
0908 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
0909 depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
0910 help
0911 This option adds support for automatic NUMA aware memory/task placement.
0912 The mechanism is quite primitive and is based on migrating memory when
0913 it has references to the node the task is running on.
0914
0915 This system will be inactive on UMA systems.
0916
0917 config NUMA_BALANCING_DEFAULT_ENABLED
0918 bool "Automatically enable NUMA aware memory/task placement"
0919 default y
0920 depends on NUMA_BALANCING
0921 help
0922 If set, automatic NUMA balancing will be enabled if running on a NUMA
0923 machine.
0924
0925 menuconfig CGROUPS
0926 bool "Control Group support"
0927 select KERNFS
0928 help
0929 This option adds support for grouping sets of processes together, for
0930 use with process control subsystems such as Cpusets, CFS, memory
0931 controls or device isolation.
0932 See
0933 - Documentation/scheduler/sched-design-CFS.rst (CFS)
0934 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
0935 and resource control)
0936
0937 Say N if unsure.
0938
0939 if CGROUPS
0940
0941 config PAGE_COUNTER
0942 bool
0943
0944 config CGROUP_FAVOR_DYNMODS
0945 bool "Favor dynamic modification latency reduction by default"
0946 help
0947 This option enables the "favordynmods" mount option by default
0948 which reduces the latencies of dynamic cgroup modifications such
0949 as task migrations and controller on/offs at the cost of making
0950 hot path operations such as forks and exits more expensive.
0951
0952 Say N if unsure.
0953
0954 config MEMCG
0955 bool "Memory controller"
0956 select PAGE_COUNTER
0957 select EVENTFD
0958 help
0959 Provides control over the memory footprint of tasks in a cgroup.
0960
0961 config MEMCG_SWAP
0962 bool
0963 depends on MEMCG && SWAP
0964 default y
0965
0966 config MEMCG_KMEM
0967 bool
0968 depends on MEMCG && !SLOB
0969 default y
0970
0971 config BLK_CGROUP
0972 bool "IO controller"
0973 depends on BLOCK
0974 default n
0975 help
0976 Generic block IO controller cgroup interface. This is the common
0977 cgroup interface which should be used by various IO controlling
0978 policies.
0979
0980 Currently, CFQ IO scheduler uses it to recognize task groups and
0981 control disk bandwidth allocation (proportional time slice allocation)
0982 to such task groups. It is also used by bio throttling logic in
0983 block layer to implement upper limit in IO rates on a device.
0984
0985 This option only enables generic Block IO controller infrastructure.
0986 One needs to also enable actual IO controlling logic/policy. For
0987 enabling proportional weight division of disk bandwidth in CFQ, set
0988 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
0989 CONFIG_BLK_DEV_THROTTLING=y.
0990
0991 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
0992
0993 config CGROUP_WRITEBACK
0994 bool
0995 depends on MEMCG && BLK_CGROUP
0996 default y
0997
0998 menuconfig CGROUP_SCHED
0999 bool "CPU controller"
1000 default n
1001 help
1002 This feature lets CPU scheduler recognize task groups and control CPU
1003 bandwidth allocation to such task groups. It uses cgroups to group
1004 tasks.
1005
1006 if CGROUP_SCHED
1007 config FAIR_GROUP_SCHED
1008 bool "Group scheduling for SCHED_OTHER"
1009 depends on CGROUP_SCHED
1010 default CGROUP_SCHED
1011
1012 config CFS_BANDWIDTH
1013 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1014 depends on FAIR_GROUP_SCHED
1015 default n
1016 help
1017 This option allows users to define CPU bandwidth rates (limits) for
1018 tasks running within the fair group scheduler. Groups with no limit
1019 set are considered to be unconstrained and will run with no
1020 restriction.
1021 See Documentation/scheduler/sched-bwc.rst for more information.
1022
1023 config RT_GROUP_SCHED
1024 bool "Group scheduling for SCHED_RR/FIFO"
1025 depends on CGROUP_SCHED
1026 default n
1027 help
1028 This feature lets you explicitly allocate real CPU bandwidth
1029 to task groups. If enabled, it will also make it impossible to
1030 schedule realtime tasks for non-root users until you allocate
1031 realtime bandwidth for them.
1032 See Documentation/scheduler/sched-rt-group.rst for more information.
1033
1034 endif #CGROUP_SCHED
1035
1036 config UCLAMP_TASK_GROUP
1037 bool "Utilization clamping per group of tasks"
1038 depends on CGROUP_SCHED
1039 depends on UCLAMP_TASK
1040 default n
1041 help
1042 This feature enables the scheduler to track the clamped utilization
1043 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
1044
1045 When this option is enabled, the user can specify a min and max
1046 CPU bandwidth which is allowed for each single task in a group.
1047 The max bandwidth allows to clamp the maximum frequency a task
1048 can use, while the min bandwidth allows to define a minimum
1049 frequency a task will always use.
1050
1051 When task group based utilization clamping is enabled, an eventually
1052 specified task-specific clamp value is constrained by the cgroup
1053 specified clamp value. Both minimum and maximum task clamping cannot
1054 be bigger than the corresponding clamping defined at task group level.
1055
1056 If in doubt, say N.
1057
1058 config CGROUP_PIDS
1059 bool "PIDs controller"
1060 help
1061 Provides enforcement of process number limits in the scope of a
1062 cgroup. Any attempt to fork more processes than is allowed in the
1063 cgroup will fail. PIDs are fundamentally a global resource because it
1064 is fairly trivial to reach PID exhaustion before you reach even a
1065 conservative kmemcg limit. As a result, it is possible to grind a
1066 system to halt without being limited by other cgroup policies. The
1067 PIDs controller is designed to stop this from happening.
1068
1069 It should be noted that organisational operations (such as attaching
1070 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1071 since the PIDs limit only affects a process's ability to fork, not to
1072 attach to a cgroup.
1073
1074 config CGROUP_RDMA
1075 bool "RDMA controller"
1076 help
1077 Provides enforcement of RDMA resources defined by IB stack.
1078 It is fairly easy for consumers to exhaust RDMA resources, which
1079 can result into resource unavailability to other consumers.
1080 RDMA controller is designed to stop this from happening.
1081 Attaching processes with active RDMA resources to the cgroup
1082 hierarchy is allowed even if can cross the hierarchy's limit.
1083
1084 config CGROUP_FREEZER
1085 bool "Freezer controller"
1086 help
1087 Provides a way to freeze and unfreeze all tasks in a
1088 cgroup.
1089
1090 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1091 controller includes important in-kernel memory consumers per default.
1092
1093 If you're using cgroup2, say N.
1094
1095 config CGROUP_HUGETLB
1096 bool "HugeTLB controller"
1097 depends on HUGETLB_PAGE
1098 select PAGE_COUNTER
1099 default n
1100 help
1101 Provides a cgroup controller for HugeTLB pages.
1102 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1103 The limit is enforced during page fault. Since HugeTLB doesn't
1104 support page reclaim, enforcing the limit at page fault time implies
1105 that, the application will get SIGBUS signal if it tries to access
1106 HugeTLB pages beyond its limit. This requires the application to know
1107 beforehand how much HugeTLB pages it would require for its use. The
1108 control group is tracked in the third page lru pointer. This means
1109 that we cannot use the controller with huge page less than 3 pages.
1110
1111 config CPUSETS
1112 bool "Cpuset controller"
1113 depends on SMP
1114 help
1115 This option will let you create and manage CPUSETs which
1116 allow dynamically partitioning a system into sets of CPUs and
1117 Memory Nodes and assigning tasks to run only within those sets.
1118 This is primarily useful on large SMP or NUMA systems.
1119
1120 Say N if unsure.
1121
1122 config PROC_PID_CPUSET
1123 bool "Include legacy /proc/<pid>/cpuset file"
1124 depends on CPUSETS
1125 default y
1126
1127 config CGROUP_DEVICE
1128 bool "Device controller"
1129 help
1130 Provides a cgroup controller implementing whitelists for
1131 devices which a process in the cgroup can mknod or open.
1132
1133 config CGROUP_CPUACCT
1134 bool "Simple CPU accounting controller"
1135 help
1136 Provides a simple controller for monitoring the
1137 total CPU consumed by the tasks in a cgroup.
1138
1139 config CGROUP_PERF
1140 bool "Perf controller"
1141 depends on PERF_EVENTS
1142 help
1143 This option extends the perf per-cpu mode to restrict monitoring
1144 to threads which belong to the cgroup specified and run on the
1145 designated cpu. Or this can be used to have cgroup ID in samples
1146 so that it can monitor performance events among cgroups.
1147
1148 Say N if unsure.
1149
1150 config CGROUP_BPF
1151 bool "Support for eBPF programs attached to cgroups"
1152 depends on BPF_SYSCALL
1153 select SOCK_CGROUP_DATA
1154 help
1155 Allow attaching eBPF programs to a cgroup using the bpf(2)
1156 syscall command BPF_PROG_ATTACH.
1157
1158 In which context these programs are accessed depends on the type
1159 of attachment. For instance, programs that are attached using
1160 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1161 inet sockets.
1162
1163 config CGROUP_MISC
1164 bool "Misc resource controller"
1165 default n
1166 help
1167 Provides a controller for miscellaneous resources on a host.
1168
1169 Miscellaneous scalar resources are the resources on the host system
1170 which cannot be abstracted like the other cgroups. This controller
1171 tracks and limits the miscellaneous resources used by a process
1172 attached to a cgroup hierarchy.
1173
1174 For more information, please check misc cgroup section in
1175 /Documentation/admin-guide/cgroup-v2.rst.
1176
1177 config CGROUP_DEBUG
1178 bool "Debug controller"
1179 default n
1180 depends on DEBUG_KERNEL
1181 help
1182 This option enables a simple controller that exports
1183 debugging information about the cgroups framework. This
1184 controller is for control cgroup debugging only. Its
1185 interfaces are not stable.
1186
1187 Say N.
1188
1189 config SOCK_CGROUP_DATA
1190 bool
1191 default n
1192
1193 endif # CGROUPS
1194
1195 menuconfig NAMESPACES
1196 bool "Namespaces support" if EXPERT
1197 depends on MULTIUSER
1198 default !EXPERT
1199 help
1200 Provides the way to make tasks work with different objects using
1201 the same id. For example same IPC id may refer to different objects
1202 or same user id or pid may refer to different tasks when used in
1203 different namespaces.
1204
1205 if NAMESPACES
1206
1207 config UTS_NS
1208 bool "UTS namespace"
1209 default y
1210 help
1211 In this namespace tasks see different info provided with the
1212 uname() system call
1213
1214 config TIME_NS
1215 bool "TIME namespace"
1216 depends on GENERIC_VDSO_TIME_NS
1217 default y
1218 help
1219 In this namespace boottime and monotonic clocks can be set.
1220 The time will keep going with the same pace.
1221
1222 config IPC_NS
1223 bool "IPC namespace"
1224 depends on (SYSVIPC || POSIX_MQUEUE)
1225 default y
1226 help
1227 In this namespace tasks work with IPC ids which correspond to
1228 different IPC objects in different namespaces.
1229
1230 config USER_NS
1231 bool "User namespace"
1232 default n
1233 help
1234 This allows containers, i.e. vservers, to use user namespaces
1235 to provide different user info for different servers.
1236
1237 When user namespaces are enabled in the kernel it is
1238 recommended that the MEMCG option also be enabled and that
1239 user-space use the memory control groups to limit the amount
1240 of memory a memory unprivileged users can use.
1241
1242 If unsure, say N.
1243
1244 config PID_NS
1245 bool "PID Namespaces"
1246 default y
1247 help
1248 Support process id namespaces. This allows having multiple
1249 processes with the same pid as long as they are in different
1250 pid namespaces. This is a building block of containers.
1251
1252 config NET_NS
1253 bool "Network namespace"
1254 depends on NET
1255 default y
1256 help
1257 Allow user space to create what appear to be multiple instances
1258 of the network stack.
1259
1260 endif # NAMESPACES
1261
1262 config CHECKPOINT_RESTORE
1263 bool "Checkpoint/restore support"
1264 select PROC_CHILDREN
1265 select KCMP
1266 default n
1267 help
1268 Enables additional kernel features in a sake of checkpoint/restore.
1269 In particular it adds auxiliary prctl codes to setup process text,
1270 data and heap segment sizes, and a few additional /proc filesystem
1271 entries.
1272
1273 If unsure, say N here.
1274
1275 config SCHED_AUTOGROUP
1276 bool "Automatic process group scheduling"
1277 select CGROUPS
1278 select CGROUP_SCHED
1279 select FAIR_GROUP_SCHED
1280 help
1281 This option optimizes the scheduler for common desktop workloads by
1282 automatically creating and populating task groups. This separation
1283 of workloads isolates aggressive CPU burners (like build jobs) from
1284 desktop applications. Task group autogeneration is currently based
1285 upon task session.
1286
1287 config SYSFS_DEPRECATED
1288 bool "Enable deprecated sysfs features to support old userspace tools"
1289 depends on SYSFS
1290 default n
1291 help
1292 This option adds code that switches the layout of the "block" class
1293 devices, to not show up in /sys/class/block/, but only in
1294 /sys/block/.
1295
1296 This switch is only active when the sysfs.deprecated=1 boot option is
1297 passed or the SYSFS_DEPRECATED_V2 option is set.
1298
1299 This option allows new kernels to run on old distributions and tools,
1300 which might get confused by /sys/class/block/. Since 2007/2008 all
1301 major distributions and tools handle this just fine.
1302
1303 Recent distributions and userspace tools after 2009/2010 depend on
1304 the existence of /sys/class/block/, and will not work with this
1305 option enabled.
1306
1307 Only if you are using a new kernel on an old distribution, you might
1308 need to say Y here.
1309
1310 config SYSFS_DEPRECATED_V2
1311 bool "Enable deprecated sysfs features by default"
1312 default n
1313 depends on SYSFS
1314 depends on SYSFS_DEPRECATED
1315 help
1316 Enable deprecated sysfs by default.
1317
1318 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1319 option.
1320
1321 Only if you are using a new kernel on an old distribution, you might
1322 need to say Y here. Even then, odds are you would not need it
1323 enabled, you can always pass the boot option if absolutely necessary.
1324
1325 config RELAY
1326 bool "Kernel->user space relay support (formerly relayfs)"
1327 select IRQ_WORK
1328 help
1329 This option enables support for relay interface support in
1330 certain file systems (such as debugfs).
1331 It is designed to provide an efficient mechanism for tools and
1332 facilities to relay large amounts of data from kernel space to
1333 user space.
1334
1335 If unsure, say N.
1336
1337 config BLK_DEV_INITRD
1338 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1339 help
1340 The initial RAM filesystem is a ramfs which is loaded by the
1341 boot loader (loadlin or lilo) and that is mounted as root
1342 before the normal boot procedure. It is typically used to
1343 load modules needed to mount the "real" root file system,
1344 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1345
1346 If RAM disk support (BLK_DEV_RAM) is also included, this
1347 also enables initial RAM disk (initrd) support and adds
1348 15 Kbytes (more on some other architectures) to the kernel size.
1349
1350 If unsure say Y.
1351
1352 if BLK_DEV_INITRD
1353
1354 source "usr/Kconfig"
1355
1356 endif
1357
1358 config BOOT_CONFIG
1359 bool "Boot config support"
1360 select BLK_DEV_INITRD if !BOOT_CONFIG_EMBED
1361 help
1362 Extra boot config allows system admin to pass a config file as
1363 complemental extension of kernel cmdline when booting.
1364 The boot config file must be attached at the end of initramfs
1365 with checksum, size and magic word.
1366 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1367
1368 If unsure, say Y.
1369
1370 config BOOT_CONFIG_EMBED
1371 bool "Embed bootconfig file in the kernel"
1372 depends on BOOT_CONFIG
1373 help
1374 Embed a bootconfig file given by BOOT_CONFIG_EMBED_FILE in the
1375 kernel. Usually, the bootconfig file is loaded with the initrd
1376 image. But if the system doesn't support initrd, this option will
1377 help you by embedding a bootconfig file while building the kernel.
1378
1379 If unsure, say N.
1380
1381 config BOOT_CONFIG_EMBED_FILE
1382 string "Embedded bootconfig file path"
1383 depends on BOOT_CONFIG_EMBED
1384 help
1385 Specify a bootconfig file which will be embedded to the kernel.
1386 This bootconfig will be used if there is no initrd or no other
1387 bootconfig in the initrd.
1388
1389 config INITRAMFS_PRESERVE_MTIME
1390 bool "Preserve cpio archive mtimes in initramfs"
1391 default y
1392 help
1393 Each entry in an initramfs cpio archive carries an mtime value. When
1394 enabled, extracted cpio items take this mtime, with directory mtime
1395 setting deferred until after creation of any child entries.
1396
1397 If unsure, say Y.
1398
1399 choice
1400 prompt "Compiler optimization level"
1401 default CC_OPTIMIZE_FOR_PERFORMANCE
1402
1403 config CC_OPTIMIZE_FOR_PERFORMANCE
1404 bool "Optimize for performance (-O2)"
1405 help
1406 This is the default optimization level for the kernel, building
1407 with the "-O2" compiler flag for best performance and most
1408 helpful compile-time warnings.
1409
1410 config CC_OPTIMIZE_FOR_SIZE
1411 bool "Optimize for size (-Os)"
1412 help
1413 Choosing this option will pass "-Os" to your compiler resulting
1414 in a smaller kernel.
1415
1416 endchoice
1417
1418 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1419 bool
1420 help
1421 This requires that the arch annotates or otherwise protects
1422 its external entry points from being discarded. Linker scripts
1423 must also merge .text.*, .data.*, and .bss.* correctly into
1424 output sections. Care must be taken not to pull in unrelated
1425 sections (e.g., '.text.init'). Typically '.' in section names
1426 is used to distinguish them from label names / C identifiers.
1427
1428 config LD_DEAD_CODE_DATA_ELIMINATION
1429 bool "Dead code and data elimination (EXPERIMENTAL)"
1430 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1431 depends on EXPERT
1432 depends on $(cc-option,-ffunction-sections -fdata-sections)
1433 depends on $(ld-option,--gc-sections)
1434 help
1435 Enable this if you want to do dead code and data elimination with
1436 the linker by compiling with -ffunction-sections -fdata-sections,
1437 and linking with --gc-sections.
1438
1439 This can reduce on disk and in-memory size of the kernel
1440 code and static data, particularly for small configs and
1441 on small systems. This has the possibility of introducing
1442 silently broken kernel if the required annotations are not
1443 present. This option is not well tested yet, so use at your
1444 own risk.
1445
1446 config LD_ORPHAN_WARN
1447 def_bool y
1448 depends on ARCH_WANT_LD_ORPHAN_WARN
1449 depends on $(ld-option,--orphan-handling=warn)
1450
1451 config SYSCTL
1452 bool
1453
1454 config HAVE_UID16
1455 bool
1456
1457 config SYSCTL_EXCEPTION_TRACE
1458 bool
1459 help
1460 Enable support for /proc/sys/debug/exception-trace.
1461
1462 config SYSCTL_ARCH_UNALIGN_NO_WARN
1463 bool
1464 help
1465 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1466 Allows arch to define/use @no_unaligned_warning to possibly warn
1467 about unaligned access emulation going on under the hood.
1468
1469 config SYSCTL_ARCH_UNALIGN_ALLOW
1470 bool
1471 help
1472 Enable support for /proc/sys/kernel/unaligned-trap
1473 Allows arches to define/use @unaligned_enabled to runtime toggle
1474 the unaligned access emulation.
1475 see arch/parisc/kernel/unaligned.c for reference
1476
1477 config HAVE_PCSPKR_PLATFORM
1478 bool
1479
1480 # interpreter that classic socket filters depend on
1481 config BPF
1482 bool
1483 select CRYPTO_LIB_SHA1
1484
1485 menuconfig EXPERT
1486 bool "Configure standard kernel features (expert users)"
1487 # Unhide debug options, to make the on-by-default options visible
1488 select DEBUG_KERNEL
1489 help
1490 This option allows certain base kernel options and settings
1491 to be disabled or tweaked. This is for specialized
1492 environments which can tolerate a "non-standard" kernel.
1493 Only use this if you really know what you are doing.
1494
1495 config UID16
1496 bool "Enable 16-bit UID system calls" if EXPERT
1497 depends on HAVE_UID16 && MULTIUSER
1498 default y
1499 help
1500 This enables the legacy 16-bit UID syscall wrappers.
1501
1502 config MULTIUSER
1503 bool "Multiple users, groups and capabilities support" if EXPERT
1504 default y
1505 help
1506 This option enables support for non-root users, groups and
1507 capabilities.
1508
1509 If you say N here, all processes will run with UID 0, GID 0, and all
1510 possible capabilities. Saying N here also compiles out support for
1511 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1512 setgid, and capset.
1513
1514 If unsure, say Y here.
1515
1516 config SGETMASK_SYSCALL
1517 bool "sgetmask/ssetmask syscalls support" if EXPERT
1518 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1519 help
1520 sys_sgetmask and sys_ssetmask are obsolete system calls
1521 no longer supported in libc but still enabled by default in some
1522 architectures.
1523
1524 If unsure, leave the default option here.
1525
1526 config SYSFS_SYSCALL
1527 bool "Sysfs syscall support" if EXPERT
1528 default y
1529 help
1530 sys_sysfs is an obsolete system call no longer supported in libc.
1531 Note that disabling this option is more secure but might break
1532 compatibility with some systems.
1533
1534 If unsure say Y here.
1535
1536 config FHANDLE
1537 bool "open by fhandle syscalls" if EXPERT
1538 select EXPORTFS
1539 default y
1540 help
1541 If you say Y here, a user level program will be able to map
1542 file names to handle and then later use the handle for
1543 different file system operations. This is useful in implementing
1544 userspace file servers, which now track files using handles instead
1545 of names. The handle would remain the same even if file names
1546 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1547 syscalls.
1548
1549 config POSIX_TIMERS
1550 bool "Posix Clocks & timers" if EXPERT
1551 default y
1552 help
1553 This includes native support for POSIX timers to the kernel.
1554 Some embedded systems have no use for them and therefore they
1555 can be configured out to reduce the size of the kernel image.
1556
1557 When this option is disabled, the following syscalls won't be
1558 available: timer_create, timer_gettime: timer_getoverrun,
1559 timer_settime, timer_delete, clock_adjtime, getitimer,
1560 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1561 clock_getres and clock_nanosleep syscalls will be limited to
1562 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1563
1564 If unsure say y.
1565
1566 config PRINTK
1567 default y
1568 bool "Enable support for printk" if EXPERT
1569 select IRQ_WORK
1570 help
1571 This option enables normal printk support. Removing it
1572 eliminates most of the message strings from the kernel image
1573 and makes the kernel more or less silent. As this makes it
1574 very difficult to diagnose system problems, saying N here is
1575 strongly discouraged.
1576
1577 config BUG
1578 bool "BUG() support" if EXPERT
1579 default y
1580 help
1581 Disabling this option eliminates support for BUG and WARN, reducing
1582 the size of your kernel image and potentially quietly ignoring
1583 numerous fatal conditions. You should only consider disabling this
1584 option for embedded systems with no facilities for reporting errors.
1585 Just say Y.
1586
1587 config ELF_CORE
1588 depends on COREDUMP
1589 default y
1590 bool "Enable ELF core dumps" if EXPERT
1591 help
1592 Enable support for generating core dumps. Disabling saves about 4k.
1593
1594
1595 config PCSPKR_PLATFORM
1596 bool "Enable PC-Speaker support" if EXPERT
1597 depends on HAVE_PCSPKR_PLATFORM
1598 select I8253_LOCK
1599 default y
1600 help
1601 This option allows to disable the internal PC-Speaker
1602 support, saving some memory.
1603
1604 config BASE_FULL
1605 default y
1606 bool "Enable full-sized data structures for core" if EXPERT
1607 help
1608 Disabling this option reduces the size of miscellaneous core
1609 kernel data structures. This saves memory on small machines,
1610 but may reduce performance.
1611
1612 config FUTEX
1613 bool "Enable futex support" if EXPERT
1614 depends on !(SPARC32 && SMP)
1615 default y
1616 imply RT_MUTEXES
1617 help
1618 Disabling this option will cause the kernel to be built without
1619 support for "fast userspace mutexes". The resulting kernel may not
1620 run glibc-based applications correctly.
1621
1622 config FUTEX_PI
1623 bool
1624 depends on FUTEX && RT_MUTEXES
1625 default y
1626
1627 config EPOLL
1628 bool "Enable eventpoll support" if EXPERT
1629 default y
1630 help
1631 Disabling this option will cause the kernel to be built without
1632 support for epoll family of system calls.
1633
1634 config SIGNALFD
1635 bool "Enable signalfd() system call" if EXPERT
1636 default y
1637 help
1638 Enable the signalfd() system call that allows to receive signals
1639 on a file descriptor.
1640
1641 If unsure, say Y.
1642
1643 config TIMERFD
1644 bool "Enable timerfd() system call" if EXPERT
1645 default y
1646 help
1647 Enable the timerfd() system call that allows to receive timer
1648 events on a file descriptor.
1649
1650 If unsure, say Y.
1651
1652 config EVENTFD
1653 bool "Enable eventfd() system call" if EXPERT
1654 default y
1655 help
1656 Enable the eventfd() system call that allows to receive both
1657 kernel notification (ie. KAIO) or userspace notifications.
1658
1659 If unsure, say Y.
1660
1661 config SHMEM
1662 bool "Use full shmem filesystem" if EXPERT
1663 default y
1664 depends on MMU
1665 help
1666 The shmem is an internal filesystem used to manage shared memory.
1667 It is backed by swap and manages resource limits. It is also exported
1668 to userspace as tmpfs if TMPFS is enabled. Disabling this
1669 option replaces shmem and tmpfs with the much simpler ramfs code,
1670 which may be appropriate on small systems without swap.
1671
1672 config AIO
1673 bool "Enable AIO support" if EXPERT
1674 default y
1675 help
1676 This option enables POSIX asynchronous I/O which may by used
1677 by some high performance threaded applications. Disabling
1678 this option saves about 7k.
1679
1680 config IO_URING
1681 bool "Enable IO uring support" if EXPERT
1682 select IO_WQ
1683 default y
1684 help
1685 This option enables support for the io_uring interface, enabling
1686 applications to submit and complete IO through submission and
1687 completion rings that are shared between the kernel and application.
1688
1689 config ADVISE_SYSCALLS
1690 bool "Enable madvise/fadvise syscalls" if EXPERT
1691 default y
1692 help
1693 This option enables the madvise and fadvise syscalls, used by
1694 applications to advise the kernel about their future memory or file
1695 usage, improving performance. If building an embedded system where no
1696 applications use these syscalls, you can disable this option to save
1697 space.
1698
1699 config MEMBARRIER
1700 bool "Enable membarrier() system call" if EXPERT
1701 default y
1702 help
1703 Enable the membarrier() system call that allows issuing memory
1704 barriers across all running threads, which can be used to distribute
1705 the cost of user-space memory barriers asymmetrically by transforming
1706 pairs of memory barriers into pairs consisting of membarrier() and a
1707 compiler barrier.
1708
1709 If unsure, say Y.
1710
1711 config KALLSYMS
1712 bool "Load all symbols for debugging/ksymoops" if EXPERT
1713 default y
1714 help
1715 Say Y here to let the kernel print out symbolic crash information and
1716 symbolic stack backtraces. This increases the size of the kernel
1717 somewhat, as all symbols have to be loaded into the kernel image.
1718
1719 config KALLSYMS_ALL
1720 bool "Include all symbols in kallsyms"
1721 depends on DEBUG_KERNEL && KALLSYMS
1722 help
1723 Normally kallsyms only contains the symbols of functions for nicer
1724 OOPS messages and backtraces (i.e., symbols from the text and inittext
1725 sections). This is sufficient for most cases. And only if you want to
1726 enable kernel live patching, or other less common use cases (e.g.,
1727 when a debugger is used) all symbols are required (i.e., names of
1728 variables from the data sections, etc).
1729
1730 This option makes sure that all symbols are loaded into the kernel
1731 image (i.e., symbols from all sections) in cost of increased kernel
1732 size (depending on the kernel configuration, it may be 300KiB or
1733 something like this).
1734
1735 Say N unless you really need all symbols, or kernel live patching.
1736
1737 config KALLSYMS_ABSOLUTE_PERCPU
1738 bool
1739 depends on KALLSYMS
1740 default X86_64 && SMP
1741
1742 config KALLSYMS_BASE_RELATIVE
1743 bool
1744 depends on KALLSYMS
1745 default !IA64
1746 help
1747 Instead of emitting them as absolute values in the native word size,
1748 emit the symbol references in the kallsyms table as 32-bit entries,
1749 each containing a relative value in the range [base, base + U32_MAX]
1750 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1751 an absolute value in the range [0, S32_MAX] or a relative value in the
1752 range [base, base + S32_MAX], where base is the lowest relative symbol
1753 address encountered in the image.
1754
1755 On 64-bit builds, this reduces the size of the address table by 50%,
1756 but more importantly, it results in entries whose values are build
1757 time constants, and no relocation pass is required at runtime to fix
1758 up the entries based on the runtime load address of the kernel.
1759
1760 # end of the "standard kernel features (expert users)" menu
1761
1762 # syscall, maps, verifier
1763
1764 config ARCH_HAS_MEMBARRIER_CALLBACKS
1765 bool
1766
1767 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1768 bool
1769
1770 config KCMP
1771 bool "Enable kcmp() system call" if EXPERT
1772 help
1773 Enable the kernel resource comparison system call. It provides
1774 user-space with the ability to compare two processes to see if they
1775 share a common resource, such as a file descriptor or even virtual
1776 memory space.
1777
1778 If unsure, say N.
1779
1780 config RSEQ
1781 bool "Enable rseq() system call" if EXPERT
1782 default y
1783 depends on HAVE_RSEQ
1784 select MEMBARRIER
1785 help
1786 Enable the restartable sequences system call. It provides a
1787 user-space cache for the current CPU number value, which
1788 speeds up getting the current CPU number from user-space,
1789 as well as an ABI to speed up user-space operations on
1790 per-CPU data.
1791
1792 If unsure, say Y.
1793
1794 config DEBUG_RSEQ
1795 default n
1796 bool "Enabled debugging of rseq() system call" if EXPERT
1797 depends on RSEQ && DEBUG_KERNEL
1798 help
1799 Enable extra debugging checks for the rseq system call.
1800
1801 If unsure, say N.
1802
1803 config EMBEDDED
1804 bool "Embedded system"
1805 select EXPERT
1806 help
1807 This option should be enabled if compiling the kernel for
1808 an embedded system so certain expert options are available
1809 for configuration.
1810
1811 config HAVE_PERF_EVENTS
1812 bool
1813 help
1814 See tools/perf/design.txt for details.
1815
1816 config GUEST_PERF_EVENTS
1817 bool
1818 depends on HAVE_PERF_EVENTS
1819
1820 config PERF_USE_VMALLOC
1821 bool
1822 help
1823 See tools/perf/design.txt for details
1824
1825 config PC104
1826 bool "PC/104 support" if EXPERT
1827 help
1828 Expose PC/104 form factor device drivers and options available for
1829 selection and configuration. Enable this option if your target
1830 machine has a PC/104 bus.
1831
1832 menu "Kernel Performance Events And Counters"
1833
1834 config PERF_EVENTS
1835 bool "Kernel performance events and counters"
1836 default y if PROFILING
1837 depends on HAVE_PERF_EVENTS
1838 select IRQ_WORK
1839 select SRCU
1840 help
1841 Enable kernel support for various performance events provided
1842 by software and hardware.
1843
1844 Software events are supported either built-in or via the
1845 use of generic tracepoints.
1846
1847 Most modern CPUs support performance events via performance
1848 counter registers. These registers count the number of certain
1849 types of hw events: such as instructions executed, cachemisses
1850 suffered, or branches mis-predicted - without slowing down the
1851 kernel or applications. These registers can also trigger interrupts
1852 when a threshold number of events have passed - and can thus be
1853 used to profile the code that runs on that CPU.
1854
1855 The Linux Performance Event subsystem provides an abstraction of
1856 these software and hardware event capabilities, available via a
1857 system call and used by the "perf" utility in tools/perf/. It
1858 provides per task and per CPU counters, and it provides event
1859 capabilities on top of those.
1860
1861 Say Y if unsure.
1862
1863 config DEBUG_PERF_USE_VMALLOC
1864 default n
1865 bool "Debug: use vmalloc to back perf mmap() buffers"
1866 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1867 select PERF_USE_VMALLOC
1868 help
1869 Use vmalloc memory to back perf mmap() buffers.
1870
1871 Mostly useful for debugging the vmalloc code on platforms
1872 that don't require it.
1873
1874 Say N if unsure.
1875
1876 endmenu
1877
1878 config SYSTEM_DATA_VERIFICATION
1879 def_bool n
1880 select SYSTEM_TRUSTED_KEYRING
1881 select KEYS
1882 select CRYPTO
1883 select CRYPTO_RSA
1884 select ASYMMETRIC_KEY_TYPE
1885 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1886 select ASN1
1887 select OID_REGISTRY
1888 select X509_CERTIFICATE_PARSER
1889 select PKCS7_MESSAGE_PARSER
1890 help
1891 Provide PKCS#7 message verification using the contents of the system
1892 trusted keyring to provide public keys. This then can be used for
1893 module verification, kexec image verification and firmware blob
1894 verification.
1895
1896 config PROFILING
1897 bool "Profiling support"
1898 help
1899 Say Y here to enable the extended profiling support mechanisms used
1900 by profilers.
1901
1902 #
1903 # Place an empty function call at each tracepoint site. Can be
1904 # dynamically changed for a probe function.
1905 #
1906 config TRACEPOINTS
1907 bool
1908
1909 endmenu # General setup
1910
1911 source "arch/Kconfig"
1912
1913 config RT_MUTEXES
1914 bool
1915 default y if PREEMPT_RT
1916
1917 config BASE_SMALL
1918 int
1919 default 0 if BASE_FULL
1920 default 1 if !BASE_FULL
1921
1922 config MODULE_SIG_FORMAT
1923 def_bool n
1924 select SYSTEM_DATA_VERIFICATION
1925
1926 source "kernel/module/Kconfig"
1927
1928 config INIT_ALL_POSSIBLE
1929 bool
1930 help
1931 Back when each arch used to define their own cpu_online_mask and
1932 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1933 with all 1s, and others with all 0s. When they were centralised,
1934 it was better to provide this option than to break all the archs
1935 and have several arch maintainers pursuing me down dark alleys.
1936
1937 source "block/Kconfig"
1938
1939 config PREEMPT_NOTIFIERS
1940 bool
1941
1942 config PADATA
1943 depends on SMP
1944 bool
1945
1946 config ASN1
1947 tristate
1948 help
1949 Build a simple ASN.1 grammar compiler that produces a bytecode output
1950 that can be interpreted by the ASN.1 stream decoder and used to
1951 inform it as to what tags are to be expected in a stream and what
1952 functions to call on what tags.
1953
1954 source "kernel/Kconfig.locks"
1955
1956 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
1957 bool
1958
1959 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
1960 bool
1961
1962 # It may be useful for an architecture to override the definitions of the
1963 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
1964 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
1965 # different calling convention for syscalls. They can also override the
1966 # macros for not-implemented syscalls in kernel/sys_ni.c and
1967 # kernel/time/posix-stubs.c. All these overrides need to be available in
1968 # <asm/syscall_wrapper.h>.
1969 config ARCH_HAS_SYSCALL_WRAPPER
1970 def_bool n
