1 # SPDX-License-Identifier: GPL-2.0-only
4 default "$(CC_VERSION_TEXT)"
6 This is used in unclear ways:
8 - Re-run Kconfig when the compiler is updated
9 The 'default' property references the environment variable,
10 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
11 When the compiler is updated, Kconfig will be invoked.
13 - Ensure full rebuild when the compiler is updated
14 include/linux/compiler-version.h contains this option in the comment
15 line so fixdep adds include/config/CC_VERSION_TEXT into the
16 auto-generated dependency. When the compiler is updated, syncconfig
17 will touch it and then every file will be rebuilt.
20 def_bool $(success,test "$(cc-name)" = GCC)
24 default $(cc-version) if CC_IS_GCC
28 def_bool $(success,test "$(cc-name)" = Clang)
32 default $(cc-version) if CC_IS_CLANG
36 def_bool $(success,test "$(as-name)" = GNU)
39 def_bool $(success,test "$(as-name)" = LLVM)
43 # Use clang version if this is the integrated assembler
44 default CLANG_VERSION if AS_IS_LLVM
48 def_bool $(success,test "$(ld-name)" = BFD)
52 default $(ld-version) if LD_IS_BFD
56 def_bool $(success,test "$(ld-name)" = LLD)
60 default $(ld-version) if LD_IS_LLD
65 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
66 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
68 config CC_CAN_LINK_STATIC
70 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
71 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
73 config CC_HAS_ASM_GOTO
74 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
76 config CC_HAS_ASM_GOTO_OUTPUT
77 depends on CC_HAS_ASM_GOTO
78 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)
80 config CC_HAS_ASM_GOTO_TIED_OUTPUT
81 depends on CC_HAS_ASM_GOTO_OUTPUT
82 # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
83 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)
85 config TOOLS_SUPPORT_RELR
86 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
88 config CC_HAS_ASM_INLINE
89 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
91 config CC_HAS_NO_PROFILE_FN_ATTR
92 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
96 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
104 config BUILDTIME_TABLE_SORT
107 config THREAD_INFO_IN_TASK
110 Select this to move thread_info off the stack into task_struct. To
111 make this work, an arch will need to remove all thread_info fields
112 except flags and fix any runtime bugs.
114 One subtle change that will be needed is to use try_get_task_stack()
115 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
124 depends on BROKEN || !SMP
127 config INIT_ENV_ARG_LIMIT
132 Maximum of each of the number of arguments and environment
133 variables passed to init from the kernel command line.
136 bool "Compile also drivers which will not load"
139 Some drivers can be compiled on a different platform than they are
140 intended to be run on. Despite they cannot be loaded there (or even
141 when they load they cannot be used due to missing HW support),
142 developers still, opposing to distributors, might want to build such
143 drivers to compile-test them.
145 If you are a developer and want to build everything available, say Y
146 here. If you are a user/distributor, say N here to exclude useless
147 drivers to be distributed.
150 bool "Compile the kernel with warnings as errors"
153 A kernel build should not cause any compiler warnings, and this
154 enables the '-Werror' flag to enforce that rule by default.
156 However, if you have a new (or very old) compiler with odd and
157 unusual warnings, or you have some architecture with problems,
158 you may need to disable this config option in order to
159 successfully build the kernel.
163 config UAPI_HEADER_TEST
164 bool "Compile test UAPI headers"
165 depends on HEADERS_INSTALL && CC_CAN_LINK
167 Compile test headers exported to user-space to ensure they are
168 self-contained, i.e. compilable as standalone units.
170 If you are a developer or tester and want to ensure the exported
171 headers are self-contained, say Y here. Otherwise, choose N.
174 string "Local version - append to kernel release"
176 Append an extra string to the end of your kernel version.
177 This will show up when you type uname, for example.
178 The string you set here will be appended after the contents of
179 any files with a filename matching localversion* in your
180 object and source tree, in that order. Your total string can
181 be a maximum of 64 characters.
183 config LOCALVERSION_AUTO
184 bool "Automatically append version information to the version string"
186 depends on !COMPILE_TEST
188 This will try to automatically determine if the current tree is a
189 release tree by looking for git tags that belong to the current
190 top of tree revision.
192 A string of the format -gxxxxxxxx will be added to the localversion
193 if a git-based tree is found. The string generated by this will be
194 appended after any matching localversion* files, and after the value
195 set in CONFIG_LOCALVERSION.
197 (The actual string used here is the first eight characters produced
198 by running the command:
200 $ git rev-parse --verify HEAD
202 which is done within the script "scripts/setlocalversion".)
205 string "Build ID Salt"
208 The build ID is used to link binaries and their debug info. Setting
209 this option will use the value in the calculation of the build id.
210 This is mostly useful for distributions which want to ensure the
211 build is unique between builds. It's safe to leave the default.
213 config HAVE_KERNEL_GZIP
216 config HAVE_KERNEL_BZIP2
219 config HAVE_KERNEL_LZMA
222 config HAVE_KERNEL_XZ
225 config HAVE_KERNEL_LZO
228 config HAVE_KERNEL_LZ4
231 config HAVE_KERNEL_ZSTD
234 config HAVE_KERNEL_UNCOMPRESSED
238 prompt "Kernel compression mode"
240 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
242 The linux kernel is a kind of self-extracting executable.
243 Several compression algorithms are available, which differ
244 in efficiency, compression and decompression speed.
245 Compression speed is only relevant when building a kernel.
246 Decompression speed is relevant at each boot.
248 If you have any problems with bzip2 or lzma compressed
249 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
250 version of this functionality (bzip2 only), for 2.4, was
251 supplied by Christian Ludwig)
253 High compression options are mostly useful for users, who
254 are low on disk space (embedded systems), but for whom ram
257 If in doubt, select 'gzip'
261 depends on HAVE_KERNEL_GZIP
263 The old and tried gzip compression. It provides a good balance
264 between compression ratio and decompression speed.
268 depends on HAVE_KERNEL_BZIP2
270 Its compression ratio and speed is intermediate.
271 Decompression speed is slowest among the choices. The kernel
272 size is about 10% smaller with bzip2, in comparison to gzip.
273 Bzip2 uses a large amount of memory. For modern kernels you
274 will need at least 8MB RAM or more for booting.
278 depends on HAVE_KERNEL_LZMA
280 This compression algorithm's ratio is best. Decompression speed
281 is between gzip and bzip2. Compression is slowest.
282 The kernel size is about 33% smaller with LZMA in comparison to gzip.
286 depends on HAVE_KERNEL_XZ
288 XZ uses the LZMA2 algorithm and instruction set specific
289 BCJ filters which can improve compression ratio of executable
290 code. The size of the kernel is about 30% smaller with XZ in
291 comparison to gzip. On architectures for which there is a BCJ
292 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
293 will create a few percent smaller kernel than plain LZMA.
295 The speed is about the same as with LZMA: The decompression
296 speed of XZ is better than that of bzip2 but worse than gzip
297 and LZO. Compression is slow.
301 depends on HAVE_KERNEL_LZO
303 Its compression ratio is the poorest among the choices. The kernel
304 size is about 10% bigger than gzip; however its speed
305 (both compression and decompression) is the fastest.
309 depends on HAVE_KERNEL_LZ4
311 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
312 A preliminary version of LZ4 de/compression tool is available at
313 <https://code.google.com/p/lz4/>.
315 Its compression ratio is worse than LZO. The size of the kernel
316 is about 8% bigger than LZO. But the decompression speed is
321 depends on HAVE_KERNEL_ZSTD
323 ZSTD is a compression algorithm targeting intermediate compression
324 with fast decompression speed. It will compress better than GZIP and
325 decompress around the same speed as LZO, but slower than LZ4. You
326 will need at least 192 KB RAM or more for booting. The zstd command
327 line tool is required for compression.
329 config KERNEL_UNCOMPRESSED
331 depends on HAVE_KERNEL_UNCOMPRESSED
333 Produce uncompressed kernel image. This option is usually not what
334 you want. It is useful for debugging the kernel in slow simulation
335 environments, where decompressing and moving the kernel is awfully
336 slow. This option allows early boot code to skip the decompressor
337 and jump right at uncompressed kernel image.
342 string "Default init path"
345 This option determines the default init for the system if no init=
346 option is passed on the kernel command line. If the requested path is
347 not present, we will still then move on to attempting further
348 locations (e.g. /sbin/init, etc). If this is empty, we will just use
349 the fallback list when init= is not passed.
351 config DEFAULT_HOSTNAME
352 string "Default hostname"
355 This option determines the default system hostname before userspace
356 calls sethostname(2). The kernel traditionally uses "(none)" here,
357 but you may wish to use a different default here to make a minimal
358 system more usable with less configuration.
361 # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
362 # add proper SWAP support to them, in which case this can be remove.
368 bool "Support for paging of anonymous memory (swap)"
369 depends on MMU && BLOCK && !ARCH_NO_SWAP
372 This option allows you to choose whether you want to have support
373 for so called swap devices or swap files in your kernel that are
374 used to provide more virtual memory than the actual RAM present
375 in your computer. If unsure say Y.
380 Inter Process Communication is a suite of library functions and
381 system calls which let processes (running programs) synchronize and
382 exchange information. It is generally considered to be a good thing,
383 and some programs won't run unless you say Y here. In particular, if
384 you want to run the DOS emulator dosemu under Linux (read the
385 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
386 you'll need to say Y here.
388 You can find documentation about IPC with "info ipc" and also in
389 section 6.4 of the Linux Programmer's Guide, available from
390 <http://www.tldp.org/guides.html>.
392 config SYSVIPC_SYSCTL
399 bool "POSIX Message Queues"
402 POSIX variant of message queues is a part of IPC. In POSIX message
403 queues every message has a priority which decides about succession
404 of receiving it by a process. If you want to compile and run
405 programs written e.g. for Solaris with use of its POSIX message
406 queues (functions mq_*) say Y here.
408 POSIX message queues are visible as a filesystem called 'mqueue'
409 and can be mounted somewhere if you want to do filesystem
410 operations on message queues.
414 config POSIX_MQUEUE_SYSCTL
416 depends on POSIX_MQUEUE
421 bool "General notification queue"
425 This is a general notification queue for the kernel to pass events to
426 userspace by splicing them into pipes. It can be used in conjunction
427 with watches for key/keyring change notifications and device
430 See Documentation/watch_queue.rst
432 config CROSS_MEMORY_ATTACH
433 bool "Enable process_vm_readv/writev syscalls"
437 Enabling this option adds the system calls process_vm_readv and
438 process_vm_writev which allow a process with the correct privileges
439 to directly read from or write to another process' address space.
440 See the man page for more details.
443 bool "uselib syscall"
444 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
446 This option enables the uselib syscall, a system call used in the
447 dynamic linker from libc5 and earlier. glibc does not use this
448 system call. If you intend to run programs built on libc5 or
449 earlier, you may need to enable this syscall. Current systems
450 running glibc can safely disable this.
453 bool "Auditing support"
456 Enable auditing infrastructure that can be used with another
457 kernel subsystem, such as SELinux (which requires this for
458 logging of avc messages output). System call auditing is included
459 on architectures which support it.
461 config HAVE_ARCH_AUDITSYSCALL
466 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
469 source "kernel/irq/Kconfig"
470 source "kernel/time/Kconfig"
471 source "kernel/bpf/Kconfig"
472 source "kernel/Kconfig.preempt"
474 menu "CPU/Task time and stats accounting"
476 config VIRT_CPU_ACCOUNTING
480 prompt "Cputime accounting"
481 default TICK_CPU_ACCOUNTING if !PPC64
482 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
484 # Kind of a stub config for the pure tick based cputime accounting
485 config TICK_CPU_ACCOUNTING
486 bool "Simple tick based cputime accounting"
487 depends on !S390 && !NO_HZ_FULL
489 This is the basic tick based cputime accounting that maintains
490 statistics about user, system and idle time spent on per jiffies
495 config VIRT_CPU_ACCOUNTING_NATIVE
496 bool "Deterministic task and CPU time accounting"
497 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
498 select VIRT_CPU_ACCOUNTING
500 Select this option to enable more accurate task and CPU time
501 accounting. This is done by reading a CPU counter on each
502 kernel entry and exit and on transitions within the kernel
503 between system, softirq and hardirq state, so there is a
504 small performance impact. In the case of s390 or IBM POWER > 5,
505 this also enables accounting of stolen time on logically-partitioned
508 config VIRT_CPU_ACCOUNTING_GEN
509 bool "Full dynticks CPU time accounting"
510 depends on HAVE_CONTEXT_TRACKING
511 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
512 depends on GENERIC_CLOCKEVENTS
513 select VIRT_CPU_ACCOUNTING
514 select CONTEXT_TRACKING
516 Select this option to enable task and CPU time accounting on full
517 dynticks systems. This accounting is implemented by watching every
518 kernel-user boundaries using the context tracking subsystem.
519 The accounting is thus performed at the expense of some significant
522 For now this is only useful if you are working on the full
523 dynticks subsystem development.
529 config IRQ_TIME_ACCOUNTING
530 bool "Fine granularity task level IRQ time accounting"
531 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
533 Select this option to enable fine granularity task irq time
534 accounting. This is done by reading a timestamp on each
535 transitions between softirq and hardirq state, so there can be a
536 small performance impact.
538 If in doubt, say N here.
540 config HAVE_SCHED_AVG_IRQ
542 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
545 config SCHED_THERMAL_PRESSURE
547 default y if ARM && ARM_CPU_TOPOLOGY
550 depends on CPU_FREQ_THERMAL
552 Select this option to enable thermal pressure accounting in the
553 scheduler. Thermal pressure is the value conveyed to the scheduler
554 that reflects the reduction in CPU compute capacity resulted from
555 thermal throttling. Thermal throttling occurs when the performance of
556 a CPU is capped due to high operating temperatures.
558 If selected, the scheduler will be able to balance tasks accordingly,
559 i.e. put less load on throttled CPUs than on non/less throttled ones.
561 This requires the architecture to implement
562 arch_update_thermal_pressure() and arch_scale_thermal_pressure().
564 config BSD_PROCESS_ACCT
565 bool "BSD Process Accounting"
568 If you say Y here, a user level program will be able to instruct the
569 kernel (via a special system call) to write process accounting
570 information to a file: whenever a process exits, information about
571 that process will be appended to the file by the kernel. The
572 information includes things such as creation time, owning user,
573 command name, memory usage, controlling terminal etc. (the complete
574 list is in the struct acct in <file:include/linux/acct.h>). It is
575 up to the user level program to do useful things with this
576 information. This is generally a good idea, so say Y.
578 config BSD_PROCESS_ACCT_V3
579 bool "BSD Process Accounting version 3 file format"
580 depends on BSD_PROCESS_ACCT
583 If you say Y here, the process accounting information is written
584 in a new file format that also logs the process IDs of each
585 process and its parent. Note that this file format is incompatible
586 with previous v0/v1/v2 file formats, so you will need updated tools
587 for processing it. A preliminary version of these tools is available
588 at <http://www.gnu.org/software/acct/>.
591 bool "Export task/process statistics through netlink"
596 Export selected statistics for tasks/processes through the
597 generic netlink interface. Unlike BSD process accounting, the
598 statistics are available during the lifetime of tasks/processes as
599 responses to commands. Like BSD accounting, they are sent to user
604 config TASK_DELAY_ACCT
605 bool "Enable per-task delay accounting"
609 Collect information on time spent by a task waiting for system
610 resources like cpu, synchronous block I/O completion and swapping
611 in pages. Such statistics can help in setting a task's priorities
612 relative to other tasks for cpu, io, rss limits etc.
617 bool "Enable extended accounting over taskstats"
620 Collect extended task accounting data and send the data
621 to userland for processing over the taskstats interface.
625 config TASK_IO_ACCOUNTING
626 bool "Enable per-task storage I/O accounting"
627 depends on TASK_XACCT
629 Collect information on the number of bytes of storage I/O which this
635 bool "Pressure stall information tracking"
637 Collect metrics that indicate how overcommitted the CPU, memory,
638 and IO capacity are in the system.
640 If you say Y here, the kernel will create /proc/pressure/ with the
641 pressure statistics files cpu, memory, and io. These will indicate
642 the share of walltime in which some or all tasks in the system are
643 delayed due to contention of the respective resource.
645 In kernels with cgroup support, cgroups (cgroup2 only) will
646 have cpu.pressure, memory.pressure, and io.pressure files,
647 which aggregate pressure stalls for the grouped tasks only.
649 For more details see Documentation/accounting/psi.rst.
653 config PSI_DEFAULT_DISABLED
654 bool "Require boot parameter to enable pressure stall information tracking"
658 If set, pressure stall information tracking will be disabled
659 per default but can be enabled through passing psi=1 on the
660 kernel commandline during boot.
662 This feature adds some code to the task wakeup and sleep
663 paths of the scheduler. The overhead is too low to affect
664 common scheduling-intense workloads in practice (such as
665 webservers, memcache), but it does show up in artificial
666 scheduler stress tests, such as hackbench.
668 If you are paranoid and not sure what the kernel will be
673 endmenu # "CPU/Task time and stats accounting"
677 depends on SMP || COMPILE_TEST
680 Make sure that CPUs running critical tasks are not disturbed by
681 any source of "noise" such as unbound workqueues, timers, kthreads...
682 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
683 the "isolcpus=" boot parameter.
687 source "kernel/rcu/Kconfig"
694 tristate "Kernel .config support"
696 This option enables the complete Linux kernel ".config" file
697 contents to be saved in the kernel. It provides documentation
698 of which kernel options are used in a running kernel or in an
699 on-disk kernel. This information can be extracted from the kernel
700 image file with the script scripts/extract-ikconfig and used as
701 input to rebuild the current kernel or to build another kernel.
702 It can also be extracted from a running kernel by reading
703 /proc/config.gz if enabled (below).
706 bool "Enable access to .config through /proc/config.gz"
707 depends on IKCONFIG && PROC_FS
709 This option enables access to the kernel configuration file
710 through /proc/config.gz.
713 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
716 This option enables access to the in-kernel headers that are generated during
717 the build process. These can be used to build eBPF tracing programs,
718 or similar programs. If you build the headers as a module, a module called
719 kheaders.ko is built which can be loaded on-demand to get access to headers.
722 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
723 range 12 25 if !H8300
728 Select the minimal kernel log buffer size as a power of 2.
729 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
730 parameter, see below. Any higher size also might be forced
731 by "log_buf_len" boot parameter.
741 config LOG_CPU_MAX_BUF_SHIFT
742 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
745 default 12 if !BASE_SMALL
746 default 0 if BASE_SMALL
749 This option allows to increase the default ring buffer size
750 according to the number of CPUs. The value defines the contribution
751 of each CPU as a power of 2. The used space is typically only few
752 lines however it might be much more when problems are reported,
755 The increased size means that a new buffer has to be allocated and
756 the original static one is unused. It makes sense only on systems
757 with more CPUs. Therefore this value is used only when the sum of
758 contributions is greater than the half of the default kernel ring
759 buffer as defined by LOG_BUF_SHIFT. The default values are set
760 so that more than 16 CPUs are needed to trigger the allocation.
762 Also this option is ignored when "log_buf_len" kernel parameter is
763 used as it forces an exact (power of two) size of the ring buffer.
765 The number of possible CPUs is used for this computation ignoring
766 hotplugging making the computation optimal for the worst case
767 scenario while allowing a simple algorithm to be used from bootup.
769 Examples shift values and their meaning:
770 17 => 128 KB for each CPU
771 16 => 64 KB for each CPU
772 15 => 32 KB for each CPU
773 14 => 16 KB for each CPU
774 13 => 8 KB for each CPU
775 12 => 4 KB for each CPU
777 config PRINTK_SAFE_LOG_BUF_SHIFT
778 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
783 Select the size of an alternate printk per-CPU buffer where messages
784 printed from usafe contexts are temporary stored. One example would
785 be NMI messages, another one - printk recursion. The messages are
786 copied to the main log buffer in a safe context to avoid a deadlock.
787 The value defines the size as a power of 2.
789 Those messages are rare and limited. The largest one is when
790 a backtrace is printed. It usually fits into 4KB. Select
791 8KB if you want to be on the safe side.
794 17 => 128 KB for each CPU
795 16 => 64 KB for each CPU
796 15 => 32 KB for each CPU
797 14 => 16 KB for each CPU
798 13 => 8 KB for each CPU
799 12 => 4 KB for each CPU
802 bool "Printk indexing debugfs interface"
803 depends on PRINTK && DEBUG_FS
805 Add support for indexing of all printk formats known at compile time
806 at <debugfs>/printk/index/<module>.
808 This can be used as part of maintaining daemons which monitor
809 /dev/kmsg, as it permits auditing the printk formats present in a
810 kernel, allowing detection of cases where monitored printks are
811 changed or no longer present.
813 There is no additional runtime cost to printk with this enabled.
816 # Architectures with an unreliable sched_clock() should select this:
818 config HAVE_UNSTABLE_SCHED_CLOCK
821 config GENERIC_SCHED_CLOCK
824 menu "Scheduler features"
827 bool "Enable utilization clamping for RT/FAIR tasks"
828 depends on CPU_FREQ_GOV_SCHEDUTIL
830 This feature enables the scheduler to track the clamped utilization
831 of each CPU based on RUNNABLE tasks scheduled on that CPU.
833 With this option, the user can specify the min and max CPU
834 utilization allowed for RUNNABLE tasks. The max utilization defines
835 the maximum frequency a task should use while the min utilization
836 defines the minimum frequency it should use.
838 Both min and max utilization clamp values are hints to the scheduler,
839 aiming at improving its frequency selection policy, but they do not
840 enforce or grant any specific bandwidth for tasks.
844 config UCLAMP_BUCKETS_COUNT
845 int "Number of supported utilization clamp buckets"
848 depends on UCLAMP_TASK
850 Defines the number of clamp buckets to use. The range of each bucket
851 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
852 number of clamp buckets the finer their granularity and the higher
853 the precision of clamping aggregation and tracking at run-time.
855 For example, with the minimum configuration value we will have 5
856 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
857 be refcounted in the [20..39]% bucket and will set the bucket clamp
858 effective value to 25%.
859 If a second 30% boosted task should be co-scheduled on the same CPU,
860 that task will be refcounted in the same bucket of the first task and
861 it will boost the bucket clamp effective value to 30%.
862 The clamp effective value of a bucket is reset to its nominal value
863 (20% in the example above) when there are no more tasks refcounted in
866 An additional boost/capping margin can be added to some tasks. In the
867 example above the 25% task will be boosted to 30% until it exits the
868 CPU. If that should be considered not acceptable on certain systems,
869 it's always possible to reduce the margin by increasing the number of
870 clamp buckets to trade off used memory for run-time tracking
873 If in doubt, use the default value.
878 # For architectures that want to enable the support for NUMA-affine scheduler
881 config ARCH_SUPPORTS_NUMA_BALANCING
885 # For architectures that prefer to flush all TLBs after a number of pages
886 # are unmapped instead of sending one IPI per page to flush. The architecture
887 # must provide guarantees on what happens if a clean TLB cache entry is
888 # written after the unmap. Details are in mm/rmap.c near the check for
889 # should_defer_flush. The architecture should also consider if the full flush
890 # and the refill costs are offset by the savings of sending fewer IPIs.
891 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
895 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
897 config CC_IMPLICIT_FALLTHROUGH
899 default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
900 default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
903 # For architectures that know their GCC __int128 support is sound
905 config ARCH_SUPPORTS_INT128
908 # For architectures that (ab)use NUMA to represent different memory regions
909 # all cpu-local but of different latencies, such as SuperH.
911 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
914 config NUMA_BALANCING
915 bool "Memory placement aware NUMA scheduler"
916 depends on ARCH_SUPPORTS_NUMA_BALANCING
917 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
918 depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
920 This option adds support for automatic NUMA aware memory/task placement.
921 The mechanism is quite primitive and is based on migrating memory when
922 it has references to the node the task is running on.
924 This system will be inactive on UMA systems.
926 config NUMA_BALANCING_DEFAULT_ENABLED
927 bool "Automatically enable NUMA aware memory/task placement"
929 depends on NUMA_BALANCING
931 If set, automatic NUMA balancing will be enabled if running on a NUMA
935 bool "Control Group support"
938 This option adds support for grouping sets of processes together, for
939 use with process control subsystems such as Cpusets, CFS, memory
940 controls or device isolation.
942 - Documentation/scheduler/sched-design-CFS.rst (CFS)
943 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
944 and resource control)
954 bool "Memory controller"
958 Provides control over the memory footprint of tasks in a cgroup.
962 depends on MEMCG && SWAP
967 depends on MEMCG && !SLOB
975 Generic block IO controller cgroup interface. This is the common
976 cgroup interface which should be used by various IO controlling
979 Currently, CFQ IO scheduler uses it to recognize task groups and
980 control disk bandwidth allocation (proportional time slice allocation)
981 to such task groups. It is also used by bio throttling logic in
982 block layer to implement upper limit in IO rates on a device.
984 This option only enables generic Block IO controller infrastructure.
985 One needs to also enable actual IO controlling logic/policy. For
986 enabling proportional weight division of disk bandwidth in CFQ, set
987 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
988 CONFIG_BLK_DEV_THROTTLING=y.
990 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
992 config CGROUP_WRITEBACK
994 depends on MEMCG && BLK_CGROUP
997 menuconfig CGROUP_SCHED
998 bool "CPU controller"
1001 This feature lets CPU scheduler recognize task groups and control CPU
1002 bandwidth allocation to such task groups. It uses cgroups to group
1006 config FAIR_GROUP_SCHED
1007 bool "Group scheduling for SCHED_OTHER"
1008 depends on CGROUP_SCHED
1009 default CGROUP_SCHED
1011 config CFS_BANDWIDTH
1012 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1013 depends on FAIR_GROUP_SCHED
1016 This option allows users to define CPU bandwidth rates (limits) for
1017 tasks running within the fair group scheduler. Groups with no limit
1018 set are considered to be unconstrained and will run with no
1020 See Documentation/scheduler/sched-bwc.rst for more information.
1022 config RT_GROUP_SCHED
1023 bool "Group scheduling for SCHED_RR/FIFO"
1024 depends on CGROUP_SCHED
1027 This feature lets you explicitly allocate real CPU bandwidth
1028 to task groups. If enabled, it will also make it impossible to
1029 schedule realtime tasks for non-root users until you allocate
1030 realtime bandwidth for them.
1031 See Documentation/scheduler/sched-rt-group.rst for more information.
1035 config UCLAMP_TASK_GROUP
1036 bool "Utilization clamping per group of tasks"
1037 depends on CGROUP_SCHED
1038 depends on UCLAMP_TASK
1041 This feature enables the scheduler to track the clamped utilization
1042 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
1044 When this option is enabled, the user can specify a min and max
1045 CPU bandwidth which is allowed for each single task in a group.
1046 The max bandwidth allows to clamp the maximum frequency a task
1047 can use, while the min bandwidth allows to define a minimum
1048 frequency a task will always use.
1050 When task group based utilization clamping is enabled, an eventually
1051 specified task-specific clamp value is constrained by the cgroup
1052 specified clamp value. Both minimum and maximum task clamping cannot
1053 be bigger than the corresponding clamping defined at task group level.
1058 bool "PIDs controller"
1060 Provides enforcement of process number limits in the scope of a
1061 cgroup. Any attempt to fork more processes than is allowed in the
1062 cgroup will fail. PIDs are fundamentally a global resource because it
1063 is fairly trivial to reach PID exhaustion before you reach even a
1064 conservative kmemcg limit. As a result, it is possible to grind a
1065 system to halt without being limited by other cgroup policies. The
1066 PIDs controller is designed to stop this from happening.
1068 It should be noted that organisational operations (such as attaching
1069 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1070 since the PIDs limit only affects a process's ability to fork, not to
1074 bool "RDMA controller"
1076 Provides enforcement of RDMA resources defined by IB stack.
1077 It is fairly easy for consumers to exhaust RDMA resources, which
1078 can result into resource unavailability to other consumers.
1079 RDMA controller is designed to stop this from happening.
1080 Attaching processes with active RDMA resources to the cgroup
1081 hierarchy is allowed even if can cross the hierarchy's limit.
1083 config CGROUP_FREEZER
1084 bool "Freezer controller"
1086 Provides a way to freeze and unfreeze all tasks in a
1089 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1090 controller includes important in-kernel memory consumers per default.
1092 If you're using cgroup2, say N.
1094 config CGROUP_HUGETLB
1095 bool "HugeTLB controller"
1096 depends on HUGETLB_PAGE
1100 Provides a cgroup controller for HugeTLB pages.
1101 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1102 The limit is enforced during page fault. Since HugeTLB doesn't
1103 support page reclaim, enforcing the limit at page fault time implies
1104 that, the application will get SIGBUS signal if it tries to access
1105 HugeTLB pages beyond its limit. This requires the application to know
1106 beforehand how much HugeTLB pages it would require for its use. The
1107 control group is tracked in the third page lru pointer. This means
1108 that we cannot use the controller with huge page less than 3 pages.
1111 bool "Cpuset controller"
1114 This option will let you create and manage CPUSETs which
1115 allow dynamically partitioning a system into sets of CPUs and
1116 Memory Nodes and assigning tasks to run only within those sets.
1117 This is primarily useful on large SMP or NUMA systems.
1121 config PROC_PID_CPUSET
1122 bool "Include legacy /proc/<pid>/cpuset file"
1126 config CGROUP_DEVICE
1127 bool "Device controller"
1129 Provides a cgroup controller implementing whitelists for
1130 devices which a process in the cgroup can mknod or open.
1132 config CGROUP_CPUACCT
1133 bool "Simple CPU accounting controller"
1135 Provides a simple controller for monitoring the
1136 total CPU consumed by the tasks in a cgroup.
1139 bool "Perf controller"
1140 depends on PERF_EVENTS
1142 This option extends the perf per-cpu mode to restrict monitoring
1143 to threads which belong to the cgroup specified and run on the
1144 designated cpu. Or this can be used to have cgroup ID in samples
1145 so that it can monitor performance events among cgroups.
1150 bool "Support for eBPF programs attached to cgroups"
1151 depends on BPF_SYSCALL
1152 select SOCK_CGROUP_DATA
1154 Allow attaching eBPF programs to a cgroup using the bpf(2)
1155 syscall command BPF_PROG_ATTACH.
1157 In which context these programs are accessed depends on the type
1158 of attachment. For instance, programs that are attached using
1159 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1163 bool "Misc resource controller"
1166 Provides a controller for miscellaneous resources on a host.
1168 Miscellaneous scalar resources are the resources on the host system
1169 which cannot be abstracted like the other cgroups. This controller
1170 tracks and limits the miscellaneous resources used by a process
1171 attached to a cgroup hierarchy.
1173 For more information, please check misc cgroup section in
1174 /Documentation/admin-guide/cgroup-v2.rst.
1177 bool "Debug controller"
1179 depends on DEBUG_KERNEL
1181 This option enables a simple controller that exports
1182 debugging information about the cgroups framework. This
1183 controller is for control cgroup debugging only. Its
1184 interfaces are not stable.
1188 config SOCK_CGROUP_DATA
1194 menuconfig NAMESPACES
1195 bool "Namespaces support" if EXPERT
1196 depends on MULTIUSER
1199 Provides the way to make tasks work with different objects using
1200 the same id. For example same IPC id may refer to different objects
1201 or same user id or pid may refer to different tasks when used in
1202 different namespaces.
1207 bool "UTS namespace"
1210 In this namespace tasks see different info provided with the
1214 bool "TIME namespace"
1215 depends on GENERIC_VDSO_TIME_NS
1218 In this namespace boottime and monotonic clocks can be set.
1219 The time will keep going with the same pace.
1222 bool "IPC namespace"
1223 depends on (SYSVIPC || POSIX_MQUEUE)
1226 In this namespace tasks work with IPC ids which correspond to
1227 different IPC objects in different namespaces.
1230 bool "User namespace"
1233 This allows containers, i.e. vservers, to use user namespaces
1234 to provide different user info for different servers.
1236 When user namespaces are enabled in the kernel it is
1237 recommended that the MEMCG option also be enabled and that
1238 user-space use the memory control groups to limit the amount
1239 of memory a memory unprivileged users can use.
1244 bool "PID Namespaces"
1247 Support process id namespaces. This allows having multiple
1248 processes with the same pid as long as they are in different
1249 pid namespaces. This is a building block of containers.
1252 bool "Network namespace"
1256 Allow user space to create what appear to be multiple instances
1257 of the network stack.
1261 config CHECKPOINT_RESTORE
1262 bool "Checkpoint/restore support"
1263 select PROC_CHILDREN
1267 Enables additional kernel features in a sake of checkpoint/restore.
1268 In particular it adds auxiliary prctl codes to setup process text,
1269 data and heap segment sizes, and a few additional /proc filesystem
1272 If unsure, say N here.
1274 config SCHED_AUTOGROUP
1275 bool "Automatic process group scheduling"
1278 select FAIR_GROUP_SCHED
1280 This option optimizes the scheduler for common desktop workloads by
1281 automatically creating and populating task groups. This separation
1282 of workloads isolates aggressive CPU burners (like build jobs) from
1283 desktop applications. Task group autogeneration is currently based
1286 config SYSFS_DEPRECATED
1287 bool "Enable deprecated sysfs features to support old userspace tools"
1291 This option adds code that switches the layout of the "block" class
1292 devices, to not show up in /sys/class/block/, but only in
1295 This switch is only active when the sysfs.deprecated=1 boot option is
1296 passed or the SYSFS_DEPRECATED_V2 option is set.
1298 This option allows new kernels to run on old distributions and tools,
1299 which might get confused by /sys/class/block/. Since 2007/2008 all
1300 major distributions and tools handle this just fine.
1302 Recent distributions and userspace tools after 2009/2010 depend on
1303 the existence of /sys/class/block/, and will not work with this
1306 Only if you are using a new kernel on an old distribution, you might
1309 config SYSFS_DEPRECATED_V2
1310 bool "Enable deprecated sysfs features by default"
1313 depends on SYSFS_DEPRECATED
1315 Enable deprecated sysfs by default.
1317 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1320 Only if you are using a new kernel on an old distribution, you might
1321 need to say Y here. Even then, odds are you would not need it
1322 enabled, you can always pass the boot option if absolutely necessary.
1325 bool "Kernel->user space relay support (formerly relayfs)"
1328 This option enables support for relay interface support in
1329 certain file systems (such as debugfs).
1330 It is designed to provide an efficient mechanism for tools and
1331 facilities to relay large amounts of data from kernel space to
1336 config BLK_DEV_INITRD
1337 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1339 The initial RAM filesystem is a ramfs which is loaded by the
1340 boot loader (loadlin or lilo) and that is mounted as root
1341 before the normal boot procedure. It is typically used to
1342 load modules needed to mount the "real" root file system,
1343 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1345 If RAM disk support (BLK_DEV_RAM) is also included, this
1346 also enables initial RAM disk (initrd) support and adds
1347 15 Kbytes (more on some other architectures) to the kernel size.
1353 source "usr/Kconfig"
1358 bool "Boot config support"
1359 select BLK_DEV_INITRD
1361 Extra boot config allows system admin to pass a config file as
1362 complemental extension of kernel cmdline when booting.
1363 The boot config file must be attached at the end of initramfs
1364 with checksum, size and magic word.
1365 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1370 prompt "Compiler optimization level"
1371 default CC_OPTIMIZE_FOR_PERFORMANCE
1373 config CC_OPTIMIZE_FOR_PERFORMANCE
1374 bool "Optimize for performance (-O2)"
1376 This is the default optimization level for the kernel, building
1377 with the "-O2" compiler flag for best performance and most
1378 helpful compile-time warnings.
1380 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1381 bool "Optimize more for performance (-O3)"
1384 Choosing this option will pass "-O3" to your compiler to optimize
1385 the kernel yet more for performance.
1387 config CC_OPTIMIZE_FOR_SIZE
1388 bool "Optimize for size (-Os)"
1390 Choosing this option will pass "-Os" to your compiler resulting
1391 in a smaller kernel.
1395 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1398 This requires that the arch annotates or otherwise protects
1399 its external entry points from being discarded. Linker scripts
1400 must also merge .text.*, .data.*, and .bss.* correctly into
1401 output sections. Care must be taken not to pull in unrelated
1402 sections (e.g., '.text.init'). Typically '.' in section names
1403 is used to distinguish them from label names / C identifiers.
1405 config LD_DEAD_CODE_DATA_ELIMINATION
1406 bool "Dead code and data elimination (EXPERIMENTAL)"
1407 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1409 depends on $(cc-option,-ffunction-sections -fdata-sections)
1410 depends on $(ld-option,--gc-sections)
1412 Enable this if you want to do dead code and data elimination with
1413 the linker by compiling with -ffunction-sections -fdata-sections,
1414 and linking with --gc-sections.
1416 This can reduce on disk and in-memory size of the kernel
1417 code and static data, particularly for small configs and
1418 on small systems. This has the possibility of introducing
1419 silently broken kernel if the required annotations are not
1420 present. This option is not well tested yet, so use at your
1423 config LD_ORPHAN_WARN
1425 depends on ARCH_WANT_LD_ORPHAN_WARN
1426 depends on $(ld-option,--orphan-handling=warn)
1434 config SYSCTL_EXCEPTION_TRACE
1437 Enable support for /proc/sys/debug/exception-trace.
1439 config SYSCTL_ARCH_UNALIGN_NO_WARN
1442 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1443 Allows arch to define/use @no_unaligned_warning to possibly warn
1444 about unaligned access emulation going on under the hood.
1446 config SYSCTL_ARCH_UNALIGN_ALLOW
1449 Enable support for /proc/sys/kernel/unaligned-trap
1450 Allows arches to define/use @unaligned_enabled to runtime toggle
1451 the unaligned access emulation.
1452 see arch/parisc/kernel/unaligned.c for reference
1454 config HAVE_PCSPKR_PLATFORM
1457 # interpreter that classic socket filters depend on
1462 bool "Configure standard kernel features (expert users)"
1463 # Unhide debug options, to make the on-by-default options visible
1466 This option allows certain base kernel options and settings
1467 to be disabled or tweaked. This is for specialized
1468 environments which can tolerate a "non-standard" kernel.
1469 Only use this if you really know what you are doing.
1472 bool "Enable 16-bit UID system calls" if EXPERT
1473 depends on HAVE_UID16 && MULTIUSER
1476 This enables the legacy 16-bit UID syscall wrappers.
1479 bool "Multiple users, groups and capabilities support" if EXPERT
1482 This option enables support for non-root users, groups and
1485 If you say N here, all processes will run with UID 0, GID 0, and all
1486 possible capabilities. Saying N here also compiles out support for
1487 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1490 If unsure, say Y here.
1492 config SGETMASK_SYSCALL
1493 bool "sgetmask/ssetmask syscalls support" if EXPERT
1494 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1496 sys_sgetmask and sys_ssetmask are obsolete system calls
1497 no longer supported in libc but still enabled by default in some
1500 If unsure, leave the default option here.
1502 config SYSFS_SYSCALL
1503 bool "Sysfs syscall support" if EXPERT
1506 sys_sysfs is an obsolete system call no longer supported in libc.
1507 Note that disabling this option is more secure but might break
1508 compatibility with some systems.
1510 If unsure say Y here.
1513 bool "open by fhandle syscalls" if EXPERT
1517 If you say Y here, a user level program will be able to map
1518 file names to handle and then later use the handle for
1519 different file system operations. This is useful in implementing
1520 userspace file servers, which now track files using handles instead
1521 of names. The handle would remain the same even if file names
1522 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1526 bool "Posix Clocks & timers" if EXPERT
1529 This includes native support for POSIX timers to the kernel.
1530 Some embedded systems have no use for them and therefore they
1531 can be configured out to reduce the size of the kernel image.
1533 When this option is disabled, the following syscalls won't be
1534 available: timer_create, timer_gettime: timer_getoverrun,
1535 timer_settime, timer_delete, clock_adjtime, getitimer,
1536 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1537 clock_getres and clock_nanosleep syscalls will be limited to
1538 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1544 bool "Enable support for printk" if EXPERT
1547 This option enables normal printk support. Removing it
1548 eliminates most of the message strings from the kernel image
1549 and makes the kernel more or less silent. As this makes it
1550 very difficult to diagnose system problems, saying N here is
1551 strongly discouraged.
1554 bool "BUG() support" if EXPERT
1557 Disabling this option eliminates support for BUG and WARN, reducing
1558 the size of your kernel image and potentially quietly ignoring
1559 numerous fatal conditions. You should only consider disabling this
1560 option for embedded systems with no facilities for reporting errors.
1566 bool "Enable ELF core dumps" if EXPERT
1568 Enable support for generating core dumps. Disabling saves about 4k.
1571 config PCSPKR_PLATFORM
1572 bool "Enable PC-Speaker support" if EXPERT
1573 depends on HAVE_PCSPKR_PLATFORM
1577 This option allows to disable the internal PC-Speaker
1578 support, saving some memory.
1582 bool "Enable full-sized data structures for core" if EXPERT
1584 Disabling this option reduces the size of miscellaneous core
1585 kernel data structures. This saves memory on small machines,
1586 but may reduce performance.
1589 bool "Enable futex support" if EXPERT
1590 depends on !(SPARC32 && SMP)
1594 Disabling this option will cause the kernel to be built without
1595 support for "fast userspace mutexes". The resulting kernel may not
1596 run glibc-based applications correctly.
1600 depends on FUTEX && RT_MUTEXES
1604 bool "Enable eventpoll support" if EXPERT
1607 Disabling this option will cause the kernel to be built without
1608 support for epoll family of system calls.
1611 bool "Enable signalfd() system call" if EXPERT
1614 Enable the signalfd() system call that allows to receive signals
1615 on a file descriptor.
1620 bool "Enable timerfd() system call" if EXPERT
1623 Enable the timerfd() system call that allows to receive timer
1624 events on a file descriptor.
1629 bool "Enable eventfd() system call" if EXPERT
1632 Enable the eventfd() system call that allows to receive both
1633 kernel notification (ie. KAIO) or userspace notifications.
1638 bool "Use full shmem filesystem" if EXPERT
1642 The shmem is an internal filesystem used to manage shared memory.
1643 It is backed by swap and manages resource limits. It is also exported
1644 to userspace as tmpfs if TMPFS is enabled. Disabling this
1645 option replaces shmem and tmpfs with the much simpler ramfs code,
1646 which may be appropriate on small systems without swap.
1649 bool "Enable AIO support" if EXPERT
1652 This option enables POSIX asynchronous I/O which may by used
1653 by some high performance threaded applications. Disabling
1654 this option saves about 7k.
1657 bool "Enable IO uring support" if EXPERT
1661 This option enables support for the io_uring interface, enabling
1662 applications to submit and complete IO through submission and
1663 completion rings that are shared between the kernel and application.
1665 config ADVISE_SYSCALLS
1666 bool "Enable madvise/fadvise syscalls" if EXPERT
1669 This option enables the madvise and fadvise syscalls, used by
1670 applications to advise the kernel about their future memory or file
1671 usage, improving performance. If building an embedded system where no
1672 applications use these syscalls, you can disable this option to save
1675 config HAVE_ARCH_USERFAULTFD_WP
1678 Arch has userfaultfd write protection support
1680 config HAVE_ARCH_USERFAULTFD_MINOR
1683 Arch has userfaultfd minor fault support
1686 bool "Enable membarrier() system call" if EXPERT
1689 Enable the membarrier() system call that allows issuing memory
1690 barriers across all running threads, which can be used to distribute
1691 the cost of user-space memory barriers asymmetrically by transforming
1692 pairs of memory barriers into pairs consisting of membarrier() and a
1698 bool "Load all symbols for debugging/ksymoops" if EXPERT
1701 Say Y here to let the kernel print out symbolic crash information and
1702 symbolic stack backtraces. This increases the size of the kernel
1703 somewhat, as all symbols have to be loaded into the kernel image.
1706 bool "Include all symbols in kallsyms"
1707 depends on DEBUG_KERNEL && KALLSYMS
1709 Normally kallsyms only contains the symbols of functions for nicer
1710 OOPS messages and backtraces (i.e., symbols from the text and inittext
1711 sections). This is sufficient for most cases. And only in very rare
1712 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1713 names of variables from the data sections, etc).
1715 This option makes sure that all symbols are loaded into the kernel
1716 image (i.e., symbols from all sections) in cost of increased kernel
1717 size (depending on the kernel configuration, it may be 300KiB or
1718 something like this).
1720 Say N unless you really need all symbols.
1722 config KALLSYMS_ABSOLUTE_PERCPU
1725 default X86_64 && SMP
1727 config KALLSYMS_BASE_RELATIVE
1732 Instead of emitting them as absolute values in the native word size,
1733 emit the symbol references in the kallsyms table as 32-bit entries,
1734 each containing a relative value in the range [base, base + U32_MAX]
1735 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1736 an absolute value in the range [0, S32_MAX] or a relative value in the
1737 range [base, base + S32_MAX], where base is the lowest relative symbol
1738 address encountered in the image.
1740 On 64-bit builds, this reduces the size of the address table by 50%,
1741 but more importantly, it results in entries whose values are build
1742 time constants, and no relocation pass is required at runtime to fix
1743 up the entries based on the runtime load address of the kernel.
1745 # end of the "standard kernel features (expert users)" menu
1747 # syscall, maps, verifier
1750 bool "Enable userfaultfd() system call"
1753 Enable the userfaultfd() system call that allows to intercept and
1754 handle page faults in userland.
1756 config ARCH_HAS_MEMBARRIER_CALLBACKS
1759 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1763 bool "Enable kcmp() system call" if EXPERT
1765 Enable the kernel resource comparison system call. It provides
1766 user-space with the ability to compare two processes to see if they
1767 share a common resource, such as a file descriptor or even virtual
1773 bool "Enable rseq() system call" if EXPERT
1775 depends on HAVE_RSEQ
1778 Enable the restartable sequences system call. It provides a
1779 user-space cache for the current CPU number value, which
1780 speeds up getting the current CPU number from user-space,
1781 as well as an ABI to speed up user-space operations on
1788 bool "Enabled debugging of rseq() system call" if EXPERT
1789 depends on RSEQ && DEBUG_KERNEL
1791 Enable extra debugging checks for the rseq system call.
1796 bool "Embedded system"
1799 This option should be enabled if compiling the kernel for
1800 an embedded system so certain expert options are available
1803 config HAVE_PERF_EVENTS
1806 See tools/perf/design.txt for details.
1808 config GUEST_PERF_EVENTS
1810 depends on HAVE_PERF_EVENTS
1812 config PERF_USE_VMALLOC
1815 See tools/perf/design.txt for details
1818 bool "PC/104 support" if EXPERT
1820 Expose PC/104 form factor device drivers and options available for
1821 selection and configuration. Enable this option if your target
1822 machine has a PC/104 bus.
1824 menu "Kernel Performance Events And Counters"
1827 bool "Kernel performance events and counters"
1828 default y if PROFILING
1829 depends on HAVE_PERF_EVENTS
1833 Enable kernel support for various performance events provided
1834 by software and hardware.
1836 Software events are supported either built-in or via the
1837 use of generic tracepoints.
1839 Most modern CPUs support performance events via performance
1840 counter registers. These registers count the number of certain
1841 types of hw events: such as instructions executed, cachemisses
1842 suffered, or branches mis-predicted - without slowing down the
1843 kernel or applications. These registers can also trigger interrupts
1844 when a threshold number of events have passed - and can thus be
1845 used to profile the code that runs on that CPU.
1847 The Linux Performance Event subsystem provides an abstraction of
1848 these software and hardware event capabilities, available via a
1849 system call and used by the "perf" utility in tools/perf/. It
1850 provides per task and per CPU counters, and it provides event
1851 capabilities on top of those.
1855 config DEBUG_PERF_USE_VMALLOC
1857 bool "Debug: use vmalloc to back perf mmap() buffers"
1858 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1859 select PERF_USE_VMALLOC
1861 Use vmalloc memory to back perf mmap() buffers.
1863 Mostly useful for debugging the vmalloc code on platforms
1864 that don't require it.
1870 config VM_EVENT_COUNTERS
1872 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1874 VM event counters are needed for event counts to be shown.
1875 This option allows the disabling of the VM event counters
1876 on EXPERT systems. /proc/vmstat will only show page counts
1877 if VM event counters are disabled.
1881 bool "Enable SLUB debugging support" if EXPERT
1882 depends on SLUB && SYSFS
1884 SLUB has extensive debug support features. Disabling these can
1885 result in significant savings in code size. This also disables
1886 SLUB sysfs support. /sys/slab will not exist and there will be
1887 no support for cache validation etc.
1890 bool "Disable heap randomization"
1893 Randomizing heap placement makes heap exploits harder, but it
1894 also breaks ancient binaries (including anything libc5 based).
1895 This option changes the bootup default to heap randomization
1896 disabled, and can be overridden at runtime by setting
1897 /proc/sys/kernel/randomize_va_space to 2.
1899 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1902 prompt "Choose SLAB allocator"
1905 This option allows to select a slab allocator.
1909 depends on !PREEMPT_RT
1910 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1912 The regular slab allocator that is established and known to work
1913 well in all environments. It organizes cache hot objects in
1914 per cpu and per node queues.
1917 bool "SLUB (Unqueued Allocator)"
1918 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1920 SLUB is a slab allocator that minimizes cache line usage
1921 instead of managing queues of cached objects (SLAB approach).
1922 Per cpu caching is realized using slabs of objects instead
1923 of queues of objects. SLUB can use memory efficiently
1924 and has enhanced diagnostics. SLUB is the default choice for
1929 bool "SLOB (Simple Allocator)"
1930 depends on !PREEMPT_RT
1932 SLOB replaces the stock allocator with a drastically simpler
1933 allocator. SLOB is generally more space efficient but
1934 does not perform as well on large systems.
1938 config SLAB_MERGE_DEFAULT
1939 bool "Allow slab caches to be merged"
1941 depends on SLAB || SLUB
1943 For reduced kernel memory fragmentation, slab caches can be
1944 merged when they share the same size and other characteristics.
1945 This carries a risk of kernel heap overflows being able to
1946 overwrite objects from merged caches (and more easily control
1947 cache layout), which makes such heap attacks easier to exploit
1948 by attackers. By keeping caches unmerged, these kinds of exploits
1949 can usually only damage objects in the same cache. To disable
1950 merging at runtime, "slab_nomerge" can be passed on the kernel
1953 config SLAB_FREELIST_RANDOM
1954 bool "Randomize slab freelist"
1955 depends on SLAB || SLUB
1957 Randomizes the freelist order used on creating new pages. This
1958 security feature reduces the predictability of the kernel slab
1959 allocator against heap overflows.
1961 config SLAB_FREELIST_HARDENED
1962 bool "Harden slab freelist metadata"
1963 depends on SLAB || SLUB
1965 Many kernel heap attacks try to target slab cache metadata and
1966 other infrastructure. This options makes minor performance
1967 sacrifices to harden the kernel slab allocator against common
1968 freelist exploit methods. Some slab implementations have more
1969 sanity-checking than others. This option is most effective with
1972 config SHUFFLE_PAGE_ALLOCATOR
1973 bool "Page allocator randomization"
1974 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1976 Randomization of the page allocator improves the average
1977 utilization of a direct-mapped memory-side-cache. See section
1978 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1979 6.2a specification for an example of how a platform advertises
1980 the presence of a memory-side-cache. There are also incidental
1981 security benefits as it reduces the predictability of page
1982 allocations to compliment SLAB_FREELIST_RANDOM, but the
1983 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1984 10th order of pages is selected based on cache utilization
1987 While the randomization improves cache utilization it may
1988 negatively impact workloads on platforms without a cache. For
1989 this reason, by default, the randomization is enabled only
1990 after runtime detection of a direct-mapped memory-side-cache.
1991 Otherwise, the randomization may be force enabled with the
1992 'page_alloc.shuffle' kernel command line parameter.
1996 config SLUB_CPU_PARTIAL
1998 depends on SLUB && SMP
1999 bool "SLUB per cpu partial cache"
2001 Per cpu partial caches accelerate objects allocation and freeing
2002 that is local to a processor at the price of more indeterminism
2003 in the latency of the free. On overflow these caches will be cleared
2004 which requires the taking of locks that may cause latency spikes.
2005 Typically one would choose no for a realtime system.
2007 config MMAP_ALLOW_UNINITIALIZED
2008 bool "Allow mmapped anonymous memory to be uninitialized"
2009 depends on EXPERT && !MMU
2012 Normally, and according to the Linux spec, anonymous memory obtained
2013 from mmap() has its contents cleared before it is passed to
2014 userspace. Enabling this config option allows you to request that
2015 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
2016 providing a huge performance boost. If this option is not enabled,
2017 then the flag will be ignored.
2019 This is taken advantage of by uClibc's malloc(), and also by
2020 ELF-FDPIC binfmt's brk and stack allocator.
2022 Because of the obvious security issues, this option should only be
2023 enabled on embedded devices where you control what is run in
2024 userspace. Since that isn't generally a problem on no-MMU systems,
2025 it is normally safe to say Y here.
2027 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
2029 config SYSTEM_DATA_VERIFICATION
2031 select SYSTEM_TRUSTED_KEYRING
2035 select ASYMMETRIC_KEY_TYPE
2036 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
2039 select X509_CERTIFICATE_PARSER
2040 select PKCS7_MESSAGE_PARSER
2042 Provide PKCS#7 message verification using the contents of the system
2043 trusted keyring to provide public keys. This then can be used for
2044 module verification, kexec image verification and firmware blob
2048 bool "Profiling support"
2050 Say Y here to enable the extended profiling support mechanisms used
2054 # Place an empty function call at each tracepoint site. Can be
2055 # dynamically changed for a probe function.
2060 endmenu # General setup
2062 source "arch/Kconfig"
2066 default y if PREEMPT_RT
2070 default 0 if BASE_FULL
2071 default 1 if !BASE_FULL
2073 config MODULE_SIG_FORMAT
2075 select SYSTEM_DATA_VERIFICATION
2078 bool "Enable loadable module support"
2081 Kernel modules are small pieces of compiled code which can
2082 be inserted in the running kernel, rather than being
2083 permanently built into the kernel. You use the "modprobe"
2084 tool to add (and sometimes remove) them. If you say Y here,
2085 many parts of the kernel can be built as modules (by
2086 answering M instead of Y where indicated): this is most
2087 useful for infrequently used options which are not required
2088 for booting. For more information, see the man pages for
2089 modprobe, lsmod, modinfo, insmod and rmmod.
2091 If you say Y here, you will need to run "make
2092 modules_install" to put the modules under /lib/modules/
2093 where modprobe can find them (you may need to be root to do
2100 config MODULE_FORCE_LOAD
2101 bool "Forced module loading"
2104 Allow loading of modules without version information (ie. modprobe
2105 --force). Forced module loading sets the 'F' (forced) taint flag and
2106 is usually a really bad idea.
2108 config MODULE_UNLOAD
2109 bool "Module unloading"
2111 Without this option you will not be able to unload any
2112 modules (note that some modules may not be unloadable
2113 anyway), which makes your kernel smaller, faster
2114 and simpler. If unsure, say Y.
2116 config MODULE_FORCE_UNLOAD
2117 bool "Forced module unloading"
2118 depends on MODULE_UNLOAD
2120 This option allows you to force a module to unload, even if the
2121 kernel believes it is unsafe: the kernel will remove the module
2122 without waiting for anyone to stop using it (using the -f option to
2123 rmmod). This is mainly for kernel developers and desperate users.
2127 bool "Module versioning support"
2129 Usually, you have to use modules compiled with your kernel.
2130 Saying Y here makes it sometimes possible to use modules
2131 compiled for different kernels, by adding enough information
2132 to the modules to (hopefully) spot any changes which would
2133 make them incompatible with the kernel you are running. If
2136 config ASM_MODVERSIONS
2138 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2140 This enables module versioning for exported symbols also from
2141 assembly. This can be enabled only when the target architecture
2144 config MODULE_REL_CRCS
2146 depends on MODVERSIONS
2148 config MODULE_SRCVERSION_ALL
2149 bool "Source checksum for all modules"
2151 Modules which contain a MODULE_VERSION get an extra "srcversion"
2152 field inserted into their modinfo section, which contains a
2153 sum of the source files which made it. This helps maintainers
2154 see exactly which source was used to build a module (since
2155 others sometimes change the module source without updating
2156 the version). With this option, such a "srcversion" field
2157 will be created for all modules. If unsure, say N.
2160 bool "Module signature verification"
2161 select MODULE_SIG_FORMAT
2163 Check modules for valid signatures upon load: the signature
2164 is simply appended to the module. For more information see
2165 <file:Documentation/admin-guide/module-signing.rst>.
2167 Note that this option adds the OpenSSL development packages as a
2168 kernel build dependency so that the signing tool can use its crypto
2171 You should enable this option if you wish to use either
2172 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2173 another LSM - otherwise unsigned modules will be loadable regardless
2174 of the lockdown policy.
2176 !!!WARNING!!! If you enable this option, you MUST make sure that the
2177 module DOES NOT get stripped after being signed. This includes the
2178 debuginfo strip done by some packagers (such as rpmbuild) and
2179 inclusion into an initramfs that wants the module size reduced.
2181 config MODULE_SIG_FORCE
2182 bool "Require modules to be validly signed"
2183 depends on MODULE_SIG
2185 Reject unsigned modules or signed modules for which we don't have a
2186 key. Without this, such modules will simply taint the kernel.
2188 config MODULE_SIG_ALL
2189 bool "Automatically sign all modules"
2191 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2193 Sign all modules during make modules_install. Without this option,
2194 modules must be signed manually, using the scripts/sign-file tool.
2196 comment "Do not forget to sign required modules with scripts/sign-file"
2197 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2200 prompt "Which hash algorithm should modules be signed with?"
2201 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2203 This determines which sort of hashing algorithm will be used during
2204 signature generation. This algorithm _must_ be built into the kernel
2205 directly so that signature verification can take place. It is not
2206 possible to load a signed module containing the algorithm to check
2207 the signature on that module.
2209 config MODULE_SIG_SHA1
2210 bool "Sign modules with SHA-1"
2213 config MODULE_SIG_SHA224
2214 bool "Sign modules with SHA-224"
2215 select CRYPTO_SHA256
2217 config MODULE_SIG_SHA256
2218 bool "Sign modules with SHA-256"
2219 select CRYPTO_SHA256
2221 config MODULE_SIG_SHA384
2222 bool "Sign modules with SHA-384"
2223 select CRYPTO_SHA512
2225 config MODULE_SIG_SHA512
2226 bool "Sign modules with SHA-512"
2227 select CRYPTO_SHA512
2231 config MODULE_SIG_HASH
2233 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2234 default "sha1" if MODULE_SIG_SHA1
2235 default "sha224" if MODULE_SIG_SHA224
2236 default "sha256" if MODULE_SIG_SHA256
2237 default "sha384" if MODULE_SIG_SHA384
2238 default "sha512" if MODULE_SIG_SHA512
2241 prompt "Module compression mode"
2243 This option allows you to choose the algorithm which will be used to
2244 compress modules when 'make modules_install' is run. (or, you can
2245 choose to not compress modules at all.)
2247 External modules will also be compressed in the same way during the
2250 For modules inside an initrd or initramfs, it's more efficient to
2251 compress the whole initrd or initramfs instead.
2253 This is fully compatible with signed modules.
2255 Please note that the tool used to load modules needs to support the
2256 corresponding algorithm. module-init-tools MAY support gzip, and kmod
2257 MAY support gzip, xz and zstd.
2259 Your build system needs to provide the appropriate compression tool
2260 to compress the modules.
2262 If in doubt, select 'None'.
2264 config MODULE_COMPRESS_NONE
2267 Do not compress modules. The installed modules are suffixed
2270 config MODULE_COMPRESS_GZIP
2273 Compress modules with GZIP. The installed modules are suffixed
2276 config MODULE_COMPRESS_XZ
2279 Compress modules with XZ. The installed modules are suffixed
2282 config MODULE_COMPRESS_ZSTD
2285 Compress modules with ZSTD. The installed modules are suffixed
2290 config MODULE_DECOMPRESS
2291 bool "Support in-kernel module decompression"
2292 depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
2293 select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
2294 select XZ_DEC if MODULE_COMPRESS_XZ
2297 Support for decompressing kernel modules by the kernel itself
2298 instead of relying on userspace to perform this task. Useful when
2299 load pinning security policy is enabled.
2303 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2304 bool "Allow loading of modules with missing namespace imports"
2306 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2307 a namespace. A module that makes use of a symbol exported with such a
2308 namespace is required to import the namespace via MODULE_IMPORT_NS().
2309 There is no technical reason to enforce correct namespace imports,
2310 but it creates consistency between symbols defining namespaces and
2311 users importing namespaces they make use of. This option relaxes this
2312 requirement and lifts the enforcement when loading a module.
2316 config MODPROBE_PATH
2317 string "Path to modprobe binary"
2318 default "/sbin/modprobe"
2320 When kernel code requests a module, it does so by calling
2321 the "modprobe" userspace utility. This option allows you to
2322 set the path where that binary is found. This can be changed
2323 at runtime via the sysctl file
2324 /proc/sys/kernel/modprobe. Setting this to the empty string
2325 removes the kernel's ability to request modules (but
2326 userspace can still load modules explicitly).
2328 config TRIM_UNUSED_KSYMS
2329 bool "Trim unused exported kernel symbols" if EXPERT
2330 depends on !COMPILE_TEST
2332 The kernel and some modules make many symbols available for
2333 other modules to use via EXPORT_SYMBOL() and variants. Depending
2334 on the set of modules being selected in your kernel configuration,
2335 many of those exported symbols might never be used.
2337 This option allows for unused exported symbols to be dropped from
2338 the build. In turn, this provides the compiler more opportunities
2339 (especially when using LTO) for optimizing the code and reducing
2340 binary size. This might have some security advantages as well.
2342 If unsure, or if you need to build out-of-tree modules, say N.
2344 config UNUSED_KSYMS_WHITELIST
2345 string "Whitelist of symbols to keep in ksymtab"
2346 depends on TRIM_UNUSED_KSYMS
2348 By default, all unused exported symbols will be un-exported from the
2349 build when TRIM_UNUSED_KSYMS is selected.
2351 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2352 exported at all times, even in absence of in-tree users. The value to
2353 set here is the path to a text file containing the list of symbols,
2354 one per line. The path can be absolute, or relative to the kernel
2359 config MODULES_TREE_LOOKUP
2361 depends on PERF_EVENTS || TRACING || CFI_CLANG
2363 config INIT_ALL_POSSIBLE
2366 Back when each arch used to define their own cpu_online_mask and
2367 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2368 with all 1s, and others with all 0s. When they were centralised,
2369 it was better to provide this option than to break all the archs
2370 and have several arch maintainers pursuing me down dark alleys.
2372 source "block/Kconfig"
2374 config PREEMPT_NOTIFIERS
2384 Build a simple ASN.1 grammar compiler that produces a bytecode output
2385 that can be interpreted by the ASN.1 stream decoder and used to
2386 inform it as to what tags are to be expected in a stream and what
2387 functions to call on what tags.
2389 source "kernel/Kconfig.locks"
2391 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2394 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2397 # It may be useful for an architecture to override the definitions of the
2398 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2399 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2400 # different calling convention for syscalls. They can also override the
2401 # macros for not-implemented syscalls in kernel/sys_ni.c and
2402 # kernel/time/posix-stubs.c. All these overrides need to be available in
2403 # <asm/syscall_wrapper.h>.
2404 config ARCH_HAS_SYSCALL_WRAPPER
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