7 option env="KERNELVERSION"
13 default "/lib/modules/$UNAME_RELEASE/.config"
14 default "/etc/kernel-config"
15 default "/boot/config-$UNAME_RELEASE"
16 default "$ARCH_DEFCONFIG"
17 default "arch/$ARCH/defconfig"
26 config BUILDTIME_EXTABLE_SORT
29 config THREAD_INFO_IN_TASK
32 Select this to move thread_info off the stack into task_struct. To
33 make this work, an arch will need to remove all thread_info fields
34 except flags and fix any runtime bugs.
36 One subtle change that will be needed is to use try_get_task_stack()
37 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
46 depends on BROKEN || !SMP
49 config INIT_ENV_ARG_LIMIT
54 Maximum of each of the number of arguments and environment
55 variables passed to init from the kernel command line.
59 string "Cross-compiler tool prefix"
61 Same as running 'make CROSS_COMPILE=prefix-' but stored for
62 default make runs in this kernel build directory. You don't
63 need to set this unless you want the configured kernel build
64 directory to select the cross-compiler automatically.
67 bool "Compile also drivers which will not load"
71 Some drivers can be compiled on a different platform than they are
72 intended to be run on. Despite they cannot be loaded there (or even
73 when they load they cannot be used due to missing HW support),
74 developers still, opposing to distributors, might want to build such
75 drivers to compile-test them.
77 If you are a developer and want to build everything available, say Y
78 here. If you are a user/distributor, say N here to exclude useless
79 drivers to be distributed.
82 string "Local version - append to kernel release"
84 Append an extra string to the end of your kernel version.
85 This will show up when you type uname, for example.
86 The string you set here will be appended after the contents of
87 any files with a filename matching localversion* in your
88 object and source tree, in that order. Your total string can
89 be a maximum of 64 characters.
91 config LOCALVERSION_AUTO
92 bool "Automatically append version information to the version string"
94 depends on !COMPILE_TEST
96 This will try to automatically determine if the current tree is a
97 release tree by looking for git tags that belong to the current
100 A string of the format -gxxxxxxxx will be added to the localversion
101 if a git-based tree is found. The string generated by this will be
102 appended after any matching localversion* files, and after the value
103 set in CONFIG_LOCALVERSION.
105 (The actual string used here is the first eight characters produced
106 by running the command:
108 $ git rev-parse --verify HEAD
110 which is done within the script "scripts/setlocalversion".)
112 config HAVE_KERNEL_GZIP
115 config HAVE_KERNEL_BZIP2
118 config HAVE_KERNEL_LZMA
121 config HAVE_KERNEL_XZ
124 config HAVE_KERNEL_LZO
127 config HAVE_KERNEL_LZ4
131 prompt "Kernel compression mode"
133 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
135 The linux kernel is a kind of self-extracting executable.
136 Several compression algorithms are available, which differ
137 in efficiency, compression and decompression speed.
138 Compression speed is only relevant when building a kernel.
139 Decompression speed is relevant at each boot.
141 If you have any problems with bzip2 or lzma compressed
142 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
143 version of this functionality (bzip2 only), for 2.4, was
144 supplied by Christian Ludwig)
146 High compression options are mostly useful for users, who
147 are low on disk space (embedded systems), but for whom ram
150 If in doubt, select 'gzip'
154 depends on HAVE_KERNEL_GZIP
156 The old and tried gzip compression. It provides a good balance
157 between compression ratio and decompression speed.
161 depends on HAVE_KERNEL_BZIP2
163 Its compression ratio and speed is intermediate.
164 Decompression speed is slowest among the choices. The kernel
165 size is about 10% smaller with bzip2, in comparison to gzip.
166 Bzip2 uses a large amount of memory. For modern kernels you
167 will need at least 8MB RAM or more for booting.
171 depends on HAVE_KERNEL_LZMA
173 This compression algorithm's ratio is best. Decompression speed
174 is between gzip and bzip2. Compression is slowest.
175 The kernel size is about 33% smaller with LZMA in comparison to gzip.
179 depends on HAVE_KERNEL_XZ
181 XZ uses the LZMA2 algorithm and instruction set specific
182 BCJ filters which can improve compression ratio of executable
183 code. The size of the kernel is about 30% smaller with XZ in
184 comparison to gzip. On architectures for which there is a BCJ
185 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
186 will create a few percent smaller kernel than plain LZMA.
188 The speed is about the same as with LZMA: The decompression
189 speed of XZ is better than that of bzip2 but worse than gzip
190 and LZO. Compression is slow.
194 depends on HAVE_KERNEL_LZO
196 Its compression ratio is the poorest among the choices. The kernel
197 size is about 10% bigger than gzip; however its speed
198 (both compression and decompression) is the fastest.
202 depends on HAVE_KERNEL_LZ4
204 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
205 A preliminary version of LZ4 de/compression tool is available at
206 <https://code.google.com/p/lz4/>.
208 Its compression ratio is worse than LZO. The size of the kernel
209 is about 8% bigger than LZO. But the decompression speed is
214 config DEFAULT_HOSTNAME
215 string "Default hostname"
218 This option determines the default system hostname before userspace
219 calls sethostname(2). The kernel traditionally uses "(none)" here,
220 but you may wish to use a different default here to make a minimal
221 system more usable with less configuration.
224 bool "Support for paging of anonymous memory (swap)"
225 depends on MMU && BLOCK
228 This option allows you to choose whether you want to have support
229 for so called swap devices or swap files in your kernel that are
230 used to provide more virtual memory than the actual RAM present
231 in your computer. If unsure say Y.
236 Inter Process Communication is a suite of library functions and
237 system calls which let processes (running programs) synchronize and
238 exchange information. It is generally considered to be a good thing,
239 and some programs won't run unless you say Y here. In particular, if
240 you want to run the DOS emulator dosemu under Linux (read the
241 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
242 you'll need to say Y here.
244 You can find documentation about IPC with "info ipc" and also in
245 section 6.4 of the Linux Programmer's Guide, available from
246 <http://www.tldp.org/guides.html>.
248 config SYSVIPC_SYSCTL
255 bool "POSIX Message Queues"
258 POSIX variant of message queues is a part of IPC. In POSIX message
259 queues every message has a priority which decides about succession
260 of receiving it by a process. If you want to compile and run
261 programs written e.g. for Solaris with use of its POSIX message
262 queues (functions mq_*) say Y here.
264 POSIX message queues are visible as a filesystem called 'mqueue'
265 and can be mounted somewhere if you want to do filesystem
266 operations on message queues.
270 config POSIX_MQUEUE_SYSCTL
272 depends on POSIX_MQUEUE
276 config CROSS_MEMORY_ATTACH
277 bool "Enable process_vm_readv/writev syscalls"
281 Enabling this option adds the system calls process_vm_readv and
282 process_vm_writev which allow a process with the correct privileges
283 to directly read from or write to another process' address space.
284 See the man page for more details.
287 bool "open by fhandle syscalls" if EXPERT
291 If you say Y here, a user level program will be able to map
292 file names to handle and then later use the handle for
293 different file system operations. This is useful in implementing
294 userspace file servers, which now track files using handles instead
295 of names. The handle would remain the same even if file names
296 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
300 bool "uselib syscall"
301 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
303 This option enables the uselib syscall, a system call used in the
304 dynamic linker from libc5 and earlier. glibc does not use this
305 system call. If you intend to run programs built on libc5 or
306 earlier, you may need to enable this syscall. Current systems
307 running glibc can safely disable this.
310 bool "Auditing support"
313 Enable auditing infrastructure that can be used with another
314 kernel subsystem, such as SELinux (which requires this for
315 logging of avc messages output). System call auditing is included
316 on architectures which support it.
318 config HAVE_ARCH_AUDITSYSCALL
323 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
327 depends on AUDITSYSCALL
332 depends on AUDITSYSCALL
335 source "kernel/irq/Kconfig"
336 source "kernel/time/Kconfig"
338 menu "CPU/Task time and stats accounting"
340 config VIRT_CPU_ACCOUNTING
344 prompt "Cputime accounting"
345 default TICK_CPU_ACCOUNTING if !PPC64
346 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
348 # Kind of a stub config for the pure tick based cputime accounting
349 config TICK_CPU_ACCOUNTING
350 bool "Simple tick based cputime accounting"
351 depends on !S390 && !NO_HZ_FULL
353 This is the basic tick based cputime accounting that maintains
354 statistics about user, system and idle time spent on per jiffies
359 config VIRT_CPU_ACCOUNTING_NATIVE
360 bool "Deterministic task and CPU time accounting"
361 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
362 select VIRT_CPU_ACCOUNTING
364 Select this option to enable more accurate task and CPU time
365 accounting. This is done by reading a CPU counter on each
366 kernel entry and exit and on transitions within the kernel
367 between system, softirq and hardirq state, so there is a
368 small performance impact. In the case of s390 or IBM POWER > 5,
369 this also enables accounting of stolen time on logically-partitioned
372 config VIRT_CPU_ACCOUNTING_GEN
373 bool "Full dynticks CPU time accounting"
374 depends on HAVE_CONTEXT_TRACKING
375 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
376 select VIRT_CPU_ACCOUNTING
377 select CONTEXT_TRACKING
379 Select this option to enable task and CPU time accounting on full
380 dynticks systems. This accounting is implemented by watching every
381 kernel-user boundaries using the context tracking subsystem.
382 The accounting is thus performed at the expense of some significant
385 For now this is only useful if you are working on the full
386 dynticks subsystem development.
392 config IRQ_TIME_ACCOUNTING
393 bool "Fine granularity task level IRQ time accounting"
394 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
396 Select this option to enable fine granularity task irq time
397 accounting. This is done by reading a timestamp on each
398 transitions between softirq and hardirq state, so there can be a
399 small performance impact.
401 If in doubt, say N here.
403 config BSD_PROCESS_ACCT
404 bool "BSD Process Accounting"
407 If you say Y here, a user level program will be able to instruct the
408 kernel (via a special system call) to write process accounting
409 information to a file: whenever a process exits, information about
410 that process will be appended to the file by the kernel. The
411 information includes things such as creation time, owning user,
412 command name, memory usage, controlling terminal etc. (the complete
413 list is in the struct acct in <file:include/linux/acct.h>). It is
414 up to the user level program to do useful things with this
415 information. This is generally a good idea, so say Y.
417 config BSD_PROCESS_ACCT_V3
418 bool "BSD Process Accounting version 3 file format"
419 depends on BSD_PROCESS_ACCT
422 If you say Y here, the process accounting information is written
423 in a new file format that also logs the process IDs of each
424 process and it's parent. Note that this file format is incompatible
425 with previous v0/v1/v2 file formats, so you will need updated tools
426 for processing it. A preliminary version of these tools is available
427 at <http://www.gnu.org/software/acct/>.
430 bool "Export task/process statistics through netlink"
435 Export selected statistics for tasks/processes through the
436 generic netlink interface. Unlike BSD process accounting, the
437 statistics are available during the lifetime of tasks/processes as
438 responses to commands. Like BSD accounting, they are sent to user
443 config TASK_DELAY_ACCT
444 bool "Enable per-task delay accounting"
448 Collect information on time spent by a task waiting for system
449 resources like cpu, synchronous block I/O completion and swapping
450 in pages. Such statistics can help in setting a task's priorities
451 relative to other tasks for cpu, io, rss limits etc.
456 bool "Enable extended accounting over taskstats"
459 Collect extended task accounting data and send the data
460 to userland for processing over the taskstats interface.
464 config TASK_IO_ACCOUNTING
465 bool "Enable per-task storage I/O accounting"
466 depends on TASK_XACCT
468 Collect information on the number of bytes of storage I/O which this
473 endmenu # "CPU/Task time and stats accounting"
479 default y if !PREEMPT && SMP
481 This option selects the RCU implementation that is
482 designed for very large SMP system with hundreds or
483 thousands of CPUs. It also scales down nicely to
490 This option selects the RCU implementation that is
491 designed for very large SMP systems with hundreds or
492 thousands of CPUs, but for which real-time response
493 is also required. It also scales down nicely to
496 Select this option if you are unsure.
500 default y if !PREEMPT && !SMP
502 This option selects the RCU implementation that is
503 designed for UP systems from which real-time response
504 is not required. This option greatly reduces the
505 memory footprint of RCU.
508 bool "Make expert-level adjustments to RCU configuration"
511 This option needs to be enabled if you wish to make
512 expert-level adjustments to RCU configuration. By default,
513 no such adjustments can be made, which has the often-beneficial
514 side-effect of preventing "make oldconfig" from asking you all
515 sorts of detailed questions about how you would like numerous
516 obscure RCU options to be set up.
518 Say Y if you need to make expert-level adjustments to RCU.
520 Say N if you are unsure.
526 This option selects the sleepable version of RCU. This version
527 permits arbitrary sleeping or blocking within RCU read-side critical
531 bool "Use v4.11 classic SRCU implementation"
533 depends on RCU_EXPERT && SRCU
535 This option selects the traditional well-tested classic SRCU
536 implementation from v4.11, as might be desired for enterprise
537 Linux distributions. Without this option, the shiny new
538 Tiny SRCU and Tree SRCU implementations are used instead.
539 At some point, it is hoped that Tiny SRCU and Tree SRCU
540 will accumulate enough test time and confidence to allow
541 Classic SRCU to be dropped entirely.
543 Say Y if you need a rock-solid SRCU.
545 Say N if you would like help test Tree SRCU.
549 default y if SRCU && TINY_RCU && !CLASSIC_SRCU
551 This option selects the single-CPU non-preemptible version of SRCU.
555 default y if SRCU && !TINY_RCU && !CLASSIC_SRCU
557 This option selects the full-fledged version of SRCU.
564 This option enables a task-based RCU implementation that uses
565 only voluntary context switch (not preemption!), idle, and
566 user-mode execution as quiescent states.
568 config RCU_STALL_COMMON
569 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
571 This option enables RCU CPU stall code that is common between
572 the TINY and TREE variants of RCU. The purpose is to allow
573 the tiny variants to disable RCU CPU stall warnings, while
574 making these warnings mandatory for the tree variants.
576 config RCU_NEED_SEGCBLIST
577 def_bool ( TREE_RCU || PREEMPT_RCU || TINY_SRCU || TREE_SRCU )
579 config CONTEXT_TRACKING
582 config CONTEXT_TRACKING_FORCE
583 bool "Force context tracking"
584 depends on CONTEXT_TRACKING
585 default y if !NO_HZ_FULL
587 The major pre-requirement for full dynticks to work is to
588 support the context tracking subsystem. But there are also
589 other dependencies to provide in order to make the full
592 This option stands for testing when an arch implements the
593 context tracking backend but doesn't yet fullfill all the
594 requirements to make the full dynticks feature working.
595 Without the full dynticks, there is no way to test the support
596 for context tracking and the subsystems that rely on it: RCU
597 userspace extended quiescent state and tickless cputime
598 accounting. This option copes with the absence of the full
599 dynticks subsystem by forcing the context tracking on all
602 Say Y only if you're working on the development of an
603 architecture backend for the context tracking.
605 Say N otherwise, this option brings an overhead that you
606 don't want in production.
610 int "Tree-based hierarchical RCU fanout value"
613 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
617 This option controls the fanout of hierarchical implementations
618 of RCU, allowing RCU to work efficiently on machines with
619 large numbers of CPUs. This value must be at least the fourth
620 root of NR_CPUS, which allows NR_CPUS to be insanely large.
621 The default value of RCU_FANOUT should be used for production
622 systems, but if you are stress-testing the RCU implementation
623 itself, small RCU_FANOUT values allow you to test large-system
624 code paths on small(er) systems.
626 Select a specific number if testing RCU itself.
627 Take the default if unsure.
629 config RCU_FANOUT_LEAF
630 int "Tree-based hierarchical RCU leaf-level fanout value"
633 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
636 This option controls the leaf-level fanout of hierarchical
637 implementations of RCU, and allows trading off cache misses
638 against lock contention. Systems that synchronize their
639 scheduling-clock interrupts for energy-efficiency reasons will
640 want the default because the smaller leaf-level fanout keeps
641 lock contention levels acceptably low. Very large systems
642 (hundreds or thousands of CPUs) will instead want to set this
643 value to the maximum value possible in order to reduce the
644 number of cache misses incurred during RCU's grace-period
645 initialization. These systems tend to run CPU-bound, and thus
646 are not helped by synchronized interrupts, and thus tend to
647 skew them, which reduces lock contention enough that large
648 leaf-level fanouts work well. That said, setting leaf-level
649 fanout to a large number will likely cause problematic
650 lock contention on the leaf-level rcu_node structures unless
651 you boot with the skew_tick kernel parameter.
653 Select a specific number if testing RCU itself.
655 Select the maximum permissible value for large systems, but
656 please understand that you may also need to set the skew_tick
657 kernel boot parameter to avoid contention on the rcu_node
660 Take the default if unsure.
662 config RCU_FAST_NO_HZ
663 bool "Accelerate last non-dyntick-idle CPU's grace periods"
664 depends on NO_HZ_COMMON && SMP && RCU_EXPERT
667 This option permits CPUs to enter dynticks-idle state even if
668 they have RCU callbacks queued, and prevents RCU from waking
669 these CPUs up more than roughly once every four jiffies (by
670 default, you can adjust this using the rcutree.rcu_idle_gp_delay
671 parameter), thus improving energy efficiency. On the other
672 hand, this option increases the duration of RCU grace periods,
673 for example, slowing down synchronize_rcu().
675 Say Y if energy efficiency is critically important, and you
676 don't care about increased grace-period durations.
678 Say N if you are unsure.
680 config TREE_RCU_TRACE
681 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
684 This option provides tracing for the TREE_RCU and
685 PREEMPT_RCU implementations, permitting Makefile to
686 trivially select kernel/rcutree_trace.c.
689 bool "Enable RCU priority boosting"
690 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
693 This option boosts the priority of preempted RCU readers that
694 block the current preemptible RCU grace period for too long.
695 This option also prevents heavy loads from blocking RCU
696 callback invocation for all flavors of RCU.
698 Say Y here if you are working with real-time apps or heavy loads
699 Say N here if you are unsure.
701 config RCU_KTHREAD_PRIO
702 int "Real-time priority to use for RCU worker threads"
703 range 1 99 if RCU_BOOST
704 range 0 99 if !RCU_BOOST
705 default 1 if RCU_BOOST
706 default 0 if !RCU_BOOST
707 depends on RCU_EXPERT
709 This option specifies the SCHED_FIFO priority value that will be
710 assigned to the rcuc/n and rcub/n threads and is also the value
711 used for RCU_BOOST (if enabled). If you are working with a
712 real-time application that has one or more CPU-bound threads
713 running at a real-time priority level, you should set
714 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
715 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
716 value of 1 is appropriate in the common case, which is real-time
717 applications that do not have any CPU-bound threads.
719 Some real-time applications might not have a single real-time
720 thread that saturates a given CPU, but instead might have
721 multiple real-time threads that, taken together, fully utilize
722 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
723 a priority higher than the lowest-priority thread that is
724 conspiring to prevent the CPU from running any non-real-time
725 tasks. For example, if one thread at priority 10 and another
726 thread at priority 5 are between themselves fully consuming
727 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
728 set to priority 6 or higher.
730 Specify the real-time priority, or take the default if unsure.
732 config RCU_BOOST_DELAY
733 int "Milliseconds to delay boosting after RCU grace-period start"
738 This option specifies the time to wait after the beginning of
739 a given grace period before priority-boosting preempted RCU
740 readers blocking that grace period. Note that any RCU reader
741 blocking an expedited RCU grace period is boosted immediately.
743 Accept the default if unsure.
746 bool "Offload RCU callback processing from boot-selected CPUs"
747 depends on TREE_RCU || PREEMPT_RCU
748 depends on RCU_EXPERT || NO_HZ_FULL
751 Use this option to reduce OS jitter for aggressive HPC or
752 real-time workloads. It can also be used to offload RCU
753 callback invocation to energy-efficient CPUs in battery-powered
754 asymmetric multiprocessors.
756 This option offloads callback invocation from the set of
757 CPUs specified at boot time by the rcu_nocbs parameter.
758 For each such CPU, a kthread ("rcuox/N") will be created to
759 invoke callbacks, where the "N" is the CPU being offloaded,
760 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
761 "s" for RCU-sched. Nothing prevents this kthread from running
762 on the specified CPUs, but (1) the kthreads may be preempted
763 between each callback, and (2) affinity or cgroups can be used
764 to force the kthreads to run on whatever set of CPUs is desired.
766 Say Y here if you want to help to debug reduced OS jitter.
767 Say N here if you are unsure.
770 prompt "Build-forced no-CBs CPUs"
771 default RCU_NOCB_CPU_NONE
772 depends on RCU_NOCB_CPU
774 This option allows no-CBs CPUs (whose RCU callbacks are invoked
775 from kthreads rather than from softirq context) to be specified
776 at build time. Additional no-CBs CPUs may be specified by
777 the rcu_nocbs= boot parameter.
779 config RCU_NOCB_CPU_NONE
780 bool "No build_forced no-CBs CPUs"
782 This option does not force any of the CPUs to be no-CBs CPUs.
783 Only CPUs designated by the rcu_nocbs= boot parameter will be
784 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
785 kthreads whose names begin with "rcuo". All other CPUs will
786 invoke their own RCU callbacks in softirq context.
788 Select this option if you want to choose no-CBs CPUs at
789 boot time, for example, to allow testing of different no-CBs
790 configurations without having to rebuild the kernel each time.
792 config RCU_NOCB_CPU_ZERO
793 bool "CPU 0 is a build_forced no-CBs CPU"
795 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
796 callbacks are invoked by a per-CPU kthread whose name begins
797 with "rcuo". Additional CPUs may be designated as no-CBs
798 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
799 All other CPUs will invoke their own RCU callbacks in softirq
802 Select this if CPU 0 needs to be a no-CBs CPU for real-time
803 or energy-efficiency reasons, but the real reason it exists
804 is to ensure that randconfig testing covers mixed systems.
806 config RCU_NOCB_CPU_ALL
807 bool "All CPUs are build_forced no-CBs CPUs"
809 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
810 boot parameter will be ignored. All CPUs' RCU callbacks will
811 be executed in the context of per-CPU rcuo kthreads created for
812 this purpose. Assuming that the kthreads whose names start with
813 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
814 on the remaining CPUs, but might decrease memory locality during
815 RCU-callback invocation, thus potentially degrading throughput.
817 Select this if all CPUs need to be no-CBs CPUs for real-time
818 or energy-efficiency reasons.
822 endmenu # "RCU Subsystem"
829 tristate "Kernel .config support"
832 This option enables the complete Linux kernel ".config" file
833 contents to be saved in the kernel. It provides documentation
834 of which kernel options are used in a running kernel or in an
835 on-disk kernel. This information can be extracted from the kernel
836 image file with the script scripts/extract-ikconfig and used as
837 input to rebuild the current kernel or to build another kernel.
838 It can also be extracted from a running kernel by reading
839 /proc/config.gz if enabled (below).
842 bool "Enable access to .config through /proc/config.gz"
843 depends on IKCONFIG && PROC_FS
845 This option enables access to the kernel configuration file
846 through /proc/config.gz.
849 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
854 Select the minimal kernel log buffer size as a power of 2.
855 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
856 parameter, see below. Any higher size also might be forced
857 by "log_buf_len" boot parameter.
867 config LOG_CPU_MAX_BUF_SHIFT
868 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
871 default 12 if !BASE_SMALL
872 default 0 if BASE_SMALL
875 This option allows to increase the default ring buffer size
876 according to the number of CPUs. The value defines the contribution
877 of each CPU as a power of 2. The used space is typically only few
878 lines however it might be much more when problems are reported,
881 The increased size means that a new buffer has to be allocated and
882 the original static one is unused. It makes sense only on systems
883 with more CPUs. Therefore this value is used only when the sum of
884 contributions is greater than the half of the default kernel ring
885 buffer as defined by LOG_BUF_SHIFT. The default values are set
886 so that more than 64 CPUs are needed to trigger the allocation.
888 Also this option is ignored when "log_buf_len" kernel parameter is
889 used as it forces an exact (power of two) size of the ring buffer.
891 The number of possible CPUs is used for this computation ignoring
892 hotplugging making the computation optimal for the worst case
893 scenario while allowing a simple algorithm to be used from bootup.
895 Examples shift values and their meaning:
896 17 => 128 KB for each CPU
897 16 => 64 KB for each CPU
898 15 => 32 KB for each CPU
899 14 => 16 KB for each CPU
900 13 => 8 KB for each CPU
901 12 => 4 KB for each CPU
903 config PRINTK_SAFE_LOG_BUF_SHIFT
904 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
909 Select the size of an alternate printk per-CPU buffer where messages
910 printed from usafe contexts are temporary stored. One example would
911 be NMI messages, another one - printk recursion. The messages are
912 copied to the main log buffer in a safe context to avoid a deadlock.
913 The value defines the size as a power of 2.
915 Those messages are rare and limited. The largest one is when
916 a backtrace is printed. It usually fits into 4KB. Select
917 8KB if you want to be on the safe side.
920 17 => 128 KB for each CPU
921 16 => 64 KB for each CPU
922 15 => 32 KB for each CPU
923 14 => 16 KB for each CPU
924 13 => 8 KB for each CPU
925 12 => 4 KB for each CPU
928 # Architectures with an unreliable sched_clock() should select this:
930 config HAVE_UNSTABLE_SCHED_CLOCK
933 config GENERIC_SCHED_CLOCK
937 # For architectures that want to enable the support for NUMA-affine scheduler
940 config ARCH_SUPPORTS_NUMA_BALANCING
944 # For architectures that prefer to flush all TLBs after a number of pages
945 # are unmapped instead of sending one IPI per page to flush. The architecture
946 # must provide guarantees on what happens if a clean TLB cache entry is
947 # written after the unmap. Details are in mm/rmap.c near the check for
948 # should_defer_flush. The architecture should also consider if the full flush
949 # and the refill costs are offset by the savings of sending fewer IPIs.
950 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
954 # For architectures that know their GCC __int128 support is sound
956 config ARCH_SUPPORTS_INT128
959 # For architectures that (ab)use NUMA to represent different memory regions
960 # all cpu-local but of different latencies, such as SuperH.
962 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
965 config NUMA_BALANCING
966 bool "Memory placement aware NUMA scheduler"
967 depends on ARCH_SUPPORTS_NUMA_BALANCING
968 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
969 depends on SMP && NUMA && MIGRATION
971 This option adds support for automatic NUMA aware memory/task placement.
972 The mechanism is quite primitive and is based on migrating memory when
973 it has references to the node the task is running on.
975 This system will be inactive on UMA systems.
977 config NUMA_BALANCING_DEFAULT_ENABLED
978 bool "Automatically enable NUMA aware memory/task placement"
980 depends on NUMA_BALANCING
982 If set, automatic NUMA balancing will be enabled if running on a NUMA
986 bool "Control Group support"
989 This option adds support for grouping sets of processes together, for
990 use with process control subsystems such as Cpusets, CFS, memory
991 controls or device isolation.
993 - Documentation/scheduler/sched-design-CFS.txt (CFS)
994 - Documentation/cgroup-v1/ (features for grouping, isolation
995 and resource control)
1005 bool "Memory controller"
1009 Provides control over the memory footprint of tasks in a cgroup.
1012 bool "Swap controller"
1013 depends on MEMCG && SWAP
1015 Provides control over the swap space consumed by tasks in a cgroup.
1017 config MEMCG_SWAP_ENABLED
1018 bool "Swap controller enabled by default"
1019 depends on MEMCG_SWAP
1022 Memory Resource Controller Swap Extension comes with its price in
1023 a bigger memory consumption. General purpose distribution kernels
1024 which want to enable the feature but keep it disabled by default
1025 and let the user enable it by swapaccount=1 boot command line
1026 parameter should have this option unselected.
1027 For those who want to have the feature enabled by default should
1028 select this option (if, for some reason, they need to disable it
1029 then swapaccount=0 does the trick).
1032 bool "IO controller"
1036 Generic block IO controller cgroup interface. This is the common
1037 cgroup interface which should be used by various IO controlling
1040 Currently, CFQ IO scheduler uses it to recognize task groups and
1041 control disk bandwidth allocation (proportional time slice allocation)
1042 to such task groups. It is also used by bio throttling logic in
1043 block layer to implement upper limit in IO rates on a device.
1045 This option only enables generic Block IO controller infrastructure.
1046 One needs to also enable actual IO controlling logic/policy. For
1047 enabling proportional weight division of disk bandwidth in CFQ, set
1048 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1049 CONFIG_BLK_DEV_THROTTLING=y.
1051 See Documentation/cgroup-v1/blkio-controller.txt for more information.
1053 config DEBUG_BLK_CGROUP
1054 bool "IO controller debugging"
1055 depends on BLK_CGROUP
1058 Enable some debugging help. Currently it exports additional stat
1059 files in a cgroup which can be useful for debugging.
1061 config CGROUP_WRITEBACK
1063 depends on MEMCG && BLK_CGROUP
1066 menuconfig CGROUP_SCHED
1067 bool "CPU controller"
1070 This feature lets CPU scheduler recognize task groups and control CPU
1071 bandwidth allocation to such task groups. It uses cgroups to group
1075 config FAIR_GROUP_SCHED
1076 bool "Group scheduling for SCHED_OTHER"
1077 depends on CGROUP_SCHED
1078 default CGROUP_SCHED
1080 config CFS_BANDWIDTH
1081 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1082 depends on FAIR_GROUP_SCHED
1085 This option allows users to define CPU bandwidth rates (limits) for
1086 tasks running within the fair group scheduler. Groups with no limit
1087 set are considered to be unconstrained and will run with no
1089 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1091 config RT_GROUP_SCHED
1092 bool "Group scheduling for SCHED_RR/FIFO"
1093 depends on CGROUP_SCHED
1096 This feature lets you explicitly allocate real CPU bandwidth
1097 to task groups. If enabled, it will also make it impossible to
1098 schedule realtime tasks for non-root users until you allocate
1099 realtime bandwidth for them.
1100 See Documentation/scheduler/sched-rt-group.txt for more information.
1105 bool "PIDs controller"
1107 Provides enforcement of process number limits in the scope of a
1108 cgroup. Any attempt to fork more processes than is allowed in the
1109 cgroup will fail. PIDs are fundamentally a global resource because it
1110 is fairly trivial to reach PID exhaustion before you reach even a
1111 conservative kmemcg limit. As a result, it is possible to grind a
1112 system to halt without being limited by other cgroup policies. The
1113 PIDs controller is designed to stop this from happening.
1115 It should be noted that organisational operations (such as attaching
1116 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1117 since the PIDs limit only affects a process's ability to fork, not to
1121 bool "RDMA controller"
1123 Provides enforcement of RDMA resources defined by IB stack.
1124 It is fairly easy for consumers to exhaust RDMA resources, which
1125 can result into resource unavailability to other consumers.
1126 RDMA controller is designed to stop this from happening.
1127 Attaching processes with active RDMA resources to the cgroup
1128 hierarchy is allowed even if can cross the hierarchy's limit.
1130 config CGROUP_FREEZER
1131 bool "Freezer controller"
1133 Provides a way to freeze and unfreeze all tasks in a
1136 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1137 controller includes important in-kernel memory consumers per default.
1139 If you're using cgroup2, say N.
1141 config CGROUP_HUGETLB
1142 bool "HugeTLB controller"
1143 depends on HUGETLB_PAGE
1147 Provides a cgroup controller for HugeTLB pages.
1148 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1149 The limit is enforced during page fault. Since HugeTLB doesn't
1150 support page reclaim, enforcing the limit at page fault time implies
1151 that, the application will get SIGBUS signal if it tries to access
1152 HugeTLB pages beyond its limit. This requires the application to know
1153 beforehand how much HugeTLB pages it would require for its use. The
1154 control group is tracked in the third page lru pointer. This means
1155 that we cannot use the controller with huge page less than 3 pages.
1158 bool "Cpuset controller"
1160 This option will let you create and manage CPUSETs which
1161 allow dynamically partitioning a system into sets of CPUs and
1162 Memory Nodes and assigning tasks to run only within those sets.
1163 This is primarily useful on large SMP or NUMA systems.
1167 config PROC_PID_CPUSET
1168 bool "Include legacy /proc/<pid>/cpuset file"
1172 config CGROUP_DEVICE
1173 bool "Device controller"
1175 Provides a cgroup controller implementing whitelists for
1176 devices which a process in the cgroup can mknod or open.
1178 config CGROUP_CPUACCT
1179 bool "Simple CPU accounting controller"
1181 Provides a simple controller for monitoring the
1182 total CPU consumed by the tasks in a cgroup.
1185 bool "Perf controller"
1186 depends on PERF_EVENTS
1188 This option extends the perf per-cpu mode to restrict monitoring
1189 to threads which belong to the cgroup specified and run on the
1195 bool "Support for eBPF programs attached to cgroups"
1196 depends on BPF_SYSCALL
1197 select SOCK_CGROUP_DATA
1199 Allow attaching eBPF programs to a cgroup using the bpf(2)
1200 syscall command BPF_PROG_ATTACH.
1202 In which context these programs are accessed depends on the type
1203 of attachment. For instance, programs that are attached using
1204 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1208 bool "Example controller"
1211 This option enables a simple controller that exports
1212 debugging information about the cgroups framework.
1216 config SOCK_CGROUP_DATA
1222 config CHECKPOINT_RESTORE
1223 bool "Checkpoint/restore support" if EXPERT
1224 select PROC_CHILDREN
1227 Enables additional kernel features in a sake of checkpoint/restore.
1228 In particular it adds auxiliary prctl codes to setup process text,
1229 data and heap segment sizes, and a few additional /proc filesystem
1232 If unsure, say N here.
1234 menuconfig NAMESPACES
1235 bool "Namespaces support" if EXPERT
1236 depends on MULTIUSER
1239 Provides the way to make tasks work with different objects using
1240 the same id. For example same IPC id may refer to different objects
1241 or same user id or pid may refer to different tasks when used in
1242 different namespaces.
1247 bool "UTS namespace"
1250 In this namespace tasks see different info provided with the
1254 bool "IPC namespace"
1255 depends on (SYSVIPC || POSIX_MQUEUE)
1258 In this namespace tasks work with IPC ids which correspond to
1259 different IPC objects in different namespaces.
1262 bool "User namespace"
1265 This allows containers, i.e. vservers, to use user namespaces
1266 to provide different user info for different servers.
1268 When user namespaces are enabled in the kernel it is
1269 recommended that the MEMCG option also be enabled and that
1270 user-space use the memory control groups to limit the amount
1271 of memory a memory unprivileged users can use.
1276 bool "PID Namespaces"
1279 Support process id namespaces. This allows having multiple
1280 processes with the same pid as long as they are in different
1281 pid namespaces. This is a building block of containers.
1284 bool "Network namespace"
1288 Allow user space to create what appear to be multiple instances
1289 of the network stack.
1293 config SCHED_AUTOGROUP
1294 bool "Automatic process group scheduling"
1297 select FAIR_GROUP_SCHED
1299 This option optimizes the scheduler for common desktop workloads by
1300 automatically creating and populating task groups. This separation
1301 of workloads isolates aggressive CPU burners (like build jobs) from
1302 desktop applications. Task group autogeneration is currently based
1305 config SYSFS_DEPRECATED
1306 bool "Enable deprecated sysfs features to support old userspace tools"
1310 This option adds code that switches the layout of the "block" class
1311 devices, to not show up in /sys/class/block/, but only in
1314 This switch is only active when the sysfs.deprecated=1 boot option is
1315 passed or the SYSFS_DEPRECATED_V2 option is set.
1317 This option allows new kernels to run on old distributions and tools,
1318 which might get confused by /sys/class/block/. Since 2007/2008 all
1319 major distributions and tools handle this just fine.
1321 Recent distributions and userspace tools after 2009/2010 depend on
1322 the existence of /sys/class/block/, and will not work with this
1325 Only if you are using a new kernel on an old distribution, you might
1328 config SYSFS_DEPRECATED_V2
1329 bool "Enable deprecated sysfs features by default"
1332 depends on SYSFS_DEPRECATED
1334 Enable deprecated sysfs by default.
1336 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1339 Only if you are using a new kernel on an old distribution, you might
1340 need to say Y here. Even then, odds are you would not need it
1341 enabled, you can always pass the boot option if absolutely necessary.
1344 bool "Kernel->user space relay support (formerly relayfs)"
1347 This option enables support for relay interface support in
1348 certain file systems (such as debugfs).
1349 It is designed to provide an efficient mechanism for tools and
1350 facilities to relay large amounts of data from kernel space to
1355 config BLK_DEV_INITRD
1356 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1357 depends on BROKEN || !FRV
1359 The initial RAM filesystem is a ramfs which is loaded by the
1360 boot loader (loadlin or lilo) and that is mounted as root
1361 before the normal boot procedure. It is typically used to
1362 load modules needed to mount the "real" root file system,
1363 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1365 If RAM disk support (BLK_DEV_RAM) is also included, this
1366 also enables initial RAM disk (initrd) support and adds
1367 15 Kbytes (more on some other architectures) to the kernel size.
1373 source "usr/Kconfig"
1378 prompt "Compiler optimization level"
1379 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1381 config CC_OPTIMIZE_FOR_PERFORMANCE
1382 bool "Optimize for performance"
1384 This is the default optimization level for the kernel, building
1385 with the "-O2" compiler flag for best performance and most
1386 helpful compile-time warnings.
1388 config CC_OPTIMIZE_FOR_SIZE
1389 bool "Optimize for size"
1391 Enabling this option will pass "-Os" instead of "-O2" to
1392 your compiler resulting in a smaller kernel.
1407 config SYSCTL_EXCEPTION_TRACE
1410 Enable support for /proc/sys/debug/exception-trace.
1412 config SYSCTL_ARCH_UNALIGN_NO_WARN
1415 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1416 Allows arch to define/use @no_unaligned_warning to possibly warn
1417 about unaligned access emulation going on under the hood.
1419 config SYSCTL_ARCH_UNALIGN_ALLOW
1422 Enable support for /proc/sys/kernel/unaligned-trap
1423 Allows arches to define/use @unaligned_enabled to runtime toggle
1424 the unaligned access emulation.
1425 see arch/parisc/kernel/unaligned.c for reference
1427 config HAVE_PCSPKR_PLATFORM
1430 # interpreter that classic socket filters depend on
1435 bool "Configure standard kernel features (expert users)"
1436 # Unhide debug options, to make the on-by-default options visible
1439 This option allows certain base kernel options and settings
1440 to be disabled or tweaked. This is for specialized
1441 environments which can tolerate a "non-standard" kernel.
1442 Only use this if you really know what you are doing.
1445 bool "Enable 16-bit UID system calls" if EXPERT
1446 depends on HAVE_UID16 && MULTIUSER
1449 This enables the legacy 16-bit UID syscall wrappers.
1452 bool "Multiple users, groups and capabilities support" if EXPERT
1455 This option enables support for non-root users, groups and
1458 If you say N here, all processes will run with UID 0, GID 0, and all
1459 possible capabilities. Saying N here also compiles out support for
1460 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1463 If unsure, say Y here.
1465 config SGETMASK_SYSCALL
1466 bool "sgetmask/ssetmask syscalls support" if EXPERT
1467 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1469 sys_sgetmask and sys_ssetmask are obsolete system calls
1470 no longer supported in libc but still enabled by default in some
1473 If unsure, leave the default option here.
1475 config SYSFS_SYSCALL
1476 bool "Sysfs syscall support" if EXPERT
1479 sys_sysfs is an obsolete system call no longer supported in libc.
1480 Note that disabling this option is more secure but might break
1481 compatibility with some systems.
1483 If unsure say Y here.
1485 config SYSCTL_SYSCALL
1486 bool "Sysctl syscall support" if EXPERT
1487 depends on PROC_SYSCTL
1491 sys_sysctl uses binary paths that have been found challenging
1492 to properly maintain and use. The interface in /proc/sys
1493 using paths with ascii names is now the primary path to this
1496 Almost nothing using the binary sysctl interface so if you are
1497 trying to save some space it is probably safe to disable this,
1498 making your kernel marginally smaller.
1500 If unsure say N here.
1503 bool "Posix Clocks & timers" if EXPERT
1506 This includes native support for POSIX timers to the kernel.
1507 Some embedded systems have no use for them and therefore they
1508 can be configured out to reduce the size of the kernel image.
1510 When this option is disabled, the following syscalls won't be
1511 available: timer_create, timer_gettime: timer_getoverrun,
1512 timer_settime, timer_delete, clock_adjtime, getitimer,
1513 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1514 clock_getres and clock_nanosleep syscalls will be limited to
1515 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1520 bool "Load all symbols for debugging/ksymoops" if EXPERT
1523 Say Y here to let the kernel print out symbolic crash information and
1524 symbolic stack backtraces. This increases the size of the kernel
1525 somewhat, as all symbols have to be loaded into the kernel image.
1528 bool "Include all symbols in kallsyms"
1529 depends on DEBUG_KERNEL && KALLSYMS
1531 Normally kallsyms only contains the symbols of functions for nicer
1532 OOPS messages and backtraces (i.e., symbols from the text and inittext
1533 sections). This is sufficient for most cases. And only in very rare
1534 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1535 names of variables from the data sections, etc).
1537 This option makes sure that all symbols are loaded into the kernel
1538 image (i.e., symbols from all sections) in cost of increased kernel
1539 size (depending on the kernel configuration, it may be 300KiB or
1540 something like this).
1542 Say N unless you really need all symbols.
1544 config KALLSYMS_ABSOLUTE_PERCPU
1547 default X86_64 && SMP
1549 config KALLSYMS_BASE_RELATIVE
1552 default !IA64 && !(TILE && 64BIT)
1554 Instead of emitting them as absolute values in the native word size,
1555 emit the symbol references in the kallsyms table as 32-bit entries,
1556 each containing a relative value in the range [base, base + U32_MAX]
1557 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1558 an absolute value in the range [0, S32_MAX] or a relative value in the
1559 range [base, base + S32_MAX], where base is the lowest relative symbol
1560 address encountered in the image.
1562 On 64-bit builds, this reduces the size of the address table by 50%,
1563 but more importantly, it results in entries whose values are build
1564 time constants, and no relocation pass is required at runtime to fix
1565 up the entries based on the runtime load address of the kernel.
1569 bool "Enable support for printk" if EXPERT
1572 This option enables normal printk support. Removing it
1573 eliminates most of the message strings from the kernel image
1574 and makes the kernel more or less silent. As this makes it
1575 very difficult to diagnose system problems, saying N here is
1576 strongly discouraged.
1584 bool "BUG() support" if EXPERT
1587 Disabling this option eliminates support for BUG and WARN, reducing
1588 the size of your kernel image and potentially quietly ignoring
1589 numerous fatal conditions. You should only consider disabling this
1590 option for embedded systems with no facilities for reporting errors.
1596 bool "Enable ELF core dumps" if EXPERT
1598 Enable support for generating core dumps. Disabling saves about 4k.
1601 config PCSPKR_PLATFORM
1602 bool "Enable PC-Speaker support" if EXPERT
1603 depends on HAVE_PCSPKR_PLATFORM
1607 This option allows to disable the internal PC-Speaker
1608 support, saving some memory.
1612 bool "Enable full-sized data structures for core" if EXPERT
1614 Disabling this option reduces the size of miscellaneous core
1615 kernel data structures. This saves memory on small machines,
1616 but may reduce performance.
1619 bool "Enable futex support" if EXPERT
1623 Disabling this option will cause the kernel to be built without
1624 support for "fast userspace mutexes". The resulting kernel may not
1625 run glibc-based applications correctly.
1627 config HAVE_FUTEX_CMPXCHG
1631 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1632 is implemented and always working. This removes a couple of runtime
1636 bool "Enable eventpoll support" if EXPERT
1640 Disabling this option will cause the kernel to be built without
1641 support for epoll family of system calls.
1644 bool "Enable signalfd() system call" if EXPERT
1648 Enable the signalfd() system call that allows to receive signals
1649 on a file descriptor.
1654 bool "Enable timerfd() system call" if EXPERT
1658 Enable the timerfd() system call that allows to receive timer
1659 events on a file descriptor.
1664 bool "Enable eventfd() system call" if EXPERT
1668 Enable the eventfd() system call that allows to receive both
1669 kernel notification (ie. KAIO) or userspace notifications.
1673 # syscall, maps, verifier
1675 bool "Enable bpf() system call"
1680 Enable the bpf() system call that allows to manipulate eBPF
1681 programs and maps via file descriptors.
1684 bool "Use full shmem filesystem" if EXPERT
1688 The shmem is an internal filesystem used to manage shared memory.
1689 It is backed by swap and manages resource limits. It is also exported
1690 to userspace as tmpfs if TMPFS is enabled. Disabling this
1691 option replaces shmem and tmpfs with the much simpler ramfs code,
1692 which may be appropriate on small systems without swap.
1695 bool "Enable AIO support" if EXPERT
1698 This option enables POSIX asynchronous I/O which may by used
1699 by some high performance threaded applications. Disabling
1700 this option saves about 7k.
1702 config ADVISE_SYSCALLS
1703 bool "Enable madvise/fadvise syscalls" if EXPERT
1706 This option enables the madvise and fadvise syscalls, used by
1707 applications to advise the kernel about their future memory or file
1708 usage, improving performance. If building an embedded system where no
1709 applications use these syscalls, you can disable this option to save
1713 bool "Enable userfaultfd() system call"
1717 Enable the userfaultfd() system call that allows to intercept and
1718 handle page faults in userland.
1722 bool "Enable PCI quirk workarounds" if EXPERT
1725 This enables workarounds for various PCI chipset
1726 bugs/quirks. Disable this only if your target machine is
1727 unaffected by PCI quirks.
1730 bool "Enable membarrier() system call" if EXPERT
1733 Enable the membarrier() system call that allows issuing memory
1734 barriers across all running threads, which can be used to distribute
1735 the cost of user-space memory barriers asymmetrically by transforming
1736 pairs of memory barriers into pairs consisting of membarrier() and a
1742 bool "Embedded system"
1743 option allnoconfig_y
1746 This option should be enabled if compiling the kernel for
1747 an embedded system so certain expert options are available
1750 config HAVE_PERF_EVENTS
1753 See tools/perf/design.txt for details.
1755 config PERF_USE_VMALLOC
1758 See tools/perf/design.txt for details
1761 bool "PC/104 support"
1763 Expose PC/104 form factor device drivers and options available for
1764 selection and configuration. Enable this option if your target
1765 machine has a PC/104 bus.
1767 menu "Kernel Performance Events And Counters"
1770 bool "Kernel performance events and counters"
1771 default y if PROFILING
1772 depends on HAVE_PERF_EVENTS
1777 Enable kernel support for various performance events provided
1778 by software and hardware.
1780 Software events are supported either built-in or via the
1781 use of generic tracepoints.
1783 Most modern CPUs support performance events via performance
1784 counter registers. These registers count the number of certain
1785 types of hw events: such as instructions executed, cachemisses
1786 suffered, or branches mis-predicted - without slowing down the
1787 kernel or applications. These registers can also trigger interrupts
1788 when a threshold number of events have passed - and can thus be
1789 used to profile the code that runs on that CPU.
1791 The Linux Performance Event subsystem provides an abstraction of
1792 these software and hardware event capabilities, available via a
1793 system call and used by the "perf" utility in tools/perf/. It
1794 provides per task and per CPU counters, and it provides event
1795 capabilities on top of those.
1799 config DEBUG_PERF_USE_VMALLOC
1801 bool "Debug: use vmalloc to back perf mmap() buffers"
1802 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1803 select PERF_USE_VMALLOC
1805 Use vmalloc memory to back perf mmap() buffers.
1807 Mostly useful for debugging the vmalloc code on platforms
1808 that don't require it.
1814 config VM_EVENT_COUNTERS
1816 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1818 VM event counters are needed for event counts to be shown.
1819 This option allows the disabling of the VM event counters
1820 on EXPERT systems. /proc/vmstat will only show page counts
1821 if VM event counters are disabled.
1825 bool "Enable SLUB debugging support" if EXPERT
1826 depends on SLUB && SYSFS
1828 SLUB has extensive debug support features. Disabling these can
1829 result in significant savings in code size. This also disables
1830 SLUB sysfs support. /sys/slab will not exist and there will be
1831 no support for cache validation etc.
1833 config SLUB_MEMCG_SYSFS_ON
1835 bool "Enable memcg SLUB sysfs support by default" if EXPERT
1836 depends on SLUB && SYSFS && MEMCG
1838 SLUB creates a directory under /sys/kernel/slab for each
1839 allocation cache to host info and debug files. If memory
1840 cgroup is enabled, each cache can have per memory cgroup
1841 caches. SLUB can create the same sysfs directories for these
1842 caches under /sys/kernel/slab/CACHE/cgroup but it can lead
1843 to a very high number of debug files being created. This is
1844 controlled by slub_memcg_sysfs boot parameter and this
1845 config option determines the parameter's default value.
1848 bool "Disable heap randomization"
1851 Randomizing heap placement makes heap exploits harder, but it
1852 also breaks ancient binaries (including anything libc5 based).
1853 This option changes the bootup default to heap randomization
1854 disabled, and can be overridden at runtime by setting
1855 /proc/sys/kernel/randomize_va_space to 2.
1857 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1860 prompt "Choose SLAB allocator"
1863 This option allows to select a slab allocator.
1867 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1869 The regular slab allocator that is established and known to work
1870 well in all environments. It organizes cache hot objects in
1871 per cpu and per node queues.
1874 bool "SLUB (Unqueued Allocator)"
1875 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1877 SLUB is a slab allocator that minimizes cache line usage
1878 instead of managing queues of cached objects (SLAB approach).
1879 Per cpu caching is realized using slabs of objects instead
1880 of queues of objects. SLUB can use memory efficiently
1881 and has enhanced diagnostics. SLUB is the default choice for
1886 bool "SLOB (Simple Allocator)"
1888 SLOB replaces the stock allocator with a drastically simpler
1889 allocator. SLOB is generally more space efficient but
1890 does not perform as well on large systems.
1894 config SLAB_FREELIST_RANDOM
1896 depends on SLAB || SLUB
1897 bool "SLAB freelist randomization"
1899 Randomizes the freelist order used on creating new pages. This
1900 security feature reduces the predictability of the kernel slab
1901 allocator against heap overflows.
1903 config SLUB_CPU_PARTIAL
1905 depends on SLUB && SMP
1906 bool "SLUB per cpu partial cache"
1908 Per cpu partial caches accellerate objects allocation and freeing
1909 that is local to a processor at the price of more indeterminism
1910 in the latency of the free. On overflow these caches will be cleared
1911 which requires the taking of locks that may cause latency spikes.
1912 Typically one would choose no for a realtime system.
1914 config MMAP_ALLOW_UNINITIALIZED
1915 bool "Allow mmapped anonymous memory to be uninitialized"
1916 depends on EXPERT && !MMU
1919 Normally, and according to the Linux spec, anonymous memory obtained
1920 from mmap() has it's contents cleared before it is passed to
1921 userspace. Enabling this config option allows you to request that
1922 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1923 providing a huge performance boost. If this option is not enabled,
1924 then the flag will be ignored.
1926 This is taken advantage of by uClibc's malloc(), and also by
1927 ELF-FDPIC binfmt's brk and stack allocator.
1929 Because of the obvious security issues, this option should only be
1930 enabled on embedded devices where you control what is run in
1931 userspace. Since that isn't generally a problem on no-MMU systems,
1932 it is normally safe to say Y here.
1934 See Documentation/nommu-mmap.txt for more information.
1936 config SYSTEM_DATA_VERIFICATION
1938 select SYSTEM_TRUSTED_KEYRING
1942 select ASYMMETRIC_KEY_TYPE
1943 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1946 select X509_CERTIFICATE_PARSER
1947 select PKCS7_MESSAGE_PARSER
1949 Provide PKCS#7 message verification using the contents of the system
1950 trusted keyring to provide public keys. This then can be used for
1951 module verification, kexec image verification and firmware blob
1955 bool "Profiling support"
1957 Say Y here to enable the extended profiling support mechanisms used
1958 by profilers such as OProfile.
1961 # Place an empty function call at each tracepoint site. Can be
1962 # dynamically changed for a probe function.
1967 source "arch/Kconfig"
1969 endmenu # General setup
1971 config HAVE_GENERIC_DMA_COHERENT
1978 depends on SLAB || SLUB_DEBUG
1986 default 0 if BASE_FULL
1987 default 1 if !BASE_FULL
1990 bool "Enable loadable module support"
1993 Kernel modules are small pieces of compiled code which can
1994 be inserted in the running kernel, rather than being
1995 permanently built into the kernel. You use the "modprobe"
1996 tool to add (and sometimes remove) them. If you say Y here,
1997 many parts of the kernel can be built as modules (by
1998 answering M instead of Y where indicated): this is most
1999 useful for infrequently used options which are not required
2000 for booting. For more information, see the man pages for
2001 modprobe, lsmod, modinfo, insmod and rmmod.
2003 If you say Y here, you will need to run "make
2004 modules_install" to put the modules under /lib/modules/
2005 where modprobe can find them (you may need to be root to do
2012 config MODULE_FORCE_LOAD
2013 bool "Forced module loading"
2016 Allow loading of modules without version information (ie. modprobe
2017 --force). Forced module loading sets the 'F' (forced) taint flag and
2018 is usually a really bad idea.
2020 config MODULE_UNLOAD
2021 bool "Module unloading"
2023 Without this option you will not be able to unload any
2024 modules (note that some modules may not be unloadable
2025 anyway), which makes your kernel smaller, faster
2026 and simpler. If unsure, say Y.
2028 config MODULE_FORCE_UNLOAD
2029 bool "Forced module unloading"
2030 depends on MODULE_UNLOAD
2032 This option allows you to force a module to unload, even if the
2033 kernel believes it is unsafe: the kernel will remove the module
2034 without waiting for anyone to stop using it (using the -f option to
2035 rmmod). This is mainly for kernel developers and desperate users.
2039 bool "Module versioning support"
2041 Usually, you have to use modules compiled with your kernel.
2042 Saying Y here makes it sometimes possible to use modules
2043 compiled for different kernels, by adding enough information
2044 to the modules to (hopefully) spot any changes which would
2045 make them incompatible with the kernel you are running. If
2048 config MODULE_REL_CRCS
2050 depends on MODVERSIONS
2052 config MODULE_SRCVERSION_ALL
2053 bool "Source checksum for all modules"
2055 Modules which contain a MODULE_VERSION get an extra "srcversion"
2056 field inserted into their modinfo section, which contains a
2057 sum of the source files which made it. This helps maintainers
2058 see exactly which source was used to build a module (since
2059 others sometimes change the module source without updating
2060 the version). With this option, such a "srcversion" field
2061 will be created for all modules. If unsure, say N.
2064 bool "Module signature verification"
2066 select SYSTEM_DATA_VERIFICATION
2068 Check modules for valid signatures upon load: the signature
2069 is simply appended to the module. For more information see
2070 Documentation/module-signing.txt.
2072 Note that this option adds the OpenSSL development packages as a
2073 kernel build dependency so that the signing tool can use its crypto
2076 !!!WARNING!!! If you enable this option, you MUST make sure that the
2077 module DOES NOT get stripped after being signed. This includes the
2078 debuginfo strip done by some packagers (such as rpmbuild) and
2079 inclusion into an initramfs that wants the module size reduced.
2081 config MODULE_SIG_FORCE
2082 bool "Require modules to be validly signed"
2083 depends on MODULE_SIG
2085 Reject unsigned modules or signed modules for which we don't have a
2086 key. Without this, such modules will simply taint the kernel.
2088 config MODULE_SIG_ALL
2089 bool "Automatically sign all modules"
2091 depends on MODULE_SIG
2093 Sign all modules during make modules_install. Without this option,
2094 modules must be signed manually, using the scripts/sign-file tool.
2096 comment "Do not forget to sign required modules with scripts/sign-file"
2097 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2100 prompt "Which hash algorithm should modules be signed with?"
2101 depends on MODULE_SIG
2103 This determines which sort of hashing algorithm will be used during
2104 signature generation. This algorithm _must_ be built into the kernel
2105 directly so that signature verification can take place. It is not
2106 possible to load a signed module containing the algorithm to check
2107 the signature on that module.
2109 config MODULE_SIG_SHA1
2110 bool "Sign modules with SHA-1"
2113 config MODULE_SIG_SHA224
2114 bool "Sign modules with SHA-224"
2115 select CRYPTO_SHA256
2117 config MODULE_SIG_SHA256
2118 bool "Sign modules with SHA-256"
2119 select CRYPTO_SHA256
2121 config MODULE_SIG_SHA384
2122 bool "Sign modules with SHA-384"
2123 select CRYPTO_SHA512
2125 config MODULE_SIG_SHA512
2126 bool "Sign modules with SHA-512"
2127 select CRYPTO_SHA512
2131 config MODULE_SIG_HASH
2133 depends on MODULE_SIG
2134 default "sha1" if MODULE_SIG_SHA1
2135 default "sha224" if MODULE_SIG_SHA224
2136 default "sha256" if MODULE_SIG_SHA256
2137 default "sha384" if MODULE_SIG_SHA384
2138 default "sha512" if MODULE_SIG_SHA512
2140 config MODULE_COMPRESS
2141 bool "Compress modules on installation"
2145 Compresses kernel modules when 'make modules_install' is run; gzip or
2146 xz depending on "Compression algorithm" below.
2148 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2150 Out-of-tree kernel modules installed using Kbuild will also be
2151 compressed upon installation.
2153 Note: for modules inside an initrd or initramfs, it's more efficient
2154 to compress the whole initrd or initramfs instead.
2156 Note: This is fully compatible with signed modules.
2161 prompt "Compression algorithm"
2162 depends on MODULE_COMPRESS
2163 default MODULE_COMPRESS_GZIP
2165 This determines which sort of compression will be used during
2166 'make modules_install'.
2168 GZIP (default) and XZ are supported.
2170 config MODULE_COMPRESS_GZIP
2173 config MODULE_COMPRESS_XZ
2178 config TRIM_UNUSED_KSYMS
2179 bool "Trim unused exported kernel symbols"
2180 depends on MODULES && !UNUSED_SYMBOLS
2182 The kernel and some modules make many symbols available for
2183 other modules to use via EXPORT_SYMBOL() and variants. Depending
2184 on the set of modules being selected in your kernel configuration,
2185 many of those exported symbols might never be used.
2187 This option allows for unused exported symbols to be dropped from
2188 the build. In turn, this provides the compiler more opportunities
2189 (especially when using LTO) for optimizing the code and reducing
2190 binary size. This might have some security advantages as well.
2192 If unsure, or if you need to build out-of-tree modules, say N.
2196 config MODULES_TREE_LOOKUP
2198 depends on PERF_EVENTS || TRACING
2200 config INIT_ALL_POSSIBLE
2203 Back when each arch used to define their own cpu_online_mask and
2204 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2205 with all 1s, and others with all 0s. When they were centralised,
2206 it was better to provide this option than to break all the archs
2207 and have several arch maintainers pursuing me down dark alleys.
2209 source "block/Kconfig"
2211 config PREEMPT_NOTIFIERS
2221 Build a simple ASN.1 grammar compiler that produces a bytecode output
2222 that can be interpreted by the ASN.1 stream decoder and used to
2223 inform it as to what tags are to be expected in a stream and what
2224 functions to call on what tags.
2226 source "kernel/Kconfig.locks"
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