Version:  2.0.40 2.2.26 2.4.37 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4


  1 config ARCH
  2         string
  3         option env="ARCH"
  6         string
  7         option env="KERNELVERSION"
 10         string
 11         depends on !UML
 12         option defconfig_list
 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"
 20         bool
 21         depends on !UML
 23 config IRQ_WORK
 24         bool
 27         bool
 29 menu "General setup"
 31 config BROKEN
 32         bool
 34 config BROKEN_ON_SMP
 35         bool
 36         depends on BROKEN || !SMP
 37         default y
 40         int
 41         default 32 if !UML
 42         default 128 if UML
 43         help
 44           Maximum of each of the number of arguments and environment
 45           variables passed to init from the kernel command line.
 48 config CROSS_COMPILE
 49         string "Cross-compiler tool prefix"
 50         help
 51           Same as running 'make CROSS_COMPILE=prefix-' but stored for
 52           default make runs in this kernel build directory.  You don't
 53           need to set this unless you want the configured kernel build
 54           directory to select the cross-compiler automatically.
 56 config COMPILE_TEST
 57         bool "Compile also drivers which will not load"
 58         default n
 59         help
 60           Some drivers can be compiled on a different platform than they are
 61           intended to be run on. Despite they cannot be loaded there (or even
 62           when they load they cannot be used due to missing HW support),
 63           developers still, opposing to distributors, might want to build such
 64           drivers to compile-test them.
 66           If you are a developer and want to build everything available, say Y
 67           here. If you are a user/distributor, say N here to exclude useless
 68           drivers to be distributed.
 71         string "Local version - append to kernel release"
 72         help
 73           Append an extra string to the end of your kernel version.
 74           This will show up when you type uname, for example.
 75           The string you set here will be appended after the contents of
 76           any files with a filename matching localversion* in your
 77           object and source tree, in that order.  Your total string can
 78           be a maximum of 64 characters.
 81         bool "Automatically append version information to the version string"
 82         default y
 83         help
 84           This will try to automatically determine if the current tree is a
 85           release tree by looking for git tags that belong to the current
 86           top of tree revision.
 88           A string of the format -gxxxxxxxx will be added to the localversion
 89           if a git-based tree is found.  The string generated by this will be
 90           appended after any matching localversion* files, and after the value
 91           set in CONFIG_LOCALVERSION.
 93           (The actual string used here is the first eight characters produced
 94           by running the command:
 96             $ git rev-parse --verify HEAD
 98           which is done within the script "scripts/setlocalversion".)
101         bool
103 config HAVE_KERNEL_BZIP2
104         bool
107         bool
109 config HAVE_KERNEL_XZ
110         bool
112 config HAVE_KERNEL_LZO
113         bool
115 config HAVE_KERNEL_LZ4
116         bool
118 choice
119         prompt "Kernel compression mode"
120         default KERNEL_GZIP
122         help
123           The linux kernel is a kind of self-extracting executable.
124           Several compression algorithms are available, which differ
125           in efficiency, compression and decompression speed.
126           Compression speed is only relevant when building a kernel.
127           Decompression speed is relevant at each boot.
129           If you have any problems with bzip2 or lzma compressed
130           kernels, mail me (Alain Knaff) <>. (An older
131           version of this functionality (bzip2 only), for 2.4, was
132           supplied by Christian Ludwig)
134           High compression options are mostly useful for users, who
135           are low on disk space (embedded systems), but for whom ram
136           size matters less.
138           If in doubt, select 'gzip'
140 config KERNEL_GZIP
141         bool "Gzip"
142         depends on HAVE_KERNEL_GZIP
143         help
144           The old and tried gzip compression. It provides a good balance
145           between compression ratio and decompression speed.
147 config KERNEL_BZIP2
148         bool "Bzip2"
149         depends on HAVE_KERNEL_BZIP2
150         help
151           Its compression ratio and speed is intermediate.
152           Decompression speed is slowest among the choices.  The kernel
153           size is about 10% smaller with bzip2, in comparison to gzip.
154           Bzip2 uses a large amount of memory. For modern kernels you
155           will need at least 8MB RAM or more for booting.
157 config KERNEL_LZMA
158         bool "LZMA"
159         depends on HAVE_KERNEL_LZMA
160         help
161           This compression algorithm's ratio is best.  Decompression speed
162           is between gzip and bzip2.  Compression is slowest.
163           The kernel size is about 33% smaller with LZMA in comparison to gzip.
165 config KERNEL_XZ
166         bool "XZ"
167         depends on HAVE_KERNEL_XZ
168         help
169           XZ uses the LZMA2 algorithm and instruction set specific
170           BCJ filters which can improve compression ratio of executable
171           code. The size of the kernel is about 30% smaller with XZ in
172           comparison to gzip. On architectures for which there is a BCJ
173           filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
174           will create a few percent smaller kernel than plain LZMA.
176           The speed is about the same as with LZMA: The decompression
177           speed of XZ is better than that of bzip2 but worse than gzip
178           and LZO. Compression is slow.
180 config KERNEL_LZO
181         bool "LZO"
182         depends on HAVE_KERNEL_LZO
183         help
184           Its compression ratio is the poorest among the choices. The kernel
185           size is about 10% bigger than gzip; however its speed
186           (both compression and decompression) is the fastest.
188 config KERNEL_LZ4
189         bool "LZ4"
190         depends on HAVE_KERNEL_LZ4
191         help
192           LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
193           A preliminary version of LZ4 de/compression tool is available at
194           <>.
196           Its compression ratio is worse than LZO. The size of the kernel
197           is about 8% bigger than LZO. But the decompression speed is
198           faster than LZO.
200 endchoice
203         string "Default hostname"
204         default "(none)"
205         help
206           This option determines the default system hostname before userspace
207           calls sethostname(2). The kernel traditionally uses "(none)" here,
208           but you may wish to use a different default here to make a minimal
209           system more usable with less configuration.
211 config SWAP
212         bool "Support for paging of anonymous memory (swap)"
213         depends on MMU && BLOCK
214         default y
215         help
216           This option allows you to choose whether you want to have support
217           for so called swap devices or swap files in your kernel that are
218           used to provide more virtual memory than the actual RAM present
219           in your computer.  If unsure say Y.
221 config SYSVIPC
222         bool "System V IPC"
223         ---help---
224           Inter Process Communication is a suite of library functions and
225           system calls which let processes (running programs) synchronize and
226           exchange information. It is generally considered to be a good thing,
227           and some programs won't run unless you say Y here. In particular, if
228           you want to run the DOS emulator dosemu under Linux (read the
229           DOSEMU-HOWTO, available from <>),
230           you'll need to say Y here.
232           You can find documentation about IPC with "info ipc" and also in
233           section 6.4 of the Linux Programmer's Guide, available from
234           <>.
237         bool
238         depends on SYSVIPC
239         depends on SYSCTL
240         default y
242 config POSIX_MQUEUE
243         bool "POSIX Message Queues"
244         depends on NET
245         ---help---
246           POSIX variant of message queues is a part of IPC. In POSIX message
247           queues every message has a priority which decides about succession
248           of receiving it by a process. If you want to compile and run
249           programs written e.g. for Solaris with use of its POSIX message
250           queues (functions mq_*) say Y here.
252           POSIX message queues are visible as a filesystem called 'mqueue'
253           and can be mounted somewhere if you want to do filesystem
254           operations on message queues.
256           If unsure, say Y.
259         bool
260         depends on POSIX_MQUEUE
261         depends on SYSCTL
262         default y
265         bool "Enable process_vm_readv/writev syscalls"
266         depends on MMU
267         default y
268         help
269           Enabling this option adds the system calls process_vm_readv and
270           process_vm_writev which allow a process with the correct privileges
271           to directly read from or write to another process' address space.
272           See the man page for more details.
274 config FHANDLE
275         bool "open by fhandle syscalls"
276         select EXPORTFS
277         help
278           If you say Y here, a user level program will be able to map
279           file names to handle and then later use the handle for
280           different file system operations. This is useful in implementing
281           userspace file servers, which now track files using handles instead
282           of names. The handle would remain the same even if file names
283           get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
284           syscalls.
286 config USELIB
287         bool "uselib syscall"
288         default y
289         help
290           This option enables the uselib syscall, a system call used in the
291           dynamic linker from libc5 and earlier.  glibc does not use this
292           system call.  If you intend to run programs built on libc5 or
293           earlier, you may need to enable this syscall.  Current systems
294           running glibc can safely disable this.
296 config AUDIT
297         bool "Auditing support"
298         depends on NET
299         help
300           Enable auditing infrastructure that can be used with another
301           kernel subsystem, such as SELinux (which requires this for
302           logging of avc messages output).  Does not do system-call
303           auditing without CONFIG_AUDITSYSCALL.
306         bool
309         bool "Enable system-call auditing support"
310         depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
311         default y if SECURITY_SELINUX
312         help
313           Enable low-overhead system-call auditing infrastructure that
314           can be used independently or with another kernel subsystem,
315           such as SELinux.
317 config AUDIT_WATCH
318         def_bool y
319         depends on AUDITSYSCALL
320         select FSNOTIFY
322 config AUDIT_TREE
323         def_bool y
324         depends on AUDITSYSCALL
325         select FSNOTIFY
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
330 menu "CPU/Task time and stats accounting"
333         bool
335 choice
336         prompt "Cputime accounting"
337         default TICK_CPU_ACCOUNTING if !PPC64
338         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
340 # Kind of a stub config for the pure tick based cputime accounting
342         bool "Simple tick based cputime accounting"
343         depends on !S390 && !NO_HZ_FULL
344         help
345           This is the basic tick based cputime accounting that maintains
346           statistics about user, system and idle time spent on per jiffies
347           granularity.
349           If unsure, say Y.
352         bool "Deterministic task and CPU time accounting"
353         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
354         select VIRT_CPU_ACCOUNTING
355         help
356           Select this option to enable more accurate task and CPU time
357           accounting.  This is done by reading a CPU counter on each
358           kernel entry and exit and on transitions within the kernel
359           between system, softirq and hardirq state, so there is a
360           small performance impact.  In the case of s390 or IBM POWER > 5,
361           this also enables accounting of stolen time on logically-partitioned
362           systems.
365         bool "Full dynticks CPU time accounting"
366         depends on HAVE_CONTEXT_TRACKING
367         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
368         select VIRT_CPU_ACCOUNTING
369         select CONTEXT_TRACKING
370         help
371           Select this option to enable task and CPU time accounting on full
372           dynticks systems. This accounting is implemented by watching every
373           kernel-user boundaries using the context tracking subsystem.
374           The accounting is thus performed at the expense of some significant
375           overhead.
377           For now this is only useful if you are working on the full
378           dynticks subsystem development.
380           If unsure, say N.
383         bool "Fine granularity task level IRQ time accounting"
384         depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
385         help
386           Select this option to enable fine granularity task irq time
387           accounting. This is done by reading a timestamp on each
388           transitions between softirq and hardirq state, so there can be a
389           small performance impact.
391           If in doubt, say N here.
393 endchoice
396         bool "BSD Process Accounting"
397         depends on MULTIUSER
398         help
399           If you say Y here, a user level program will be able to instruct the
400           kernel (via a special system call) to write process accounting
401           information to a file: whenever a process exits, information about
402           that process will be appended to the file by the kernel.  The
403           information includes things such as creation time, owning user,
404           command name, memory usage, controlling terminal etc. (the complete
405           list is in the struct acct in <file:include/linux/acct.h>).  It is
406           up to the user level program to do useful things with this
407           information.  This is generally a good idea, so say Y.
409 config BSD_PROCESS_ACCT_V3
410         bool "BSD Process Accounting version 3 file format"
411         depends on BSD_PROCESS_ACCT
412         default n
413         help
414           If you say Y here, the process accounting information is written
415           in a new file format that also logs the process IDs of each
416           process and it's parent. Note that this file format is incompatible
417           with previous v0/v1/v2 file formats, so you will need updated tools
418           for processing it. A preliminary version of these tools is available
419           at <>.
421 config TASKSTATS
422         bool "Export task/process statistics through netlink"
423         depends on NET
424         depends on MULTIUSER
425         default n
426         help
427           Export selected statistics for tasks/processes through the
428           generic netlink interface. Unlike BSD process accounting, the
429           statistics are available during the lifetime of tasks/processes as
430           responses to commands. Like BSD accounting, they are sent to user
431           space on task exit.
433           Say N if unsure.
435 config TASK_DELAY_ACCT
436         bool "Enable per-task delay accounting"
437         depends on TASKSTATS
438         select SCHED_INFO
439         help
440           Collect information on time spent by a task waiting for system
441           resources like cpu, synchronous block I/O completion and swapping
442           in pages. Such statistics can help in setting a task's priorities
443           relative to other tasks for cpu, io, rss limits etc.
445           Say N if unsure.
447 config TASK_XACCT
448         bool "Enable extended accounting over taskstats"
449         depends on TASKSTATS
450         help
451           Collect extended task accounting data and send the data
452           to userland for processing over the taskstats interface.
454           Say N if unsure.
457         bool "Enable per-task storage I/O accounting"
458         depends on TASK_XACCT
459         help
460           Collect information on the number of bytes of storage I/O which this
461           task has caused.
463           Say N if unsure.
465 endmenu # "CPU/Task time and stats accounting"
467 menu "RCU Subsystem"
469 config TREE_RCU
470         bool
471         default y if !PREEMPT && SMP
472         help
473           This option selects the RCU implementation that is
474           designed for very large SMP system with hundreds or
475           thousands of CPUs.  It also scales down nicely to
476           smaller systems.
478 config PREEMPT_RCU
479         bool
480         default y if PREEMPT
481         help
482           This option selects the RCU implementation that is
483           designed for very large SMP systems with hundreds or
484           thousands of CPUs, but for which real-time response
485           is also required.  It also scales down nicely to
486           smaller systems.
488           Select this option if you are unsure.
490 config TINY_RCU
491         bool
492         default y if !PREEMPT && !SMP
493         help
494           This option selects the RCU implementation that is
495           designed for UP systems from which real-time response
496           is not required.  This option greatly reduces the
497           memory footprint of RCU.
499 config RCU_EXPERT
500         bool "Make expert-level adjustments to RCU configuration"
501         default n
502         help
503           This option needs to be enabled if you wish to make
504           expert-level adjustments to RCU configuration.  By default,
505           no such adjustments can be made, which has the often-beneficial
506           side-effect of preventing "make oldconfig" from asking you all
507           sorts of detailed questions about how you would like numerous
508           obscure RCU options to be set up.
510           Say Y if you need to make expert-level adjustments to RCU.
512           Say N if you are unsure.
514 config SRCU
515         bool
516         help
517           This option selects the sleepable version of RCU. This version
518           permits arbitrary sleeping or blocking within RCU read-side critical
519           sections.
521 config TASKS_RCU
522         bool
523         default n
524         select SRCU
525         help
526           This option enables a task-based RCU implementation that uses
527           only voluntary context switch (not preemption!), idle, and
528           user-mode execution as quiescent states.
531         def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
532         help
533           This option enables RCU CPU stall code that is common between
534           the TINY and TREE variants of RCU.  The purpose is to allow
535           the tiny variants to disable RCU CPU stall warnings, while
536           making these warnings mandatory for the tree variants.
539        bool
542         bool "Force context tracking"
543         depends on CONTEXT_TRACKING
544         default y if !NO_HZ_FULL
545         help
546           The major pre-requirement for full dynticks to work is to
547           support the context tracking subsystem. But there are also
548           other dependencies to provide in order to make the full
549           dynticks working.
551           This option stands for testing when an arch implements the
552           context tracking backend but doesn't yet fullfill all the
553           requirements to make the full dynticks feature working.
554           Without the full dynticks, there is no way to test the support
555           for context tracking and the subsystems that rely on it: RCU
556           userspace extended quiescent state and tickless cputime
557           accounting. This option copes with the absence of the full
558           dynticks subsystem by forcing the context tracking on all
559           CPUs in the system.
561           Say Y only if you're working on the development of an
562           architecture backend for the context tracking.
564           Say N otherwise, this option brings an overhead that you
565           don't want in production.
568 config RCU_FANOUT
569         int "Tree-based hierarchical RCU fanout value"
570         range 2 64 if 64BIT
571         range 2 32 if !64BIT
572         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
573         default 64 if 64BIT
574         default 32 if !64BIT
575         help
576           This option controls the fanout of hierarchical implementations
577           of RCU, allowing RCU to work efficiently on machines with
578           large numbers of CPUs.  This value must be at least the fourth
579           root of NR_CPUS, which allows NR_CPUS to be insanely large.
580           The default value of RCU_FANOUT should be used for production
581           systems, but if you are stress-testing the RCU implementation
582           itself, small RCU_FANOUT values allow you to test large-system
583           code paths on small(er) systems.
585           Select a specific number if testing RCU itself.
586           Take the default if unsure.
588 config RCU_FANOUT_LEAF
589         int "Tree-based hierarchical RCU leaf-level fanout value"
590         range 2 64 if 64BIT
591         range 2 32 if !64BIT
592         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
593         default 16
594         help
595           This option controls the leaf-level fanout of hierarchical
596           implementations of RCU, and allows trading off cache misses
597           against lock contention.  Systems that synchronize their
598           scheduling-clock interrupts for energy-efficiency reasons will
599           want the default because the smaller leaf-level fanout keeps
600           lock contention levels acceptably low.  Very large systems
601           (hundreds or thousands of CPUs) will instead want to set this
602           value to the maximum value possible in order to reduce the
603           number of cache misses incurred during RCU's grace-period
604           initialization.  These systems tend to run CPU-bound, and thus
605           are not helped by synchronized interrupts, and thus tend to
606           skew them, which reduces lock contention enough that large
607           leaf-level fanouts work well.
609           Select a specific number if testing RCU itself.
611           Select the maximum permissible value for large systems.
613           Take the default if unsure.
615 config RCU_FAST_NO_HZ
616         bool "Accelerate last non-dyntick-idle CPU's grace periods"
617         depends on NO_HZ_COMMON && SMP && RCU_EXPERT
618         default n
619         help
620           This option permits CPUs to enter dynticks-idle state even if
621           they have RCU callbacks queued, and prevents RCU from waking
622           these CPUs up more than roughly once every four jiffies (by
623           default, you can adjust this using the rcutree.rcu_idle_gp_delay
624           parameter), thus improving energy efficiency.  On the other
625           hand, this option increases the duration of RCU grace periods,
626           for example, slowing down synchronize_rcu().
628           Say Y if energy efficiency is critically important, and you
629                 don't care about increased grace-period durations.
631           Say N if you are unsure.
633 config TREE_RCU_TRACE
634         def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
635         select DEBUG_FS
636         help
637           This option provides tracing for the TREE_RCU and
638           PREEMPT_RCU implementations, permitting Makefile to
639           trivially select kernel/rcutree_trace.c.
641 config RCU_BOOST
642         bool "Enable RCU priority boosting"
643         depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
644         default n
645         help
646           This option boosts the priority of preempted RCU readers that
647           block the current preemptible RCU grace period for too long.
648           This option also prevents heavy loads from blocking RCU
649           callback invocation for all flavors of RCU.
651           Say Y here if you are working with real-time apps or heavy loads
652           Say N here if you are unsure.
655         int "Real-time priority to use for RCU worker threads"
656         range 1 99 if RCU_BOOST
657         range 0 99 if !RCU_BOOST
658         default 1 if RCU_BOOST
659         default 0 if !RCU_BOOST
660         depends on RCU_EXPERT
661         help
662           This option specifies the SCHED_FIFO priority value that will be
663           assigned to the rcuc/n and rcub/n threads and is also the value
664           used for RCU_BOOST (if enabled). If you are working with a
665           real-time application that has one or more CPU-bound threads
666           running at a real-time priority level, you should set
667           RCU_KTHREAD_PRIO to a priority higher than the highest-priority
668           real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO
669           value of 1 is appropriate in the common case, which is real-time
670           applications that do not have any CPU-bound threads.
672           Some real-time applications might not have a single real-time
673           thread that saturates a given CPU, but instead might have
674           multiple real-time threads that, taken together, fully utilize
675           that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
676           a priority higher than the lowest-priority thread that is
677           conspiring to prevent the CPU from running any non-real-time
678           tasks.  For example, if one thread at priority 10 and another
679           thread at priority 5 are between themselves fully consuming
680           the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
681           set to priority 6 or higher.
683           Specify the real-time priority, or take the default if unsure.
685 config RCU_BOOST_DELAY
686         int "Milliseconds to delay boosting after RCU grace-period start"
687         range 0 3000
688         depends on RCU_BOOST
689         default 500
690         help
691           This option specifies the time to wait after the beginning of
692           a given grace period before priority-boosting preempted RCU
693           readers blocking that grace period.  Note that any RCU reader
694           blocking an expedited RCU grace period is boosted immediately.
696           Accept the default if unsure.
698 config RCU_NOCB_CPU
699         bool "Offload RCU callback processing from boot-selected CPUs"
700         depends on TREE_RCU || PREEMPT_RCU
701         depends on RCU_EXPERT || NO_HZ_FULL
702         default n
703         help
704           Use this option to reduce OS jitter for aggressive HPC or
705           real-time workloads.  It can also be used to offload RCU
706           callback invocation to energy-efficient CPUs in battery-powered
707           asymmetric multiprocessors.
709           This option offloads callback invocation from the set of
710           CPUs specified at boot time by the rcu_nocbs parameter.
711           For each such CPU, a kthread ("rcuox/N") will be created to
712           invoke callbacks, where the "N" is the CPU being offloaded,
713           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
714           "s" for RCU-sched.  Nothing prevents this kthread from running
715           on the specified CPUs, but (1) the kthreads may be preempted
716           between each callback, and (2) affinity or cgroups can be used
717           to force the kthreads to run on whatever set of CPUs is desired.
719           Say Y here if you want to help to debug reduced OS jitter.
720           Say N here if you are unsure.
722 choice
723         prompt "Build-forced no-CBs CPUs"
724         default RCU_NOCB_CPU_NONE
725         depends on RCU_NOCB_CPU
726         help
727           This option allows no-CBs CPUs (whose RCU callbacks are invoked
728           from kthreads rather than from softirq context) to be specified
729           at build time.  Additional no-CBs CPUs may be specified by
730           the rcu_nocbs= boot parameter.
732 config RCU_NOCB_CPU_NONE
733         bool "No build_forced no-CBs CPUs"
734         help
735           This option does not force any of the CPUs to be no-CBs CPUs.
736           Only CPUs designated by the rcu_nocbs= boot parameter will be
737           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
738           kthreads whose names begin with "rcuo".  All other CPUs will
739           invoke their own RCU callbacks in softirq context.
741           Select this option if you want to choose no-CBs CPUs at
742           boot time, for example, to allow testing of different no-CBs
743           configurations without having to rebuild the kernel each time.
745 config RCU_NOCB_CPU_ZERO
746         bool "CPU 0 is a build_forced no-CBs CPU"
747         help
748           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
749           callbacks are invoked by a per-CPU kthread whose name begins
750           with "rcuo".  Additional CPUs may be designated as no-CBs
751           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
752           All other CPUs will invoke their own RCU callbacks in softirq
753           context.
755           Select this if CPU 0 needs to be a no-CBs CPU for real-time
756           or energy-efficiency reasons, but the real reason it exists
757           is to ensure that randconfig testing covers mixed systems.
759 config RCU_NOCB_CPU_ALL
760         bool "All CPUs are build_forced no-CBs CPUs"
761         help
762           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
763           boot parameter will be ignored.  All CPUs' RCU callbacks will
764           be executed in the context of per-CPU rcuo kthreads created for
765           this purpose.  Assuming that the kthreads whose names start with
766           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
767           on the remaining CPUs, but might decrease memory locality during
768           RCU-callback invocation, thus potentially degrading throughput.
770           Select this if all CPUs need to be no-CBs CPUs for real-time
771           or energy-efficiency reasons.
773 endchoice
776         bool
777         default n
778         help
779           This option enables expedited grace periods at boot time,
780           as if rcu_expedite_gp() had been invoked early in boot.
781           The corresponding rcu_unexpedite_gp() is invoked from
782           rcu_end_inkernel_boot(), which is intended to be invoked
783           at the end of the kernel-only boot sequence, just before
784           init is exec'ed.
786           Accept the default if unsure.
788 endmenu # "RCU Subsystem"
790 config BUILD_BIN2C
791         bool
792         default n
794 config IKCONFIG
795         tristate "Kernel .config support"
796         select BUILD_BIN2C
797         ---help---
798           This option enables the complete Linux kernel ".config" file
799           contents to be saved in the kernel. It provides documentation
800           of which kernel options are used in a running kernel or in an
801           on-disk kernel.  This information can be extracted from the kernel
802           image file with the script scripts/extract-ikconfig and used as
803           input to rebuild the current kernel or to build another kernel.
804           It can also be extracted from a running kernel by reading
805           /proc/config.gz if enabled (below).
807 config IKCONFIG_PROC
808         bool "Enable access to .config through /proc/config.gz"
809         depends on IKCONFIG && PROC_FS
810         ---help---
811           This option enables access to the kernel configuration file
812           through /proc/config.gz.
814 config LOG_BUF_SHIFT
815         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
816         range 12 25
817         default 17
818         depends on PRINTK
819         help
820           Select the minimal kernel log buffer size as a power of 2.
821           The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
822           parameter, see below. Any higher size also might be forced
823           by "log_buf_len" boot parameter.
825           Examples:
826                      17 => 128 KB
827                      16 => 64 KB
828                      15 => 32 KB
829                      14 => 16 KB
830                      13 =>  8 KB
831                      12 =>  4 KB
834         int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
835         depends on SMP
836         range 0 21
837         default 12 if !BASE_SMALL
838         default 0 if BASE_SMALL
839         depends on PRINTK
840         help
841           This option allows to increase the default ring buffer size
842           according to the number of CPUs. The value defines the contribution
843           of each CPU as a power of 2. The used space is typically only few
844           lines however it might be much more when problems are reported,
845           e.g. backtraces.
847           The increased size means that a new buffer has to be allocated and
848           the original static one is unused. It makes sense only on systems
849           with more CPUs. Therefore this value is used only when the sum of
850           contributions is greater than the half of the default kernel ring
851           buffer as defined by LOG_BUF_SHIFT. The default values are set
852           so that more than 64 CPUs are needed to trigger the allocation.
854           Also this option is ignored when "log_buf_len" kernel parameter is
855           used as it forces an exact (power of two) size of the ring buffer.
857           The number of possible CPUs is used for this computation ignoring
858           hotplugging making the compuation optimal for the the worst case
859           scenerio while allowing a simple algorithm to be used from bootup.
861           Examples shift values and their meaning:
862                      17 => 128 KB for each CPU
863                      16 =>  64 KB for each CPU
864                      15 =>  32 KB for each CPU
865                      14 =>  16 KB for each CPU
866                      13 =>   8 KB for each CPU
867                      12 =>   4 KB for each CPU
869 #
870 # Architectures with an unreliable sched_clock() should select this:
871 #
873         bool
876         bool
878 #
879 # For architectures that want to enable the support for NUMA-affine scheduler
880 # balancing logic:
881 #
883         bool
885 #
886 # For architectures that prefer to flush all TLBs after a number of pages
887 # are unmapped instead of sending one IPI per page to flush. The architecture
888 # must provide guarantees on what happens if a clean TLB cache entry is
889 # written after the unmap. Details are in mm/rmap.c near the check for
890 # should_defer_flush. The architecture should also consider if the full flush
891 # and the refill costs are offset by the savings of sending fewer IPIs.
893         bool
895 #
896 # For architectures that know their GCC __int128 support is sound
897 #
898 config ARCH_SUPPORTS_INT128
899         bool
901 # For architectures that (ab)use NUMA to represent different memory regions
902 # all cpu-local but of different latencies, such as SuperH.
903 #
905         bool
908         bool "Memory placement aware NUMA scheduler"
909         depends on ARCH_SUPPORTS_NUMA_BALANCING
910         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
911         depends on SMP && NUMA && MIGRATION
912         help
913           This option adds support for automatic NUMA aware memory/task placement.
914           The mechanism is quite primitive and is based on migrating memory when
915           it has references to the node the task is running on.
917           This system will be inactive on UMA systems.
920         bool "Automatically enable NUMA aware memory/task placement"
921         default y
922         depends on NUMA_BALANCING
923         help
924           If set, automatic NUMA balancing will be enabled if running on a NUMA
925           machine.
927 menuconfig CGROUPS
928         bool "Control Group support"
929         select KERNFS
930         help
931           This option adds support for grouping sets of processes together, for
932           use with process control subsystems such as Cpusets, CFS, memory
933           controls or device isolation.
934           See
935                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
936                 - Documentation/cgroups/ (features for grouping, isolation
937                                           and resource control)
939           Say N if unsure.
941 if CGROUPS
943 config CGROUP_DEBUG
944         bool "Example debug cgroup subsystem"
945         default n
946         help
947           This option enables a simple cgroup subsystem that
948           exports useful debugging information about the cgroups
949           framework.
951           Say N if unsure.
954         bool "Freezer cgroup subsystem"
955         help
956           Provides a way to freeze and unfreeze all tasks in a
957           cgroup.
959 config CGROUP_PIDS
960         bool "PIDs cgroup subsystem"
961         help
962           Provides enforcement of process number limits in the scope of a
963           cgroup. Any attempt to fork more processes than is allowed in the
964           cgroup will fail. PIDs are fundamentally a global resource because it
965           is fairly trivial to reach PID exhaustion before you reach even a
966           conservative kmemcg limit. As a result, it is possible to grind a
967           system to halt without being limited by other cgroup policies. The
968           PIDs cgroup subsystem is designed to stop this from happening.
970           It should be noted that organisational operations (such as attaching
971           to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
972           since the PIDs limit only affects a process's ability to fork, not to
973           attach to a cgroup.
975 config CGROUP_DEVICE
976         bool "Device controller for cgroups"
977         help
978           Provides a cgroup implementing whitelists for devices which
979           a process in the cgroup can mknod or open.
981 config CPUSETS
982         bool "Cpuset support"
983         help
984           This option will let you create and manage CPUSETs which
985           allow dynamically partitioning a system into sets of CPUs and
986           Memory Nodes and assigning tasks to run only within those sets.
987           This is primarily useful on large SMP or NUMA systems.
989           Say N if unsure.
991 config PROC_PID_CPUSET
992         bool "Include legacy /proc/<pid>/cpuset file"
993         depends on CPUSETS
994         default y
997         bool "Simple CPU accounting cgroup subsystem"
998         help
999           Provides a simple Resource Controller for monitoring the
1000           total CPU consumed by the tasks in a cgroup.
1002 config PAGE_COUNTER
1003        bool
1005 config MEMCG
1006         bool "Memory Resource Controller for Control Groups"
1007         select PAGE_COUNTER
1008         select EVENTFD
1009         help
1010           Provides a memory resource controller that manages both anonymous
1011           memory and page cache. (See Documentation/cgroups/memory.txt)
1013 config MEMCG_SWAP
1014         bool "Memory Resource Controller Swap Extension"
1015         depends on MEMCG && SWAP
1016         help
1017           Add swap management feature to memory resource controller. When you
1018           enable this, you can limit mem+swap usage per cgroup. In other words,
1019           when you disable this, memory resource controller has no cares to
1020           usage of swap...a process can exhaust all of the swap. This extension
1021           is useful when you want to avoid exhaustion swap but this itself
1022           adds more overheads and consumes memory for remembering information.
1023           Especially if you use 32bit system or small memory system, please
1024           be careful about enabling this. When memory resource controller
1025           is disabled by boot option, this will be automatically disabled and
1026           there will be no overhead from this. Even when you set this config=y,
1027           if boot option "swapaccount=0" is set, swap will not be accounted.
1028           Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1029           size is 4096bytes, 512k per 1Gbytes of swap.
1031         bool "Memory Resource Controller Swap Extension enabled by default"
1032         depends on MEMCG_SWAP
1033         default y
1034         help
1035           Memory Resource Controller Swap Extension comes with its price in
1036           a bigger memory consumption. General purpose distribution kernels
1037           which want to enable the feature but keep it disabled by default
1038           and let the user enable it by swapaccount=1 boot command line
1039           parameter should have this option unselected.
1040           For those who want to have the feature enabled by default should
1041           select this option (if, for some reason, they need to disable it
1042           then swapaccount=0 does the trick).
1043 config MEMCG_KMEM
1044         bool "Memory Resource Controller Kernel Memory accounting"
1045         depends on MEMCG
1046         depends on SLUB || SLAB
1047         help
1048           The Kernel Memory extension for Memory Resource Controller can limit
1049           the amount of memory used by kernel objects in the system. Those are
1050           fundamentally different from the entities handled by the standard
1051           Memory Controller, which are page-based, and can be swapped. Users of
1052           the kmem extension can use it to guarantee that no group of processes
1053           will ever exhaust kernel resources alone.
1055 config CGROUP_HUGETLB
1056         bool "HugeTLB Resource Controller for Control Groups"
1057         depends on HUGETLB_PAGE
1058         select PAGE_COUNTER
1059         default n
1060         help
1061           Provides a cgroup Resource Controller for HugeTLB pages.
1062           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1063           The limit is enforced during page fault. Since HugeTLB doesn't
1064           support page reclaim, enforcing the limit at page fault time implies
1065           that, the application will get SIGBUS signal if it tries to access
1066           HugeTLB pages beyond its limit. This requires the application to know
1067           beforehand how much HugeTLB pages it would require for its use. The
1068           control group is tracked in the third page lru pointer. This means
1069           that we cannot use the controller with huge page less than 3 pages.
1071 config CGROUP_PERF
1072         bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1073         depends on PERF_EVENTS && CGROUPS
1074         help
1075           This option extends the per-cpu mode to restrict monitoring to
1076           threads which belong to the cgroup specified and run on the
1077           designated cpu.
1079           Say N if unsure.
1081 menuconfig CGROUP_SCHED
1082         bool "Group CPU scheduler"
1083         default n
1084         help
1085           This feature lets CPU scheduler recognize task groups and control CPU
1086           bandwidth allocation to such task groups. It uses cgroups to group
1087           tasks.
1090 config FAIR_GROUP_SCHED
1091         bool "Group scheduling for SCHED_OTHER"
1092         depends on CGROUP_SCHED
1093         default CGROUP_SCHED
1095 config CFS_BANDWIDTH
1096         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1097         depends on FAIR_GROUP_SCHED
1098         default n
1099         help
1100           This option allows users to define CPU bandwidth rates (limits) for
1101           tasks running within the fair group scheduler.  Groups with no limit
1102           set are considered to be unconstrained and will run with no
1103           restriction.
1104           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1106 config RT_GROUP_SCHED
1107         bool "Group scheduling for SCHED_RR/FIFO"
1108         depends on CGROUP_SCHED
1109         default n
1110         help
1111           This feature lets you explicitly allocate real CPU bandwidth
1112           to task groups. If enabled, it will also make it impossible to
1113           schedule realtime tasks for non-root users until you allocate
1114           realtime bandwidth for them.
1115           See Documentation/scheduler/sched-rt-group.txt for more information.
1117 endif #CGROUP_SCHED
1119 config BLK_CGROUP
1120         bool "Block IO controller"
1121         depends on BLOCK
1122         default n
1123         ---help---
1124         Generic block IO controller cgroup interface. This is the common
1125         cgroup interface which should be used by various IO controlling
1126         policies.
1128         Currently, CFQ IO scheduler uses it to recognize task groups and
1129         control disk bandwidth allocation (proportional time slice allocation)
1130         to such task groups. It is also used by bio throttling logic in
1131         block layer to implement upper limit in IO rates on a device.
1133         This option only enables generic Block IO controller infrastructure.
1134         One needs to also enable actual IO controlling logic/policy. For
1135         enabling proportional weight division of disk bandwidth in CFQ, set
1136         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1139         See Documentation/cgroups/blkio-controller.txt for more information.
1141 config DEBUG_BLK_CGROUP
1142         bool "Enable Block IO controller debugging"
1143         depends on BLK_CGROUP
1144         default n
1145         ---help---
1146         Enable some debugging help. Currently it exports additional stat
1147         files in a cgroup which can be useful for debugging.
1150         bool
1151         depends on MEMCG && BLK_CGROUP
1152         default y
1154 endif # CGROUPS
1157         bool "Checkpoint/restore support" if EXPERT
1158         select PROC_CHILDREN
1159         default n
1160         help
1161           Enables additional kernel features in a sake of checkpoint/restore.
1162           In particular it adds auxiliary prctl codes to setup process text,
1163           data and heap segment sizes, and a few additional /proc filesystem
1164           entries.
1166           If unsure, say N here.
1168 menuconfig NAMESPACES
1169         bool "Namespaces support" if EXPERT
1170         depends on MULTIUSER
1171         default !EXPERT
1172         help
1173           Provides the way to make tasks work with different objects using
1174           the same id. For example same IPC id may refer to different objects
1175           or same user id or pid may refer to different tasks when used in
1176           different namespaces.
1180 config UTS_NS
1181         bool "UTS namespace"
1182         default y
1183         help
1184           In this namespace tasks see different info provided with the
1185           uname() system call
1187 config IPC_NS
1188         bool "IPC namespace"
1189         depends on (SYSVIPC || POSIX_MQUEUE)
1190         default y
1191         help
1192           In this namespace tasks work with IPC ids which correspond to
1193           different IPC objects in different namespaces.
1195 config USER_NS
1196         bool "User namespace"
1197         default n
1198         help
1199           This allows containers, i.e. vservers, to use user namespaces
1200           to provide different user info for different servers.
1202           When user namespaces are enabled in the kernel it is
1203           recommended that the MEMCG and MEMCG_KMEM options also be
1204           enabled and that user-space use the memory control groups to
1205           limit the amount of memory a memory unprivileged users can
1206           use.
1208           If unsure, say N.
1210 config PID_NS
1211         bool "PID Namespaces"
1212         default y
1213         help
1214           Support process id namespaces.  This allows having multiple
1215           processes with the same pid as long as they are in different
1216           pid namespaces.  This is a building block of containers.
1218 config NET_NS
1219         bool "Network namespace"
1220         depends on NET
1221         default y
1222         help
1223           Allow user space to create what appear to be multiple instances
1224           of the network stack.
1226 endif # NAMESPACES
1229         bool "Automatic process group scheduling"
1230         select CGROUPS
1231         select CGROUP_SCHED
1232         select FAIR_GROUP_SCHED
1233         help
1234           This option optimizes the scheduler for common desktop workloads by
1235           automatically creating and populating task groups.  This separation
1236           of workloads isolates aggressive CPU burners (like build jobs) from
1237           desktop applications.  Task group autogeneration is currently based
1238           upon task session.
1241         bool "Enable deprecated sysfs features to support old userspace tools"
1242         depends on SYSFS
1243         default n
1244         help
1245           This option adds code that switches the layout of the "block" class
1246           devices, to not show up in /sys/class/block/, but only in
1247           /sys/block/.
1249           This switch is only active when the sysfs.deprecated=1 boot option is
1250           passed or the SYSFS_DEPRECATED_V2 option is set.
1252           This option allows new kernels to run on old distributions and tools,
1253           which might get confused by /sys/class/block/. Since 2007/2008 all
1254           major distributions and tools handle this just fine.
1256           Recent distributions and userspace tools after 2009/2010 depend on
1257           the existence of /sys/class/block/, and will not work with this
1258           option enabled.
1260           Only if you are using a new kernel on an old distribution, you might
1261           need to say Y here.
1264         bool "Enable deprecated sysfs features by default"
1265         default n
1266         depends on SYSFS
1267         depends on SYSFS_DEPRECATED
1268         help
1269           Enable deprecated sysfs by default.
1271           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1272           option.
1274           Only if you are using a new kernel on an old distribution, you might
1275           need to say Y here. Even then, odds are you would not need it
1276           enabled, you can always pass the boot option if absolutely necessary.
1278 config RELAY
1279         bool "Kernel->user space relay support (formerly relayfs)"
1280         help
1281           This option enables support for relay interface support in
1282           certain file systems (such as debugfs).
1283           It is designed to provide an efficient mechanism for tools and
1284           facilities to relay large amounts of data from kernel space to
1285           user space.
1287           If unsure, say N.
1289 config BLK_DEV_INITRD
1290         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1291         depends on BROKEN || !FRV
1292         help
1293           The initial RAM filesystem is a ramfs which is loaded by the
1294           boot loader (loadlin or lilo) and that is mounted as root
1295           before the normal boot procedure. It is typically used to
1296           load modules needed to mount the "real" root file system,
1297           etc. See <file:Documentation/initrd.txt> for details.
1299           If RAM disk support (BLK_DEV_RAM) is also included, this
1300           also enables initial RAM disk (initrd) support and adds
1301           15 Kbytes (more on some other architectures) to the kernel size.
1303           If unsure say Y.
1307 source "usr/Kconfig"
1309 endif
1312         bool "Optimize for size"
1313         help
1314           Enabling this option will pass "-Os" instead of "-O2" to
1315           your compiler resulting in a smaller kernel.
1317           If unsure, say N.
1319 config SYSCTL
1320         bool
1322 config ANON_INODES
1323         bool
1325 config HAVE_UID16
1326         bool
1329         bool
1330         help
1331           Enable support for /proc/sys/debug/exception-trace.
1334         bool
1335         help
1336           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1337           Allows arch to define/use @no_unaligned_warning to possibly warn
1338           about unaligned access emulation going on under the hood.
1341         bool
1342         help
1343           Enable support for /proc/sys/kernel/unaligned-trap
1344           Allows arches to define/use @unaligned_enabled to runtime toggle
1345           the unaligned access emulation.
1346           see arch/parisc/kernel/unaligned.c for reference
1349         bool
1351 # interpreter that classic socket filters depend on
1352 config BPF
1353         bool
1355 menuconfig EXPERT
1356         bool "Configure standard kernel features (expert users)"
1357         # Unhide debug options, to make the on-by-default options visible
1358         select DEBUG_KERNEL
1359         help
1360           This option allows certain base kernel options and settings
1361           to be disabled or tweaked. This is for specialized
1362           environments which can tolerate a "non-standard" kernel.
1363           Only use this if you really know what you are doing.
1365 config UID16
1366         bool "Enable 16-bit UID system calls" if EXPERT
1367         depends on HAVE_UID16 && MULTIUSER
1368         default y
1369         help
1370           This enables the legacy 16-bit UID syscall wrappers.
1372 config MULTIUSER
1373         bool "Multiple users, groups and capabilities support" if EXPERT
1374         default y
1375         help
1376           This option enables support for non-root users, groups and
1377           capabilities.
1379           If you say N here, all processes will run with UID 0, GID 0, and all
1380           possible capabilities.  Saying N here also compiles out support for
1381           system calls related to UIDs, GIDs, and capabilities, such as setuid,
1382           setgid, and capset.
1384           If unsure, say Y here.
1387         bool "sgetmask/ssetmask syscalls support" if EXPERT
1388         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1389         ---help---
1390           sys_sgetmask and sys_ssetmask are obsolete system calls
1391           no longer supported in libc but still enabled by default in some
1392           architectures.
1394           If unsure, leave the default option here.
1396 config SYSFS_SYSCALL
1397         bool "Sysfs syscall support" if EXPERT
1398         default y
1399         ---help---
1400           sys_sysfs is an obsolete system call no longer supported in libc.
1401           Note that disabling this option is more secure but might break
1402           compatibility with some systems.
1404           If unsure say Y here.
1406 config SYSCTL_SYSCALL
1407         bool "Sysctl syscall support" if EXPERT
1408         depends on PROC_SYSCTL
1409         default n
1410         select SYSCTL
1411         ---help---
1412           sys_sysctl uses binary paths that have been found challenging
1413           to properly maintain and use.  The interface in /proc/sys
1414           using paths with ascii names is now the primary path to this
1415           information.
1417           Almost nothing using the binary sysctl interface so if you are
1418           trying to save some space it is probably safe to disable this,
1419           making your kernel marginally smaller.
1421           If unsure say N here.
1423 config KALLSYMS
1424          bool "Load all symbols for debugging/ksymoops" if EXPERT
1425          default y
1426          help
1427            Say Y here to let the kernel print out symbolic crash information and
1428            symbolic stack backtraces. This increases the size of the kernel
1429            somewhat, as all symbols have to be loaded into the kernel image.
1431 config KALLSYMS_ALL
1432         bool "Include all symbols in kallsyms"
1433         depends on DEBUG_KERNEL && KALLSYMS
1434         help
1435            Normally kallsyms only contains the symbols of functions for nicer
1436            OOPS messages and backtraces (i.e., symbols from the text and inittext
1437            sections). This is sufficient for most cases. And only in very rare
1438            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1439            names of variables from the data sections, etc).
1441            This option makes sure that all symbols are loaded into the kernel
1442            image (i.e., symbols from all sections) in cost of increased kernel
1443            size (depending on the kernel configuration, it may be 300KiB or
1444            something like this).
1446            Say N unless you really need all symbols.
1448 config PRINTK
1449         default y
1450         bool "Enable support for printk" if EXPERT
1451         select IRQ_WORK
1452         help
1453           This option enables normal printk support. Removing it
1454           eliminates most of the message strings from the kernel image
1455           and makes the kernel more or less silent. As this makes it
1456           very difficult to diagnose system problems, saying N here is
1457           strongly discouraged.
1459 config BUG
1460         bool "BUG() support" if EXPERT
1461         default y
1462         help
1463           Disabling this option eliminates support for BUG and WARN, reducing
1464           the size of your kernel image and potentially quietly ignoring
1465           numerous fatal conditions. You should only consider disabling this
1466           option for embedded systems with no facilities for reporting errors.
1467           Just say Y.
1469 config ELF_CORE
1470         depends on COREDUMP
1471         default y
1472         bool "Enable ELF core dumps" if EXPERT
1473         help
1474           Enable support for generating core dumps. Disabling saves about 4k.
1478         bool "Enable PC-Speaker support" if EXPERT
1479         depends on HAVE_PCSPKR_PLATFORM
1480         select I8253_LOCK
1481         default y
1482         help
1483           This option allows to disable the internal PC-Speaker
1484           support, saving some memory.
1486 config BASE_FULL
1487         default y
1488         bool "Enable full-sized data structures for core" if EXPERT
1489         help
1490           Disabling this option reduces the size of miscellaneous core
1491           kernel data structures. This saves memory on small machines,
1492           but may reduce performance.
1494 config FUTEX
1495         bool "Enable futex support" if EXPERT
1496         default y
1497         select RT_MUTEXES
1498         help
1499           Disabling this option will cause the kernel to be built without
1500           support for "fast userspace mutexes".  The resulting kernel may not
1501           run glibc-based applications correctly.
1504         bool
1505         depends on FUTEX
1506         help
1507           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1508           is implemented and always working. This removes a couple of runtime
1509           checks.
1511 config EPOLL
1512         bool "Enable eventpoll support" if EXPERT
1513         default y
1514         select ANON_INODES
1515         help
1516           Disabling this option will cause the kernel to be built without
1517           support for epoll family of system calls.
1519 config SIGNALFD
1520         bool "Enable signalfd() system call" if EXPERT
1521         select ANON_INODES
1522         default y
1523         help
1524           Enable the signalfd() system call that allows to receive signals
1525           on a file descriptor.
1527           If unsure, say Y.
1529 config TIMERFD
1530         bool "Enable timerfd() system call" if EXPERT
1531         select ANON_INODES
1532         default y
1533         help
1534           Enable the timerfd() system call that allows to receive timer
1535           events on a file descriptor.
1537           If unsure, say Y.
1539 config EVENTFD
1540         bool "Enable eventfd() system call" if EXPERT
1541         select ANON_INODES
1542         default y
1543         help
1544           Enable the eventfd() system call that allows to receive both
1545           kernel notification (ie. KAIO) or userspace notifications.
1547           If unsure, say Y.
1549 # syscall, maps, verifier
1550 config BPF_SYSCALL
1551         bool "Enable bpf() system call"
1552         select ANON_INODES
1553         select BPF
1554         default n
1555         help
1556           Enable the bpf() system call that allows to manipulate eBPF
1557           programs and maps via file descriptors.
1559 config SHMEM
1560         bool "Use full shmem filesystem" if EXPERT
1561         default y
1562         depends on MMU
1563         help
1564           The shmem is an internal filesystem used to manage shared memory.
1565           It is backed by swap and manages resource limits. It is also exported
1566           to userspace as tmpfs if TMPFS is enabled. Disabling this
1567           option replaces shmem and tmpfs with the much simpler ramfs code,
1568           which may be appropriate on small systems without swap.
1570 config AIO
1571         bool "Enable AIO support" if EXPERT
1572         default y
1573         help
1574           This option enables POSIX asynchronous I/O which may by used
1575           by some high performance threaded applications. Disabling
1576           this option saves about 7k.
1579         bool "Enable madvise/fadvise syscalls" if EXPERT
1580         default y
1581         help
1582           This option enables the madvise and fadvise syscalls, used by
1583           applications to advise the kernel about their future memory or file
1584           usage, improving performance. If building an embedded system where no
1585           applications use these syscalls, you can disable this option to save
1586           space.
1588 config USERFAULTFD
1589         bool "Enable userfaultfd() system call"
1590         select ANON_INODES
1591         depends on MMU
1592         help
1593           Enable the userfaultfd() system call that allows to intercept and
1594           handle page faults in userland.
1596 config PCI_QUIRKS
1597         default y
1598         bool "Enable PCI quirk workarounds" if EXPERT
1599         depends on PCI
1600         help
1601           This enables workarounds for various PCI chipset
1602           bugs/quirks. Disable this only if your target machine is
1603           unaffected by PCI quirks.
1605 config MEMBARRIER
1606         bool "Enable membarrier() system call" if EXPERT
1607         default y
1608         help
1609           Enable the membarrier() system call that allows issuing memory
1610           barriers across all running threads, which can be used to distribute
1611           the cost of user-space memory barriers asymmetrically by transforming
1612           pairs of memory barriers into pairs consisting of membarrier() and a
1613           compiler barrier.
1615           If unsure, say Y.
1617 config EMBEDDED
1618         bool "Embedded system"
1619         option allnoconfig_y
1620         select EXPERT
1621         help
1622           This option should be enabled if compiling the kernel for
1623           an embedded system so certain expert options are available
1624           for configuration.
1626 config HAVE_PERF_EVENTS
1627         bool
1628         help
1629           See tools/perf/design.txt for details.
1631 config PERF_USE_VMALLOC
1632         bool
1633         help
1634           See tools/perf/design.txt for details
1636 menu "Kernel Performance Events And Counters"
1638 config PERF_EVENTS
1639         bool "Kernel performance events and counters"
1640         default y if PROFILING
1641         depends on HAVE_PERF_EVENTS
1642         select ANON_INODES
1643         select IRQ_WORK
1644         select SRCU
1645         help
1646           Enable kernel support for various performance events provided
1647           by software and hardware.
1649           Software events are supported either built-in or via the
1650           use of generic tracepoints.
1652           Most modern CPUs support performance events via performance
1653           counter registers. These registers count the number of certain
1654           types of hw events: such as instructions executed, cachemisses
1655           suffered, or branches mis-predicted - without slowing down the
1656           kernel or applications. These registers can also trigger interrupts
1657           when a threshold number of events have passed - and can thus be
1658           used to profile the code that runs on that CPU.
1660           The Linux Performance Event subsystem provides an abstraction of
1661           these software and hardware event capabilities, available via a
1662           system call and used by the "perf" utility in tools/perf/. It
1663           provides per task and per CPU counters, and it provides event
1664           capabilities on top of those.
1666           Say Y if unsure.
1669         default n
1670         bool "Debug: use vmalloc to back perf mmap() buffers"
1671         depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1672         select PERF_USE_VMALLOC
1673         help
1674          Use vmalloc memory to back perf mmap() buffers.
1676          Mostly useful for debugging the vmalloc code on platforms
1677          that don't require it.
1679          Say N if unsure.
1681 endmenu
1684         default y
1685         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1686         help
1687           VM event counters are needed for event counts to be shown.
1688           This option allows the disabling of the VM event counters
1689           on EXPERT systems.  /proc/vmstat will only show page counts
1690           if VM event counters are disabled.
1692 config SLUB_DEBUG
1693         default y
1694         bool "Enable SLUB debugging support" if EXPERT
1695         depends on SLUB && SYSFS
1696         help
1697           SLUB has extensive debug support features. Disabling these can
1698           result in significant savings in code size. This also disables
1699           SLUB sysfs support. /sys/slab will not exist and there will be
1700           no support for cache validation etc.
1702 config COMPAT_BRK
1703         bool "Disable heap randomization"
1704         default y
1705         help
1706           Randomizing heap placement makes heap exploits harder, but it
1707           also breaks ancient binaries (including anything libc5 based).
1708           This option changes the bootup default to heap randomization
1709           disabled, and can be overridden at runtime by setting
1710           /proc/sys/kernel/randomize_va_space to 2.
1712           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1714 choice
1715         prompt "Choose SLAB allocator"
1716         default SLUB
1717         help
1718            This option allows to select a slab allocator.
1720 config SLAB
1721         bool "SLAB"
1722         help
1723           The regular slab allocator that is established and known to work
1724           well in all environments. It organizes cache hot objects in
1725           per cpu and per node queues.
1727 config SLUB
1728         bool "SLUB (Unqueued Allocator)"
1729         help
1730            SLUB is a slab allocator that minimizes cache line usage
1731            instead of managing queues of cached objects (SLAB approach).
1732            Per cpu caching is realized using slabs of objects instead
1733            of queues of objects. SLUB can use memory efficiently
1734            and has enhanced diagnostics. SLUB is the default choice for
1735            a slab allocator.
1737 config SLOB
1738         depends on EXPERT
1739         bool "SLOB (Simple Allocator)"
1740         help
1741            SLOB replaces the stock allocator with a drastically simpler
1742            allocator. SLOB is generally more space efficient but
1743            does not perform as well on large systems.
1745 endchoice
1747 config SLUB_CPU_PARTIAL
1748         default y
1749         depends on SLUB && SMP
1750         bool "SLUB per cpu partial cache"
1751         help
1752           Per cpu partial caches accellerate objects allocation and freeing
1753           that is local to a processor at the price of more indeterminism
1754           in the latency of the free. On overflow these caches will be cleared
1755           which requires the taking of locks that may cause latency spikes.
1756           Typically one would choose no for a realtime system.
1759         bool "Allow mmapped anonymous memory to be uninitialized"
1760         depends on EXPERT && !MMU
1761         default n
1762         help
1763           Normally, and according to the Linux spec, anonymous memory obtained
1764           from mmap() has it's contents cleared before it is passed to
1765           userspace.  Enabling this config option allows you to request that
1766           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1767           providing a huge performance boost.  If this option is not enabled,
1768           then the flag will be ignored.
1770           This is taken advantage of by uClibc's malloc(), and also by
1771           ELF-FDPIC binfmt's brk and stack allocator.
1773           Because of the obvious security issues, this option should only be
1774           enabled on embedded devices where you control what is run in
1775           userspace.  Since that isn't generally a problem on no-MMU systems,
1776           it is normally safe to say Y here.
1778           See Documentation/nommu-mmap.txt for more information.
1781         def_bool n
1782         select SYSTEM_TRUSTED_KEYRING
1783         select KEYS
1784         select CRYPTO
1785         select ASYMMETRIC_KEY_TYPE
1787         select PUBLIC_KEY_ALGO_RSA
1788         select ASN1
1789         select OID_REGISTRY
1790         select X509_CERTIFICATE_PARSER
1791         select PKCS7_MESSAGE_PARSER
1792         help
1793           Provide PKCS#7 message verification using the contents of the system
1794           trusted keyring to provide public keys.  This then can be used for
1795           module verification, kexec image verification and firmware blob
1796           verification.
1798 config PROFILING
1799         bool "Profiling support"
1800         help
1801           Say Y here to enable the extended profiling support mechanisms used
1802           by profilers such as OProfile.
1804 #
1805 # Place an empty function call at each tracepoint site. Can be
1806 # dynamically changed for a probe function.
1807 #
1808 config TRACEPOINTS
1809         bool
1811 source "arch/Kconfig"
1813 endmenu         # General setup
1816         bool
1817         default n
1819 config SLABINFO
1820         bool
1821         depends on PROC_FS
1822         depends on SLAB || SLUB_DEBUG
1823         default y
1825 config RT_MUTEXES
1826         bool
1828 config BASE_SMALL
1829         int
1830         default 0 if BASE_FULL
1831         default 1 if !BASE_FULL
1833 menuconfig MODULES
1834         bool "Enable loadable module support"
1835         option modules
1836         help
1837           Kernel modules are small pieces of compiled code which can
1838           be inserted in the running kernel, rather than being
1839           permanently built into the kernel.  You use the "modprobe"
1840           tool to add (and sometimes remove) them.  If you say Y here,
1841           many parts of the kernel can be built as modules (by
1842           answering M instead of Y where indicated): this is most
1843           useful for infrequently used options which are not required
1844           for booting.  For more information, see the man pages for
1845           modprobe, lsmod, modinfo, insmod and rmmod.
1847           If you say Y here, you will need to run "make
1848           modules_install" to put the modules under /lib/modules/
1849           where modprobe can find them (you may need to be root to do
1850           this).
1852           If unsure, say Y.
1854 if MODULES
1857         bool "Forced module loading"
1858         default n
1859         help
1860           Allow loading of modules without version information (ie. modprobe
1861           --force).  Forced module loading sets the 'F' (forced) taint flag and
1862           is usually a really bad idea.
1864 config MODULE_UNLOAD
1865         bool "Module unloading"
1866         help
1867           Without this option you will not be able to unload any
1868           modules (note that some modules may not be unloadable
1869           anyway), which makes your kernel smaller, faster
1870           and simpler.  If unsure, say Y.
1873         bool "Forced module unloading"
1874         depends on MODULE_UNLOAD
1875         help
1876           This option allows you to force a module to unload, even if the
1877           kernel believes it is unsafe: the kernel will remove the module
1878           without waiting for anyone to stop using it (using the -f option to
1879           rmmod).  This is mainly for kernel developers and desperate users.
1880           If unsure, say N.
1882 config MODVERSIONS
1883         bool "Module versioning support"
1884         help
1885           Usually, you have to use modules compiled with your kernel.
1886           Saying Y here makes it sometimes possible to use modules
1887           compiled for different kernels, by adding enough information
1888           to the modules to (hopefully) spot any changes which would
1889           make them incompatible with the kernel you are running.  If
1890           unsure, say N.
1893         bool "Source checksum for all modules"
1894         help
1895           Modules which contain a MODULE_VERSION get an extra "srcversion"
1896           field inserted into their modinfo section, which contains a
1897           sum of the source files which made it.  This helps maintainers
1898           see exactly which source was used to build a module (since
1899           others sometimes change the module source without updating
1900           the version).  With this option, such a "srcversion" field
1901           will be created for all modules.  If unsure, say N.
1903 config MODULE_SIG
1904         bool "Module signature verification"
1905         depends on MODULES
1906         select SYSTEM_DATA_VERIFICATION
1907         help
1908           Check modules for valid signatures upon load: the signature
1909           is simply appended to the module. For more information see
1910           Documentation/module-signing.txt.
1912           Note that this option adds the OpenSSL development packages as a
1913           kernel build dependency so that the signing tool can use its crypto
1914           library.
1916           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1917           module DOES NOT get stripped after being signed.  This includes the
1918           debuginfo strip done by some packagers (such as rpmbuild) and
1919           inclusion into an initramfs that wants the module size reduced.
1921 config MODULE_SIG_FORCE
1922         bool "Require modules to be validly signed"
1923         depends on MODULE_SIG
1924         help
1925           Reject unsigned modules or signed modules for which we don't have a
1926           key.  Without this, such modules will simply taint the kernel.
1928 config MODULE_SIG_ALL
1929         bool "Automatically sign all modules"
1930         default y
1931         depends on MODULE_SIG
1932         help
1933           Sign all modules during make modules_install. Without this option,
1934           modules must be signed manually, using the scripts/sign-file tool.
1936 comment "Do not forget to sign required modules with scripts/sign-file"
1937         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1939 choice
1940         prompt "Which hash algorithm should modules be signed with?"
1941         depends on MODULE_SIG
1942         help
1943           This determines which sort of hashing algorithm will be used during
1944           signature generation.  This algorithm _must_ be built into the kernel
1945           directly so that signature verification can take place.  It is not
1946           possible to load a signed module containing the algorithm to check
1947           the signature on that module.
1949 config MODULE_SIG_SHA1
1950         bool "Sign modules with SHA-1"
1951         select CRYPTO_SHA1
1953 config MODULE_SIG_SHA224
1954         bool "Sign modules with SHA-224"
1955         select CRYPTO_SHA256
1957 config MODULE_SIG_SHA256
1958         bool "Sign modules with SHA-256"
1959         select CRYPTO_SHA256
1961 config MODULE_SIG_SHA384
1962         bool "Sign modules with SHA-384"
1963         select CRYPTO_SHA512
1965 config MODULE_SIG_SHA512
1966         bool "Sign modules with SHA-512"
1967         select CRYPTO_SHA512
1969 endchoice
1971 config MODULE_SIG_HASH
1972         string
1973         depends on MODULE_SIG
1974         default "sha1" if MODULE_SIG_SHA1
1975         default "sha224" if MODULE_SIG_SHA224
1976         default "sha256" if MODULE_SIG_SHA256
1977         default "sha384" if MODULE_SIG_SHA384
1978         default "sha512" if MODULE_SIG_SHA512
1981         bool "Compress modules on installation"
1982         depends on MODULES
1983         help
1985           Compresses kernel modules when 'make modules_install' is run; gzip or
1986           xz depending on "Compression algorithm" below.
1988           module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
1990           Out-of-tree kernel modules installed using Kbuild will also be
1991           compressed upon installation.
1993           Note: for modules inside an initrd or initramfs, it's more efficient
1994           to compress the whole initrd or initramfs instead.
1996           Note: This is fully compatible with signed modules.
1998           If in doubt, say N.
2000 choice
2001         prompt "Compression algorithm"
2002         depends on MODULE_COMPRESS
2003         default MODULE_COMPRESS_GZIP
2004         help
2005           This determines which sort of compression will be used during
2006           'make modules_install'.
2008           GZIP (default) and XZ are supported.
2011         bool "GZIP"
2014         bool "XZ"
2016 endchoice
2018 endif # MODULES
2021         def_bool y
2022         depends on PERF_EVENTS || TRACING
2025         bool
2026         help
2027           Back when each arch used to define their own cpu_online_mask and
2028           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2029           with all 1s, and others with all 0s.  When they were centralised,
2030           it was better to provide this option than to break all the archs
2031           and have several arch maintainers pursuing me down dark alleys.
2033 source "block/Kconfig"
2036         bool
2038 config PADATA
2039         depends on SMP
2040         bool
2042 # Can be selected by architectures with broken toolchains
2043 # that get confused by correct const<->read_only section
2044 # mappings
2045 config BROKEN_RODATA
2046         bool
2048 config ASN1
2049         tristate
2050         help
2051           Build a simple ASN.1 grammar compiler that produces a bytecode output
2052           that can be interpreted by the ASN.1 stream decoder and used to
2053           inform it as to what tags are to be expected in a stream and what
2054           functions to call on what tags.
2056 source "kernel/Kconfig.locks"

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