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.
525 This option selects the sleepable version of RCU. This version
526 permits arbitrary sleeping or blocking within RCU read-side critical
534 This option enables a task-based RCU implementation that uses
535 only voluntary context switch (not preemption!), idle, and
536 user-mode execution as quiescent states.
538 config RCU_STALL_COMMON
539 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
541 This option enables RCU CPU stall code that is common between
542 the TINY and TREE variants of RCU. The purpose is to allow
543 the tiny variants to disable RCU CPU stall warnings, while
544 making these warnings mandatory for the tree variants.
546 config CONTEXT_TRACKING
549 config CONTEXT_TRACKING_FORCE
550 bool "Force context tracking"
551 depends on CONTEXT_TRACKING
552 default y if !NO_HZ_FULL
554 The major pre-requirement for full dynticks to work is to
555 support the context tracking subsystem. But there are also
556 other dependencies to provide in order to make the full
559 This option stands for testing when an arch implements the
560 context tracking backend but doesn't yet fullfill all the
561 requirements to make the full dynticks feature working.
562 Without the full dynticks, there is no way to test the support
563 for context tracking and the subsystems that rely on it: RCU
564 userspace extended quiescent state and tickless cputime
565 accounting. This option copes with the absence of the full
566 dynticks subsystem by forcing the context tracking on all
569 Say Y only if you're working on the development of an
570 architecture backend for the context tracking.
572 Say N otherwise, this option brings an overhead that you
573 don't want in production.
577 int "Tree-based hierarchical RCU fanout value"
580 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
584 This option controls the fanout of hierarchical implementations
585 of RCU, allowing RCU to work efficiently on machines with
586 large numbers of CPUs. This value must be at least the fourth
587 root of NR_CPUS, which allows NR_CPUS to be insanely large.
588 The default value of RCU_FANOUT should be used for production
589 systems, but if you are stress-testing the RCU implementation
590 itself, small RCU_FANOUT values allow you to test large-system
591 code paths on small(er) systems.
593 Select a specific number if testing RCU itself.
594 Take the default if unsure.
596 config RCU_FANOUT_LEAF
597 int "Tree-based hierarchical RCU leaf-level fanout value"
600 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
603 This option controls the leaf-level fanout of hierarchical
604 implementations of RCU, and allows trading off cache misses
605 against lock contention. Systems that synchronize their
606 scheduling-clock interrupts for energy-efficiency reasons will
607 want the default because the smaller leaf-level fanout keeps
608 lock contention levels acceptably low. Very large systems
609 (hundreds or thousands of CPUs) will instead want to set this
610 value to the maximum value possible in order to reduce the
611 number of cache misses incurred during RCU's grace-period
612 initialization. These systems tend to run CPU-bound, and thus
613 are not helped by synchronized interrupts, and thus tend to
614 skew them, which reduces lock contention enough that large
615 leaf-level fanouts work well.
617 Select a specific number if testing RCU itself.
619 Select the maximum permissible value for large systems.
621 Take the default if unsure.
623 config RCU_FAST_NO_HZ
624 bool "Accelerate last non-dyntick-idle CPU's grace periods"
625 depends on NO_HZ_COMMON && SMP && RCU_EXPERT
628 This option permits CPUs to enter dynticks-idle state even if
629 they have RCU callbacks queued, and prevents RCU from waking
630 these CPUs up more than roughly once every four jiffies (by
631 default, you can adjust this using the rcutree.rcu_idle_gp_delay
632 parameter), thus improving energy efficiency. On the other
633 hand, this option increases the duration of RCU grace periods,
634 for example, slowing down synchronize_rcu().
636 Say Y if energy efficiency is critically important, and you
637 don't care about increased grace-period durations.
639 Say N if you are unsure.
641 config TREE_RCU_TRACE
642 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
645 This option provides tracing for the TREE_RCU and
646 PREEMPT_RCU implementations, permitting Makefile to
647 trivially select kernel/rcutree_trace.c.
650 bool "Enable RCU priority boosting"
651 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
654 This option boosts the priority of preempted RCU readers that
655 block the current preemptible RCU grace period for too long.
656 This option also prevents heavy loads from blocking RCU
657 callback invocation for all flavors of RCU.
659 Say Y here if you are working with real-time apps or heavy loads
660 Say N here if you are unsure.
662 config RCU_KTHREAD_PRIO
663 int "Real-time priority to use for RCU worker threads"
664 range 1 99 if RCU_BOOST
665 range 0 99 if !RCU_BOOST
666 default 1 if RCU_BOOST
667 default 0 if !RCU_BOOST
668 depends on RCU_EXPERT
670 This option specifies the SCHED_FIFO priority value that will be
671 assigned to the rcuc/n and rcub/n threads and is also the value
672 used for RCU_BOOST (if enabled). If you are working with a
673 real-time application that has one or more CPU-bound threads
674 running at a real-time priority level, you should set
675 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
676 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
677 value of 1 is appropriate in the common case, which is real-time
678 applications that do not have any CPU-bound threads.
680 Some real-time applications might not have a single real-time
681 thread that saturates a given CPU, but instead might have
682 multiple real-time threads that, taken together, fully utilize
683 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
684 a priority higher than the lowest-priority thread that is
685 conspiring to prevent the CPU from running any non-real-time
686 tasks. For example, if one thread at priority 10 and another
687 thread at priority 5 are between themselves fully consuming
688 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
689 set to priority 6 or higher.
691 Specify the real-time priority, or take the default if unsure.
693 config RCU_BOOST_DELAY
694 int "Milliseconds to delay boosting after RCU grace-period start"
699 This option specifies the time to wait after the beginning of
700 a given grace period before priority-boosting preempted RCU
701 readers blocking that grace period. Note that any RCU reader
702 blocking an expedited RCU grace period is boosted immediately.
704 Accept the default if unsure.
707 bool "Offload RCU callback processing from boot-selected CPUs"
708 depends on TREE_RCU || PREEMPT_RCU
709 depends on RCU_EXPERT || NO_HZ_FULL
712 Use this option to reduce OS jitter for aggressive HPC or
713 real-time workloads. It can also be used to offload RCU
714 callback invocation to energy-efficient CPUs in battery-powered
715 asymmetric multiprocessors.
717 This option offloads callback invocation from the set of
718 CPUs specified at boot time by the rcu_nocbs parameter.
719 For each such CPU, a kthread ("rcuox/N") will be created to
720 invoke callbacks, where the "N" is the CPU being offloaded,
721 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
722 "s" for RCU-sched. Nothing prevents this kthread from running
723 on the specified CPUs, but (1) the kthreads may be preempted
724 between each callback, and (2) affinity or cgroups can be used
725 to force the kthreads to run on whatever set of CPUs is desired.
727 Say Y here if you want to help to debug reduced OS jitter.
728 Say N here if you are unsure.
731 prompt "Build-forced no-CBs CPUs"
732 default RCU_NOCB_CPU_NONE
733 depends on RCU_NOCB_CPU
735 This option allows no-CBs CPUs (whose RCU callbacks are invoked
736 from kthreads rather than from softirq context) to be specified
737 at build time. Additional no-CBs CPUs may be specified by
738 the rcu_nocbs= boot parameter.
740 config RCU_NOCB_CPU_NONE
741 bool "No build_forced no-CBs CPUs"
743 This option does not force any of the CPUs to be no-CBs CPUs.
744 Only CPUs designated by the rcu_nocbs= boot parameter will be
745 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
746 kthreads whose names begin with "rcuo". All other CPUs will
747 invoke their own RCU callbacks in softirq context.
749 Select this option if you want to choose no-CBs CPUs at
750 boot time, for example, to allow testing of different no-CBs
751 configurations without having to rebuild the kernel each time.
753 config RCU_NOCB_CPU_ZERO
754 bool "CPU 0 is a build_forced no-CBs CPU"
756 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
757 callbacks are invoked by a per-CPU kthread whose name begins
758 with "rcuo". Additional CPUs may be designated as no-CBs
759 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
760 All other CPUs will invoke their own RCU callbacks in softirq
763 Select this if CPU 0 needs to be a no-CBs CPU for real-time
764 or energy-efficiency reasons, but the real reason it exists
765 is to ensure that randconfig testing covers mixed systems.
767 config RCU_NOCB_CPU_ALL
768 bool "All CPUs are build_forced no-CBs CPUs"
770 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
771 boot parameter will be ignored. All CPUs' RCU callbacks will
772 be executed in the context of per-CPU rcuo kthreads created for
773 this purpose. Assuming that the kthreads whose names start with
774 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
775 on the remaining CPUs, but might decrease memory locality during
776 RCU-callback invocation, thus potentially degrading throughput.
778 Select this if all CPUs need to be no-CBs CPUs for real-time
779 or energy-efficiency reasons.
783 endmenu # "RCU Subsystem"
790 tristate "Kernel .config support"
793 This option enables the complete Linux kernel ".config" file
794 contents to be saved in the kernel. It provides documentation
795 of which kernel options are used in a running kernel or in an
796 on-disk kernel. This information can be extracted from the kernel
797 image file with the script scripts/extract-ikconfig and used as
798 input to rebuild the current kernel or to build another kernel.
799 It can also be extracted from a running kernel by reading
800 /proc/config.gz if enabled (below).
803 bool "Enable access to .config through /proc/config.gz"
804 depends on IKCONFIG && PROC_FS
806 This option enables access to the kernel configuration file
807 through /proc/config.gz.
810 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
815 Select the minimal kernel log buffer size as a power of 2.
816 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
817 parameter, see below. Any higher size also might be forced
818 by "log_buf_len" boot parameter.
828 config LOG_CPU_MAX_BUF_SHIFT
829 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
832 default 12 if !BASE_SMALL
833 default 0 if BASE_SMALL
836 This option allows to increase the default ring buffer size
837 according to the number of CPUs. The value defines the contribution
838 of each CPU as a power of 2. The used space is typically only few
839 lines however it might be much more when problems are reported,
842 The increased size means that a new buffer has to be allocated and
843 the original static one is unused. It makes sense only on systems
844 with more CPUs. Therefore this value is used only when the sum of
845 contributions is greater than the half of the default kernel ring
846 buffer as defined by LOG_BUF_SHIFT. The default values are set
847 so that more than 64 CPUs are needed to trigger the allocation.
849 Also this option is ignored when "log_buf_len" kernel parameter is
850 used as it forces an exact (power of two) size of the ring buffer.
852 The number of possible CPUs is used for this computation ignoring
853 hotplugging making the computation optimal for the worst case
854 scenario while allowing a simple algorithm to be used from bootup.
856 Examples shift values and their meaning:
857 17 => 128 KB for each CPU
858 16 => 64 KB for each CPU
859 15 => 32 KB for each CPU
860 14 => 16 KB for each CPU
861 13 => 8 KB for each CPU
862 12 => 4 KB for each CPU
864 config NMI_LOG_BUF_SHIFT
865 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
868 depends on PRINTK_NMI
870 Select the size of a per-CPU buffer where NMI messages are temporary
871 stored. They are copied to the main log buffer in a safe context
872 to avoid a deadlock. The value defines the size as a power of 2.
874 NMI messages are rare and limited. The largest one is when
875 a backtrace is printed. It usually fits into 4KB. Select
876 8KB if you want to be on the safe side.
879 17 => 128 KB for each CPU
880 16 => 64 KB for each CPU
881 15 => 32 KB for each CPU
882 14 => 16 KB for each CPU
883 13 => 8 KB for each CPU
884 12 => 4 KB for each CPU
887 # Architectures with an unreliable sched_clock() should select this:
889 config HAVE_UNSTABLE_SCHED_CLOCK
892 config GENERIC_SCHED_CLOCK
896 # For architectures that want to enable the support for NUMA-affine scheduler
899 config ARCH_SUPPORTS_NUMA_BALANCING
903 # For architectures that prefer to flush all TLBs after a number of pages
904 # are unmapped instead of sending one IPI per page to flush. The architecture
905 # must provide guarantees on what happens if a clean TLB cache entry is
906 # written after the unmap. Details are in mm/rmap.c near the check for
907 # should_defer_flush. The architecture should also consider if the full flush
908 # and the refill costs are offset by the savings of sending fewer IPIs.
909 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
913 # For architectures that know their GCC __int128 support is sound
915 config ARCH_SUPPORTS_INT128
918 # For architectures that (ab)use NUMA to represent different memory regions
919 # all cpu-local but of different latencies, such as SuperH.
921 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
924 config NUMA_BALANCING
925 bool "Memory placement aware NUMA scheduler"
926 depends on ARCH_SUPPORTS_NUMA_BALANCING
927 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
928 depends on SMP && NUMA && MIGRATION
930 This option adds support for automatic NUMA aware memory/task placement.
931 The mechanism is quite primitive and is based on migrating memory when
932 it has references to the node the task is running on.
934 This system will be inactive on UMA systems.
936 config NUMA_BALANCING_DEFAULT_ENABLED
937 bool "Automatically enable NUMA aware memory/task placement"
939 depends on NUMA_BALANCING
941 If set, automatic NUMA balancing will be enabled if running on a NUMA
945 bool "Control Group support"
948 This option adds support for grouping sets of processes together, for
949 use with process control subsystems such as Cpusets, CFS, memory
950 controls or device isolation.
952 - Documentation/scheduler/sched-design-CFS.txt (CFS)
953 - Documentation/cgroup-v1/ (features for grouping, isolation
954 and resource control)
964 bool "Memory controller"
968 Provides control over the memory footprint of tasks in a cgroup.
971 bool "Swap controller"
972 depends on MEMCG && SWAP
974 Provides control over the swap space consumed by tasks in a cgroup.
976 config MEMCG_SWAP_ENABLED
977 bool "Swap controller enabled by default"
978 depends on MEMCG_SWAP
981 Memory Resource Controller Swap Extension comes with its price in
982 a bigger memory consumption. General purpose distribution kernels
983 which want to enable the feature but keep it disabled by default
984 and let the user enable it by swapaccount=1 boot command line
985 parameter should have this option unselected.
986 For those who want to have the feature enabled by default should
987 select this option (if, for some reason, they need to disable it
988 then swapaccount=0 does the trick).
995 Generic block IO controller cgroup interface. This is the common
996 cgroup interface which should be used by various IO controlling
999 Currently, CFQ IO scheduler uses it to recognize task groups and
1000 control disk bandwidth allocation (proportional time slice allocation)
1001 to such task groups. It is also used by bio throttling logic in
1002 block layer to implement upper limit in IO rates on a device.
1004 This option only enables generic Block IO controller infrastructure.
1005 One needs to also enable actual IO controlling logic/policy. For
1006 enabling proportional weight division of disk bandwidth in CFQ, set
1007 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1008 CONFIG_BLK_DEV_THROTTLING=y.
1010 See Documentation/cgroup-v1/blkio-controller.txt for more information.
1012 config DEBUG_BLK_CGROUP
1013 bool "IO controller debugging"
1014 depends on BLK_CGROUP
1017 Enable some debugging help. Currently it exports additional stat
1018 files in a cgroup which can be useful for debugging.
1020 config CGROUP_WRITEBACK
1022 depends on MEMCG && BLK_CGROUP
1025 menuconfig CGROUP_SCHED
1026 bool "CPU controller"
1029 This feature lets CPU scheduler recognize task groups and control CPU
1030 bandwidth allocation to such task groups. It uses cgroups to group
1034 config FAIR_GROUP_SCHED
1035 bool "Group scheduling for SCHED_OTHER"
1036 depends on CGROUP_SCHED
1037 default CGROUP_SCHED
1039 config CFS_BANDWIDTH
1040 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1041 depends on FAIR_GROUP_SCHED
1044 This option allows users to define CPU bandwidth rates (limits) for
1045 tasks running within the fair group scheduler. Groups with no limit
1046 set are considered to be unconstrained and will run with no
1048 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1050 config RT_GROUP_SCHED
1051 bool "Group scheduling for SCHED_RR/FIFO"
1052 depends on CGROUP_SCHED
1055 This feature lets you explicitly allocate real CPU bandwidth
1056 to task groups. If enabled, it will also make it impossible to
1057 schedule realtime tasks for non-root users until you allocate
1058 realtime bandwidth for them.
1059 See Documentation/scheduler/sched-rt-group.txt for more information.
1064 bool "PIDs controller"
1066 Provides enforcement of process number limits in the scope of a
1067 cgroup. Any attempt to fork more processes than is allowed in the
1068 cgroup will fail. PIDs are fundamentally a global resource because it
1069 is fairly trivial to reach PID exhaustion before you reach even a
1070 conservative kmemcg limit. As a result, it is possible to grind a
1071 system to halt without being limited by other cgroup policies. The
1072 PIDs controller is designed to stop this from happening.
1074 It should be noted that organisational operations (such as attaching
1075 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1076 since the PIDs limit only affects a process's ability to fork, not to
1079 config CGROUP_FREEZER
1080 bool "Freezer controller"
1082 Provides a way to freeze and unfreeze all tasks in a
1085 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1086 controller includes important in-kernel memory consumers per default.
1088 If you're using cgroup2, say N.
1090 config CGROUP_HUGETLB
1091 bool "HugeTLB controller"
1092 depends on HUGETLB_PAGE
1096 Provides a cgroup controller for HugeTLB pages.
1097 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1098 The limit is enforced during page fault. Since HugeTLB doesn't
1099 support page reclaim, enforcing the limit at page fault time implies
1100 that, the application will get SIGBUS signal if it tries to access
1101 HugeTLB pages beyond its limit. This requires the application to know
1102 beforehand how much HugeTLB pages it would require for its use. The
1103 control group is tracked in the third page lru pointer. This means
1104 that we cannot use the controller with huge page less than 3 pages.
1107 bool "Cpuset controller"
1109 This option will let you create and manage CPUSETs which
1110 allow dynamically partitioning a system into sets of CPUs and
1111 Memory Nodes and assigning tasks to run only within those sets.
1112 This is primarily useful on large SMP or NUMA systems.
1116 config PROC_PID_CPUSET
1117 bool "Include legacy /proc/<pid>/cpuset file"
1121 config CGROUP_DEVICE
1122 bool "Device controller"
1124 Provides a cgroup controller implementing whitelists for
1125 devices which a process in the cgroup can mknod or open.
1127 config CGROUP_CPUACCT
1128 bool "Simple CPU accounting controller"
1130 Provides a simple controller for monitoring the
1131 total CPU consumed by the tasks in a cgroup.
1134 bool "Perf controller"
1135 depends on PERF_EVENTS
1137 This option extends the perf per-cpu mode to restrict monitoring
1138 to threads which belong to the cgroup specified and run on the
1144 bool "Support for eBPF programs attached to cgroups"
1145 depends on BPF_SYSCALL
1146 select SOCK_CGROUP_DATA
1148 Allow attaching eBPF programs to a cgroup using the bpf(2)
1149 syscall command BPF_PROG_ATTACH.
1151 In which context these programs are accessed depends on the type
1152 of attachment. For instance, programs that are attached using
1153 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1157 bool "Example controller"
1160 This option enables a simple controller that exports
1161 debugging information about the cgroups framework.
1165 config SOCK_CGROUP_DATA
1171 config CHECKPOINT_RESTORE
1172 bool "Checkpoint/restore support" if EXPERT
1173 select PROC_CHILDREN
1176 Enables additional kernel features in a sake of checkpoint/restore.
1177 In particular it adds auxiliary prctl codes to setup process text,
1178 data and heap segment sizes, and a few additional /proc filesystem
1181 If unsure, say N here.
1183 menuconfig NAMESPACES
1184 bool "Namespaces support" if EXPERT
1185 depends on MULTIUSER
1188 Provides the way to make tasks work with different objects using
1189 the same id. For example same IPC id may refer to different objects
1190 or same user id or pid may refer to different tasks when used in
1191 different namespaces.
1196 bool "UTS namespace"
1199 In this namespace tasks see different info provided with the
1203 bool "IPC namespace"
1204 depends on (SYSVIPC || POSIX_MQUEUE)
1207 In this namespace tasks work with IPC ids which correspond to
1208 different IPC objects in different namespaces.
1211 bool "User namespace"
1214 This allows containers, i.e. vservers, to use user namespaces
1215 to provide different user info for different servers.
1217 When user namespaces are enabled in the kernel it is
1218 recommended that the MEMCG option also be enabled and that
1219 user-space use the memory control groups to limit the amount
1220 of memory a memory unprivileged users can use.
1225 bool "PID Namespaces"
1228 Support process id namespaces. This allows having multiple
1229 processes with the same pid as long as they are in different
1230 pid namespaces. This is a building block of containers.
1233 bool "Network namespace"
1237 Allow user space to create what appear to be multiple instances
1238 of the network stack.
1242 config SCHED_AUTOGROUP
1243 bool "Automatic process group scheduling"
1246 select FAIR_GROUP_SCHED
1248 This option optimizes the scheduler for common desktop workloads by
1249 automatically creating and populating task groups. This separation
1250 of workloads isolates aggressive CPU burners (like build jobs) from
1251 desktop applications. Task group autogeneration is currently based
1254 config SYSFS_DEPRECATED
1255 bool "Enable deprecated sysfs features to support old userspace tools"
1259 This option adds code that switches the layout of the "block" class
1260 devices, to not show up in /sys/class/block/, but only in
1263 This switch is only active when the sysfs.deprecated=1 boot option is
1264 passed or the SYSFS_DEPRECATED_V2 option is set.
1266 This option allows new kernels to run on old distributions and tools,
1267 which might get confused by /sys/class/block/. Since 2007/2008 all
1268 major distributions and tools handle this just fine.
1270 Recent distributions and userspace tools after 2009/2010 depend on
1271 the existence of /sys/class/block/, and will not work with this
1274 Only if you are using a new kernel on an old distribution, you might
1277 config SYSFS_DEPRECATED_V2
1278 bool "Enable deprecated sysfs features by default"
1281 depends on SYSFS_DEPRECATED
1283 Enable deprecated sysfs by default.
1285 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1288 Only if you are using a new kernel on an old distribution, you might
1289 need to say Y here. Even then, odds are you would not need it
1290 enabled, you can always pass the boot option if absolutely necessary.
1293 bool "Kernel->user space relay support (formerly relayfs)"
1296 This option enables support for relay interface support in
1297 certain file systems (such as debugfs).
1298 It is designed to provide an efficient mechanism for tools and
1299 facilities to relay large amounts of data from kernel space to
1304 config BLK_DEV_INITRD
1305 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1306 depends on BROKEN || !FRV
1308 The initial RAM filesystem is a ramfs which is loaded by the
1309 boot loader (loadlin or lilo) and that is mounted as root
1310 before the normal boot procedure. It is typically used to
1311 load modules needed to mount the "real" root file system,
1312 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1314 If RAM disk support (BLK_DEV_RAM) is also included, this
1315 also enables initial RAM disk (initrd) support and adds
1316 15 Kbytes (more on some other architectures) to the kernel size.
1322 source "usr/Kconfig"
1327 prompt "Compiler optimization level"
1328 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1330 config CC_OPTIMIZE_FOR_PERFORMANCE
1331 bool "Optimize for performance"
1333 This is the default optimization level for the kernel, building
1334 with the "-O2" compiler flag for best performance and most
1335 helpful compile-time warnings.
1337 config CC_OPTIMIZE_FOR_SIZE
1338 bool "Optimize for size"
1340 Enabling this option will pass "-Os" instead of "-O2" to
1341 your compiler resulting in a smaller kernel.
1356 config SYSCTL_EXCEPTION_TRACE
1359 Enable support for /proc/sys/debug/exception-trace.
1361 config SYSCTL_ARCH_UNALIGN_NO_WARN
1364 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1365 Allows arch to define/use @no_unaligned_warning to possibly warn
1366 about unaligned access emulation going on under the hood.
1368 config SYSCTL_ARCH_UNALIGN_ALLOW
1371 Enable support for /proc/sys/kernel/unaligned-trap
1372 Allows arches to define/use @unaligned_enabled to runtime toggle
1373 the unaligned access emulation.
1374 see arch/parisc/kernel/unaligned.c for reference
1376 config HAVE_PCSPKR_PLATFORM
1379 # interpreter that classic socket filters depend on
1384 bool "Configure standard kernel features (expert users)"
1385 # Unhide debug options, to make the on-by-default options visible
1388 This option allows certain base kernel options and settings
1389 to be disabled or tweaked. This is for specialized
1390 environments which can tolerate a "non-standard" kernel.
1391 Only use this if you really know what you are doing.
1394 bool "Enable 16-bit UID system calls" if EXPERT
1395 depends on HAVE_UID16 && MULTIUSER
1398 This enables the legacy 16-bit UID syscall wrappers.
1401 bool "Multiple users, groups and capabilities support" if EXPERT
1404 This option enables support for non-root users, groups and
1407 If you say N here, all processes will run with UID 0, GID 0, and all
1408 possible capabilities. Saying N here also compiles out support for
1409 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1412 If unsure, say Y here.
1414 config SGETMASK_SYSCALL
1415 bool "sgetmask/ssetmask syscalls support" if EXPERT
1416 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1418 sys_sgetmask and sys_ssetmask are obsolete system calls
1419 no longer supported in libc but still enabled by default in some
1422 If unsure, leave the default option here.
1424 config SYSFS_SYSCALL
1425 bool "Sysfs syscall support" if EXPERT
1428 sys_sysfs is an obsolete system call no longer supported in libc.
1429 Note that disabling this option is more secure but might break
1430 compatibility with some systems.
1432 If unsure say Y here.
1434 config SYSCTL_SYSCALL
1435 bool "Sysctl syscall support" if EXPERT
1436 depends on PROC_SYSCTL
1440 sys_sysctl uses binary paths that have been found challenging
1441 to properly maintain and use. The interface in /proc/sys
1442 using paths with ascii names is now the primary path to this
1445 Almost nothing using the binary sysctl interface so if you are
1446 trying to save some space it is probably safe to disable this,
1447 making your kernel marginally smaller.
1449 If unsure say N here.
1452 bool "Posix Clocks & timers" if EXPERT
1455 This includes native support for POSIX timers to the kernel.
1456 Some embedded systems have no use for them and therefore they
1457 can be configured out to reduce the size of the kernel image.
1459 When this option is disabled, the following syscalls won't be
1460 available: timer_create, timer_gettime: timer_getoverrun,
1461 timer_settime, timer_delete, clock_adjtime, getitimer,
1462 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1463 clock_getres and clock_nanosleep syscalls will be limited to
1464 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1469 bool "Load all symbols for debugging/ksymoops" if EXPERT
1472 Say Y here to let the kernel print out symbolic crash information and
1473 symbolic stack backtraces. This increases the size of the kernel
1474 somewhat, as all symbols have to be loaded into the kernel image.
1477 bool "Include all symbols in kallsyms"
1478 depends on DEBUG_KERNEL && KALLSYMS
1480 Normally kallsyms only contains the symbols of functions for nicer
1481 OOPS messages and backtraces (i.e., symbols from the text and inittext
1482 sections). This is sufficient for most cases. And only in very rare
1483 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1484 names of variables from the data sections, etc).
1486 This option makes sure that all symbols are loaded into the kernel
1487 image (i.e., symbols from all sections) in cost of increased kernel
1488 size (depending on the kernel configuration, it may be 300KiB or
1489 something like this).
1491 Say N unless you really need all symbols.
1493 config KALLSYMS_ABSOLUTE_PERCPU
1496 default X86_64 && SMP
1498 config KALLSYMS_BASE_RELATIVE
1501 default !IA64 && !(TILE && 64BIT)
1503 Instead of emitting them as absolute values in the native word size,
1504 emit the symbol references in the kallsyms table as 32-bit entries,
1505 each containing a relative value in the range [base, base + U32_MAX]
1506 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1507 an absolute value in the range [0, S32_MAX] or a relative value in the
1508 range [base, base + S32_MAX], where base is the lowest relative symbol
1509 address encountered in the image.
1511 On 64-bit builds, this reduces the size of the address table by 50%,
1512 but more importantly, it results in entries whose values are build
1513 time constants, and no relocation pass is required at runtime to fix
1514 up the entries based on the runtime load address of the kernel.
1518 bool "Enable support for printk" if EXPERT
1521 This option enables normal printk support. Removing it
1522 eliminates most of the message strings from the kernel image
1523 and makes the kernel more or less silent. As this makes it
1524 very difficult to diagnose system problems, saying N here is
1525 strongly discouraged.
1533 bool "BUG() support" if EXPERT
1536 Disabling this option eliminates support for BUG and WARN, reducing
1537 the size of your kernel image and potentially quietly ignoring
1538 numerous fatal conditions. You should only consider disabling this
1539 option for embedded systems with no facilities for reporting errors.
1545 bool "Enable ELF core dumps" if EXPERT
1547 Enable support for generating core dumps. Disabling saves about 4k.
1550 config PCSPKR_PLATFORM
1551 bool "Enable PC-Speaker support" if EXPERT
1552 depends on HAVE_PCSPKR_PLATFORM
1556 This option allows to disable the internal PC-Speaker
1557 support, saving some memory.
1561 bool "Enable full-sized data structures for core" if EXPERT
1563 Disabling this option reduces the size of miscellaneous core
1564 kernel data structures. This saves memory on small machines,
1565 but may reduce performance.
1568 bool "Enable futex support" if EXPERT
1572 Disabling this option will cause the kernel to be built without
1573 support for "fast userspace mutexes". The resulting kernel may not
1574 run glibc-based applications correctly.
1576 config HAVE_FUTEX_CMPXCHG
1580 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1581 is implemented and always working. This removes a couple of runtime
1585 bool "Enable eventpoll support" if EXPERT
1589 Disabling this option will cause the kernel to be built without
1590 support for epoll family of system calls.
1593 bool "Enable signalfd() system call" if EXPERT
1597 Enable the signalfd() system call that allows to receive signals
1598 on a file descriptor.
1603 bool "Enable timerfd() system call" if EXPERT
1607 Enable the timerfd() system call that allows to receive timer
1608 events on a file descriptor.
1613 bool "Enable eventfd() system call" if EXPERT
1617 Enable the eventfd() system call that allows to receive both
1618 kernel notification (ie. KAIO) or userspace notifications.
1622 # syscall, maps, verifier
1624 bool "Enable bpf() system call"
1629 Enable the bpf() system call that allows to manipulate eBPF
1630 programs and maps via file descriptors.
1633 bool "Use full shmem filesystem" if EXPERT
1637 The shmem is an internal filesystem used to manage shared memory.
1638 It is backed by swap and manages resource limits. It is also exported
1639 to userspace as tmpfs if TMPFS is enabled. Disabling this
1640 option replaces shmem and tmpfs with the much simpler ramfs code,
1641 which may be appropriate on small systems without swap.
1644 bool "Enable AIO support" if EXPERT
1647 This option enables POSIX asynchronous I/O which may by used
1648 by some high performance threaded applications. Disabling
1649 this option saves about 7k.
1651 config ADVISE_SYSCALLS
1652 bool "Enable madvise/fadvise syscalls" if EXPERT
1655 This option enables the madvise and fadvise syscalls, used by
1656 applications to advise the kernel about their future memory or file
1657 usage, improving performance. If building an embedded system where no
1658 applications use these syscalls, you can disable this option to save
1662 bool "Enable userfaultfd() system call"
1666 Enable the userfaultfd() system call that allows to intercept and
1667 handle page faults in userland.
1671 bool "Enable PCI quirk workarounds" if EXPERT
1674 This enables workarounds for various PCI chipset
1675 bugs/quirks. Disable this only if your target machine is
1676 unaffected by PCI quirks.
1679 bool "Enable membarrier() system call" if EXPERT
1682 Enable the membarrier() system call that allows issuing memory
1683 barriers across all running threads, which can be used to distribute
1684 the cost of user-space memory barriers asymmetrically by transforming
1685 pairs of memory barriers into pairs consisting of membarrier() and a
1691 bool "Embedded system"
1692 option allnoconfig_y
1695 This option should be enabled if compiling the kernel for
1696 an embedded system so certain expert options are available
1699 config HAVE_PERF_EVENTS
1702 See tools/perf/design.txt for details.
1704 config PERF_USE_VMALLOC
1707 See tools/perf/design.txt for details
1709 menu "Kernel Performance Events And Counters"
1712 bool "Kernel performance events and counters"
1713 default y if PROFILING
1714 depends on HAVE_PERF_EVENTS
1719 Enable kernel support for various performance events provided
1720 by software and hardware.
1722 Software events are supported either built-in or via the
1723 use of generic tracepoints.
1725 Most modern CPUs support performance events via performance
1726 counter registers. These registers count the number of certain
1727 types of hw events: such as instructions executed, cachemisses
1728 suffered, or branches mis-predicted - without slowing down the
1729 kernel or applications. These registers can also trigger interrupts
1730 when a threshold number of events have passed - and can thus be
1731 used to profile the code that runs on that CPU.
1733 The Linux Performance Event subsystem provides an abstraction of
1734 these software and hardware event capabilities, available via a
1735 system call and used by the "perf" utility in tools/perf/. It
1736 provides per task and per CPU counters, and it provides event
1737 capabilities on top of those.
1741 config DEBUG_PERF_USE_VMALLOC
1743 bool "Debug: use vmalloc to back perf mmap() buffers"
1744 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1745 select PERF_USE_VMALLOC
1747 Use vmalloc memory to back perf mmap() buffers.
1749 Mostly useful for debugging the vmalloc code on platforms
1750 that don't require it.
1756 config VM_EVENT_COUNTERS
1758 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1760 VM event counters are needed for event counts to be shown.
1761 This option allows the disabling of the VM event counters
1762 on EXPERT systems. /proc/vmstat will only show page counts
1763 if VM event counters are disabled.
1767 bool "Enable SLUB debugging support" if EXPERT
1768 depends on SLUB && SYSFS
1770 SLUB has extensive debug support features. Disabling these can
1771 result in significant savings in code size. This also disables
1772 SLUB sysfs support. /sys/slab will not exist and there will be
1773 no support for cache validation etc.
1776 bool "Disable heap randomization"
1779 Randomizing heap placement makes heap exploits harder, but it
1780 also breaks ancient binaries (including anything libc5 based).
1781 This option changes the bootup default to heap randomization
1782 disabled, and can be overridden at runtime by setting
1783 /proc/sys/kernel/randomize_va_space to 2.
1785 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1788 prompt "Choose SLAB allocator"
1791 This option allows to select a slab allocator.
1795 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1797 The regular slab allocator that is established and known to work
1798 well in all environments. It organizes cache hot objects in
1799 per cpu and per node queues.
1802 bool "SLUB (Unqueued Allocator)"
1803 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1805 SLUB is a slab allocator that minimizes cache line usage
1806 instead of managing queues of cached objects (SLAB approach).
1807 Per cpu caching is realized using slabs of objects instead
1808 of queues of objects. SLUB can use memory efficiently
1809 and has enhanced diagnostics. SLUB is the default choice for
1814 bool "SLOB (Simple Allocator)"
1816 SLOB replaces the stock allocator with a drastically simpler
1817 allocator. SLOB is generally more space efficient but
1818 does not perform as well on large systems.
1822 config SLAB_FREELIST_RANDOM
1824 depends on SLAB || SLUB
1825 bool "SLAB freelist randomization"
1827 Randomizes the freelist order used on creating new pages. This
1828 security feature reduces the predictability of the kernel slab
1829 allocator against heap overflows.
1831 config SLUB_CPU_PARTIAL
1833 depends on SLUB && SMP
1834 bool "SLUB per cpu partial cache"
1836 Per cpu partial caches accellerate objects allocation and freeing
1837 that is local to a processor at the price of more indeterminism
1838 in the latency of the free. On overflow these caches will be cleared
1839 which requires the taking of locks that may cause latency spikes.
1840 Typically one would choose no for a realtime system.
1842 config MMAP_ALLOW_UNINITIALIZED
1843 bool "Allow mmapped anonymous memory to be uninitialized"
1844 depends on EXPERT && !MMU
1847 Normally, and according to the Linux spec, anonymous memory obtained
1848 from mmap() has it's contents cleared before it is passed to
1849 userspace. Enabling this config option allows you to request that
1850 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1851 providing a huge performance boost. If this option is not enabled,
1852 then the flag will be ignored.
1854 This is taken advantage of by uClibc's malloc(), and also by
1855 ELF-FDPIC binfmt's brk and stack allocator.
1857 Because of the obvious security issues, this option should only be
1858 enabled on embedded devices where you control what is run in
1859 userspace. Since that isn't generally a problem on no-MMU systems,
1860 it is normally safe to say Y here.
1862 See Documentation/nommu-mmap.txt for more information.
1864 config SYSTEM_DATA_VERIFICATION
1866 select SYSTEM_TRUSTED_KEYRING
1870 select ASYMMETRIC_KEY_TYPE
1871 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1874 select X509_CERTIFICATE_PARSER
1875 select PKCS7_MESSAGE_PARSER
1877 Provide PKCS#7 message verification using the contents of the system
1878 trusted keyring to provide public keys. This then can be used for
1879 module verification, kexec image verification and firmware blob
1883 bool "Profiling support"
1885 Say Y here to enable the extended profiling support mechanisms used
1886 by profilers such as OProfile.
1889 # Place an empty function call at each tracepoint site. Can be
1890 # dynamically changed for a probe function.
1895 source "arch/Kconfig"
1897 endmenu # General setup
1899 config HAVE_GENERIC_DMA_COHERENT
1906 depends on SLAB || SLUB_DEBUG
1914 default 0 if BASE_FULL
1915 default 1 if !BASE_FULL
1918 bool "Enable loadable module support"
1921 Kernel modules are small pieces of compiled code which can
1922 be inserted in the running kernel, rather than being
1923 permanently built into the kernel. You use the "modprobe"
1924 tool to add (and sometimes remove) them. If you say Y here,
1925 many parts of the kernel can be built as modules (by
1926 answering M instead of Y where indicated): this is most
1927 useful for infrequently used options which are not required
1928 for booting. For more information, see the man pages for
1929 modprobe, lsmod, modinfo, insmod and rmmod.
1931 If you say Y here, you will need to run "make
1932 modules_install" to put the modules under /lib/modules/
1933 where modprobe can find them (you may need to be root to do
1940 config MODULE_FORCE_LOAD
1941 bool "Forced module loading"
1944 Allow loading of modules without version information (ie. modprobe
1945 --force). Forced module loading sets the 'F' (forced) taint flag and
1946 is usually a really bad idea.
1948 config MODULE_UNLOAD
1949 bool "Module unloading"
1951 Without this option you will not be able to unload any
1952 modules (note that some modules may not be unloadable
1953 anyway), which makes your kernel smaller, faster
1954 and simpler. If unsure, say Y.
1956 config MODULE_FORCE_UNLOAD
1957 bool "Forced module unloading"
1958 depends on MODULE_UNLOAD
1960 This option allows you to force a module to unload, even if the
1961 kernel believes it is unsafe: the kernel will remove the module
1962 without waiting for anyone to stop using it (using the -f option to
1963 rmmod). This is mainly for kernel developers and desperate users.
1967 bool "Module versioning support"
1969 Usually, you have to use modules compiled with your kernel.
1970 Saying Y here makes it sometimes possible to use modules
1971 compiled for different kernels, by adding enough information
1972 to the modules to (hopefully) spot any changes which would
1973 make them incompatible with the kernel you are running. If
1976 config MODULE_REL_CRCS
1978 depends on MODVERSIONS
1980 config MODULE_SRCVERSION_ALL
1981 bool "Source checksum for all modules"
1983 Modules which contain a MODULE_VERSION get an extra "srcversion"
1984 field inserted into their modinfo section, which contains a
1985 sum of the source files which made it. This helps maintainers
1986 see exactly which source was used to build a module (since
1987 others sometimes change the module source without updating
1988 the version). With this option, such a "srcversion" field
1989 will be created for all modules. If unsure, say N.
1992 bool "Module signature verification"
1994 select SYSTEM_DATA_VERIFICATION
1996 Check modules for valid signatures upon load: the signature
1997 is simply appended to the module. For more information see
1998 Documentation/module-signing.txt.
2000 Note that this option adds the OpenSSL development packages as a
2001 kernel build dependency so that the signing tool can use its crypto
2004 !!!WARNING!!! If you enable this option, you MUST make sure that the
2005 module DOES NOT get stripped after being signed. This includes the
2006 debuginfo strip done by some packagers (such as rpmbuild) and
2007 inclusion into an initramfs that wants the module size reduced.
2009 config MODULE_SIG_FORCE
2010 bool "Require modules to be validly signed"
2011 depends on MODULE_SIG
2013 Reject unsigned modules or signed modules for which we don't have a
2014 key. Without this, such modules will simply taint the kernel.
2016 config MODULE_SIG_ALL
2017 bool "Automatically sign all modules"
2019 depends on MODULE_SIG
2021 Sign all modules during make modules_install. Without this option,
2022 modules must be signed manually, using the scripts/sign-file tool.
2024 comment "Do not forget to sign required modules with scripts/sign-file"
2025 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2028 prompt "Which hash algorithm should modules be signed with?"
2029 depends on MODULE_SIG
2031 This determines which sort of hashing algorithm will be used during
2032 signature generation. This algorithm _must_ be built into the kernel
2033 directly so that signature verification can take place. It is not
2034 possible to load a signed module containing the algorithm to check
2035 the signature on that module.
2037 config MODULE_SIG_SHA1
2038 bool "Sign modules with SHA-1"
2041 config MODULE_SIG_SHA224
2042 bool "Sign modules with SHA-224"
2043 select CRYPTO_SHA256
2045 config MODULE_SIG_SHA256
2046 bool "Sign modules with SHA-256"
2047 select CRYPTO_SHA256
2049 config MODULE_SIG_SHA384
2050 bool "Sign modules with SHA-384"
2051 select CRYPTO_SHA512
2053 config MODULE_SIG_SHA512
2054 bool "Sign modules with SHA-512"
2055 select CRYPTO_SHA512
2059 config MODULE_SIG_HASH
2061 depends on MODULE_SIG
2062 default "sha1" if MODULE_SIG_SHA1
2063 default "sha224" if MODULE_SIG_SHA224
2064 default "sha256" if MODULE_SIG_SHA256
2065 default "sha384" if MODULE_SIG_SHA384
2066 default "sha512" if MODULE_SIG_SHA512
2068 config MODULE_COMPRESS
2069 bool "Compress modules on installation"
2073 Compresses kernel modules when 'make modules_install' is run; gzip or
2074 xz depending on "Compression algorithm" below.
2076 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2078 Out-of-tree kernel modules installed using Kbuild will also be
2079 compressed upon installation.
2081 Note: for modules inside an initrd or initramfs, it's more efficient
2082 to compress the whole initrd or initramfs instead.
2084 Note: This is fully compatible with signed modules.
2089 prompt "Compression algorithm"
2090 depends on MODULE_COMPRESS
2091 default MODULE_COMPRESS_GZIP
2093 This determines which sort of compression will be used during
2094 'make modules_install'.
2096 GZIP (default) and XZ are supported.
2098 config MODULE_COMPRESS_GZIP
2101 config MODULE_COMPRESS_XZ
2106 config TRIM_UNUSED_KSYMS
2107 bool "Trim unused exported kernel symbols"
2108 depends on MODULES && !UNUSED_SYMBOLS
2110 The kernel and some modules make many symbols available for
2111 other modules to use via EXPORT_SYMBOL() and variants. Depending
2112 on the set of modules being selected in your kernel configuration,
2113 many of those exported symbols might never be used.
2115 This option allows for unused exported symbols to be dropped from
2116 the build. In turn, this provides the compiler more opportunities
2117 (especially when using LTO) for optimizing the code and reducing
2118 binary size. This might have some security advantages as well.
2120 If unsure, or if you need to build out-of-tree modules, say N.
2124 config MODULES_TREE_LOOKUP
2126 depends on PERF_EVENTS || TRACING
2128 config INIT_ALL_POSSIBLE
2131 Back when each arch used to define their own cpu_online_mask and
2132 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2133 with all 1s, and others with all 0s. When they were centralised,
2134 it was better to provide this option than to break all the archs
2135 and have several arch maintainers pursuing me down dark alleys.
2137 source "block/Kconfig"
2139 config PREEMPT_NOTIFIERS
2149 Build a simple ASN.1 grammar compiler that produces a bytecode output
2150 that can be interpreted by the ASN.1 stream decoder and used to
2151 inform it as to what tags are to be expected in a stream and what
2152 functions to call on what tags.
2154 source "kernel/Kconfig.locks"
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