Version:  2.0.40 2.2.26 2.4.37 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16

Linux/init/Kconfig

  1 config ARCH
  2         string
  3         option env="ARCH"
  4 
  5 config KERNELVERSION
  6         string
  7         option env="KERNELVERSION"
  8 
  9 config DEFCONFIG_LIST
 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"
 18 
 19 config CONSTRUCTORS
 20         bool
 21         depends on !UML
 22 
 23 config IRQ_WORK
 24         bool
 25 
 26 config BUILDTIME_EXTABLE_SORT
 27         bool
 28 
 29 menu "General setup"
 30 
 31 config BROKEN
 32         bool
 33 
 34 config BROKEN_ON_SMP
 35         bool
 36         depends on BROKEN || !SMP
 37         default y
 38 
 39 config INIT_ENV_ARG_LIMIT
 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.
 46 
 47 
 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.
 55 
 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.
 65 
 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.
 69 
 70 config LOCALVERSION
 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.
 79 
 80 config LOCALVERSION_AUTO
 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.
 87 
 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.
 92 
 93           (The actual string used here is the first eight characters produced
 94           by running the command:
 95 
 96             $ git rev-parse --verify HEAD
 97 
 98           which is done within the script "scripts/setlocalversion".)
 99 
100 config HAVE_KERNEL_GZIP
101         bool
102 
103 config HAVE_KERNEL_BZIP2
104         bool
105 
106 config HAVE_KERNEL_LZMA
107         bool
108 
109 config HAVE_KERNEL_XZ
110         bool
111 
112 config HAVE_KERNEL_LZO
113         bool
114 
115 config HAVE_KERNEL_LZ4
116         bool
117 
118 choice
119         prompt "Kernel compression mode"
120         default KERNEL_GZIP
121         depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
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.
128 
129           If you have any problems with bzip2 or lzma compressed
130           kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
131           version of this functionality (bzip2 only), for 2.4, was
132           supplied by Christian Ludwig)
133 
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.
137 
138           If in doubt, select 'gzip'
139 
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.
146 
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.
156 
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.
164 
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.
175 
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.
179 
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.
187 
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           <https://code.google.com/p/lz4/>.
195 
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.
199 
200 endchoice
201 
202 config DEFAULT_HOSTNAME
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.
210 
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.
220 
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 <http://www.tldp.org/docs.html#howto>),
230           you'll need to say Y here.
231 
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           <http://www.tldp.org/guides.html>.
235 
236 config SYSVIPC_SYSCTL
237         bool
238         depends on SYSVIPC
239         depends on SYSCTL
240         default y
241 
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.
251 
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.
255 
256           If unsure, say Y.
257 
258 config POSIX_MQUEUE_SYSCTL
259         bool
260         depends on POSIX_MQUEUE
261         depends on SYSCTL
262         default y
263 
264 config CROSS_MEMORY_ATTACH
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 to another process's address space.
272           See the man page for more details.
273 
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.
285 
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.
295 
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.
304 
305 config HAVE_ARCH_AUDITSYSCALL
306         bool
307 
308 config AUDITSYSCALL
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.
316 
317 config AUDIT_WATCH
318         def_bool y
319         depends on AUDITSYSCALL
320         select FSNOTIFY
321 
322 config AUDIT_TREE
323         def_bool y
324         depends on AUDITSYSCALL
325         select FSNOTIFY
326 
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
329 
330 menu "CPU/Task time and stats accounting"
331 
332 config VIRT_CPU_ACCOUNTING
333         bool
334 
335 choice
336         prompt "Cputime accounting"
337         default TICK_CPU_ACCOUNTING if !PPC64
338         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
339 
340 # Kind of a stub config for the pure tick based cputime accounting
341 config TICK_CPU_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.
348 
349           If unsure, say Y.
350 
351 config VIRT_CPU_ACCOUNTING_NATIVE
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.
363 
364 config VIRT_CPU_ACCOUNTING_GEN
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.
376 
377           For now this is only useful if you are working on the full
378           dynticks subsystem development.
379 
380           If unsure, say N.
381 
382 config IRQ_TIME_ACCOUNTING
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.
390 
391           If in doubt, say N here.
392 
393 endchoice
394 
395 config BSD_PROCESS_ACCT
396         bool "BSD Process Accounting"
397         help
398           If you say Y here, a user level program will be able to instruct the
399           kernel (via a special system call) to write process accounting
400           information to a file: whenever a process exits, information about
401           that process will be appended to the file by the kernel.  The
402           information includes things such as creation time, owning user,
403           command name, memory usage, controlling terminal etc. (the complete
404           list is in the struct acct in <file:include/linux/acct.h>).  It is
405           up to the user level program to do useful things with this
406           information.  This is generally a good idea, so say Y.
407 
408 config BSD_PROCESS_ACCT_V3
409         bool "BSD Process Accounting version 3 file format"
410         depends on BSD_PROCESS_ACCT
411         default n
412         help
413           If you say Y here, the process accounting information is written
414           in a new file format that also logs the process IDs of each
415           process and it's parent. Note that this file format is incompatible
416           with previous v0/v1/v2 file formats, so you will need updated tools
417           for processing it. A preliminary version of these tools is available
418           at <http://www.gnu.org/software/acct/>.
419 
420 config TASKSTATS
421         bool "Export task/process statistics through netlink"
422         depends on NET
423         default n
424         help
425           Export selected statistics for tasks/processes through the
426           generic netlink interface. Unlike BSD process accounting, the
427           statistics are available during the lifetime of tasks/processes as
428           responses to commands. Like BSD accounting, they are sent to user
429           space on task exit.
430 
431           Say N if unsure.
432 
433 config TASK_DELAY_ACCT
434         bool "Enable per-task delay accounting"
435         depends on TASKSTATS
436         help
437           Collect information on time spent by a task waiting for system
438           resources like cpu, synchronous block I/O completion and swapping
439           in pages. Such statistics can help in setting a task's priorities
440           relative to other tasks for cpu, io, rss limits etc.
441 
442           Say N if unsure.
443 
444 config TASK_XACCT
445         bool "Enable extended accounting over taskstats"
446         depends on TASKSTATS
447         help
448           Collect extended task accounting data and send the data
449           to userland for processing over the taskstats interface.
450 
451           Say N if unsure.
452 
453 config TASK_IO_ACCOUNTING
454         bool "Enable per-task storage I/O accounting"
455         depends on TASK_XACCT
456         help
457           Collect information on the number of bytes of storage I/O which this
458           task has caused.
459 
460           Say N if unsure.
461 
462 endmenu # "CPU/Task time and stats accounting"
463 
464 menu "RCU Subsystem"
465 
466 choice
467         prompt "RCU Implementation"
468         default TREE_RCU
469 
470 config TREE_RCU
471         bool "Tree-based hierarchical RCU"
472         depends on !PREEMPT && SMP
473         select IRQ_WORK
474         help
475           This option selects the RCU implementation that is
476           designed for very large SMP system with hundreds or
477           thousands of CPUs.  It also scales down nicely to
478           smaller systems.
479 
480 config TREE_PREEMPT_RCU
481         bool "Preemptible tree-based hierarchical RCU"
482         depends on PREEMPT
483         select IRQ_WORK
484         help
485           This option selects the RCU implementation that is
486           designed for very large SMP systems with hundreds or
487           thousands of CPUs, but for which real-time response
488           is also required.  It also scales down nicely to
489           smaller systems.
490 
491           Select this option if you are unsure.
492 
493 config TINY_RCU
494         bool "UP-only small-memory-footprint RCU"
495         depends on !PREEMPT && !SMP
496         help
497           This option selects the RCU implementation that is
498           designed for UP systems from which real-time response
499           is not required.  This option greatly reduces the
500           memory footprint of RCU.
501 
502 endchoice
503 
504 config PREEMPT_RCU
505         def_bool TREE_PREEMPT_RCU
506         help
507           This option enables preemptible-RCU code that is common between
508           the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
509 
510 config RCU_STALL_COMMON
511         def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
512         help
513           This option enables RCU CPU stall code that is common between
514           the TINY and TREE variants of RCU.  The purpose is to allow
515           the tiny variants to disable RCU CPU stall warnings, while
516           making these warnings mandatory for the tree variants.
517 
518 config CONTEXT_TRACKING
519        bool
520 
521 config RCU_USER_QS
522         bool "Consider userspace as in RCU extended quiescent state"
523         depends on HAVE_CONTEXT_TRACKING && SMP
524         select CONTEXT_TRACKING
525         help
526           This option sets hooks on kernel / userspace boundaries and
527           puts RCU in extended quiescent state when the CPU runs in
528           userspace. It means that when a CPU runs in userspace, it is
529           excluded from the global RCU state machine and thus doesn't
530           try to keep the timer tick on for RCU.
531 
532           Unless you want to hack and help the development of the full
533           dynticks mode, you shouldn't enable this option.  It also
534           adds unnecessary overhead.
535 
536           If unsure say N
537 
538 config CONTEXT_TRACKING_FORCE
539         bool "Force context tracking"
540         depends on CONTEXT_TRACKING
541         default y if !NO_HZ_FULL
542         help
543           The major pre-requirement for full dynticks to work is to
544           support the context tracking subsystem. But there are also
545           other dependencies to provide in order to make the full
546           dynticks working.
547 
548           This option stands for testing when an arch implements the
549           context tracking backend but doesn't yet fullfill all the
550           requirements to make the full dynticks feature working.
551           Without the full dynticks, there is no way to test the support
552           for context tracking and the subsystems that rely on it: RCU
553           userspace extended quiescent state and tickless cputime
554           accounting. This option copes with the absence of the full
555           dynticks subsystem by forcing the context tracking on all
556           CPUs in the system.
557 
558           Say Y only if you're working on the development of an
559           architecture backend for the context tracking.
560 
561           Say N otherwise, this option brings an overhead that you
562           don't want in production.
563 
564 
565 config RCU_FANOUT
566         int "Tree-based hierarchical RCU fanout value"
567         range 2 64 if 64BIT
568         range 2 32 if !64BIT
569         depends on TREE_RCU || TREE_PREEMPT_RCU
570         default 64 if 64BIT
571         default 32 if !64BIT
572         help
573           This option controls the fanout of hierarchical implementations
574           of RCU, allowing RCU to work efficiently on machines with
575           large numbers of CPUs.  This value must be at least the fourth
576           root of NR_CPUS, which allows NR_CPUS to be insanely large.
577           The default value of RCU_FANOUT should be used for production
578           systems, but if you are stress-testing the RCU implementation
579           itself, small RCU_FANOUT values allow you to test large-system
580           code paths on small(er) systems.
581 
582           Select a specific number if testing RCU itself.
583           Take the default if unsure.
584 
585 config RCU_FANOUT_LEAF
586         int "Tree-based hierarchical RCU leaf-level fanout value"
587         range 2 RCU_FANOUT if 64BIT
588         range 2 RCU_FANOUT if !64BIT
589         depends on TREE_RCU || TREE_PREEMPT_RCU
590         default 16
591         help
592           This option controls the leaf-level fanout of hierarchical
593           implementations of RCU, and allows trading off cache misses
594           against lock contention.  Systems that synchronize their
595           scheduling-clock interrupts for energy-efficiency reasons will
596           want the default because the smaller leaf-level fanout keeps
597           lock contention levels acceptably low.  Very large systems
598           (hundreds or thousands of CPUs) will instead want to set this
599           value to the maximum value possible in order to reduce the
600           number of cache misses incurred during RCU's grace-period
601           initialization.  These systems tend to run CPU-bound, and thus
602           are not helped by synchronized interrupts, and thus tend to
603           skew them, which reduces lock contention enough that large
604           leaf-level fanouts work well.
605 
606           Select a specific number if testing RCU itself.
607 
608           Select the maximum permissible value for large systems.
609 
610           Take the default if unsure.
611 
612 config RCU_FANOUT_EXACT
613         bool "Disable tree-based hierarchical RCU auto-balancing"
614         depends on TREE_RCU || TREE_PREEMPT_RCU
615         default n
616         help
617           This option forces use of the exact RCU_FANOUT value specified,
618           regardless of imbalances in the hierarchy.  This is useful for
619           testing RCU itself, and might one day be useful on systems with
620           strong NUMA behavior.
621 
622           Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
623 
624           Say N if unsure.
625 
626 config RCU_FAST_NO_HZ
627         bool "Accelerate last non-dyntick-idle CPU's grace periods"
628         depends on NO_HZ_COMMON && SMP
629         default n
630         help
631           This option permits CPUs to enter dynticks-idle state even if
632           they have RCU callbacks queued, and prevents RCU from waking
633           these CPUs up more than roughly once every four jiffies (by
634           default, you can adjust this using the rcutree.rcu_idle_gp_delay
635           parameter), thus improving energy efficiency.  On the other
636           hand, this option increases the duration of RCU grace periods,
637           for example, slowing down synchronize_rcu().
638 
639           Say Y if energy efficiency is critically important, and you
640                 don't care about increased grace-period durations.
641 
642           Say N if you are unsure.
643 
644 config TREE_RCU_TRACE
645         def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
646         select DEBUG_FS
647         help
648           This option provides tracing for the TREE_RCU and
649           TREE_PREEMPT_RCU implementations, permitting Makefile to
650           trivially select kernel/rcutree_trace.c.
651 
652 config RCU_BOOST
653         bool "Enable RCU priority boosting"
654         depends on RT_MUTEXES && PREEMPT_RCU
655         default n
656         help
657           This option boosts the priority of preempted RCU readers that
658           block the current preemptible RCU grace period for too long.
659           This option also prevents heavy loads from blocking RCU
660           callback invocation for all flavors of RCU.
661 
662           Say Y here if you are working with real-time apps or heavy loads
663           Say N here if you are unsure.
664 
665 config RCU_BOOST_PRIO
666         int "Real-time priority to boost RCU readers to"
667         range 1 99
668         depends on RCU_BOOST
669         default 1
670         help
671           This option specifies the real-time priority to which long-term
672           preempted RCU readers are to be boosted.  If you are working
673           with a real-time application that has one or more CPU-bound
674           threads running at a real-time priority level, you should set
675           RCU_BOOST_PRIO to a priority higher then the highest-priority
676           real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
677           of 1 is appropriate in the common case, which is real-time
678           applications that do not have any CPU-bound threads.
679 
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_BOOST_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_BOOST_PRIO should be
689           set to priority 6 or higher.
690 
691           Specify the real-time priority, or take the default if unsure.
692 
693 config RCU_BOOST_DELAY
694         int "Milliseconds to delay boosting after RCU grace-period start"
695         range 0 3000
696         depends on RCU_BOOST
697         default 500
698         help
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.
703 
704           Accept the default if unsure.
705 
706 config RCU_NOCB_CPU
707         bool "Offload RCU callback processing from boot-selected CPUs"
708         depends on TREE_RCU || TREE_PREEMPT_RCU
709         default n
710         help
711           Use this option to reduce OS jitter for aggressive HPC or
712           real-time workloads.  It can also be used to offload RCU
713           callback invocation to energy-efficient CPUs in battery-powered
714           asymmetric multiprocessors.
715 
716           This option offloads callback invocation from the set of
717           CPUs specified at boot time by the rcu_nocbs parameter.
718           For each such CPU, a kthread ("rcuox/N") will be created to
719           invoke callbacks, where the "N" is the CPU being offloaded,
720           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
721           "s" for RCU-sched.  Nothing prevents this kthread from running
722           on the specified CPUs, but (1) the kthreads may be preempted
723           between each callback, and (2) affinity or cgroups can be used
724           to force the kthreads to run on whatever set of CPUs is desired.
725 
726           Say Y here if you want to help to debug reduced OS jitter.
727           Say N here if you are unsure.
728 
729 choice
730         prompt "Build-forced no-CBs CPUs"
731         default RCU_NOCB_CPU_NONE
732         help
733           This option allows no-CBs CPUs (whose RCU callbacks are invoked
734           from kthreads rather than from softirq context) to be specified
735           at build time.  Additional no-CBs CPUs may be specified by
736           the rcu_nocbs= boot parameter.
737 
738 config RCU_NOCB_CPU_NONE
739         bool "No build_forced no-CBs CPUs"
740         depends on RCU_NOCB_CPU && !NO_HZ_FULL
741         help
742           This option does not force any of the CPUs to be no-CBs CPUs.
743           Only CPUs designated by the rcu_nocbs= boot parameter will be
744           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
745           kthreads whose names begin with "rcuo".  All other CPUs will
746           invoke their own RCU callbacks in softirq context.
747 
748           Select this option if you want to choose no-CBs CPUs at
749           boot time, for example, to allow testing of different no-CBs
750           configurations without having to rebuild the kernel each time.
751 
752 config RCU_NOCB_CPU_ZERO
753         bool "CPU 0 is a build_forced no-CBs CPU"
754         depends on RCU_NOCB_CPU && !NO_HZ_FULL
755         help
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
761           context.
762 
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.
766 
767 config RCU_NOCB_CPU_ALL
768         bool "All CPUs are build_forced no-CBs CPUs"
769         depends on RCU_NOCB_CPU
770         help
771           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
772           boot parameter will be ignored.  All CPUs' RCU callbacks will
773           be executed in the context of per-CPU rcuo kthreads created for
774           this purpose.  Assuming that the kthreads whose names start with
775           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
776           on the remaining CPUs, but might decrease memory locality during
777           RCU-callback invocation, thus potentially degrading throughput.
778 
779           Select this if all CPUs need to be no-CBs CPUs for real-time
780           or energy-efficiency reasons.
781 
782 endchoice
783 
784 endmenu # "RCU Subsystem"
785 
786 config IKCONFIG
787         tristate "Kernel .config support"
788         ---help---
789           This option enables the complete Linux kernel ".config" file
790           contents to be saved in the kernel. It provides documentation
791           of which kernel options are used in a running kernel or in an
792           on-disk kernel.  This information can be extracted from the kernel
793           image file with the script scripts/extract-ikconfig and used as
794           input to rebuild the current kernel or to build another kernel.
795           It can also be extracted from a running kernel by reading
796           /proc/config.gz if enabled (below).
797 
798 config IKCONFIG_PROC
799         bool "Enable access to .config through /proc/config.gz"
800         depends on IKCONFIG && PROC_FS
801         ---help---
802           This option enables access to the kernel configuration file
803           through /proc/config.gz.
804 
805 config LOG_BUF_SHIFT
806         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
807         range 12 21
808         default 17
809         help
810           Select kernel log buffer size as a power of 2.
811           Examples:
812                      17 => 128 KB
813                      16 => 64 KB
814                      15 => 32 KB
815                      14 => 16 KB
816                      13 =>  8 KB
817                      12 =>  4 KB
818 
819 #
820 # Architectures with an unreliable sched_clock() should select this:
821 #
822 config HAVE_UNSTABLE_SCHED_CLOCK
823         bool
824 
825 config GENERIC_SCHED_CLOCK
826         bool
827 
828 #
829 # For architectures that want to enable the support for NUMA-affine scheduler
830 # balancing logic:
831 #
832 config ARCH_SUPPORTS_NUMA_BALANCING
833         bool
834 
835 #
836 # For architectures that know their GCC __int128 support is sound
837 #
838 config ARCH_SUPPORTS_INT128
839         bool
840 
841 # For architectures that (ab)use NUMA to represent different memory regions
842 # all cpu-local but of different latencies, such as SuperH.
843 #
844 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
845         bool
846 
847 #
848 # For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
849 config ARCH_WANTS_PROT_NUMA_PROT_NONE
850         bool
851 
852 config ARCH_USES_NUMA_PROT_NONE
853         bool
854         default y
855         depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
856         depends on NUMA_BALANCING
857 
858 config NUMA_BALANCING_DEFAULT_ENABLED
859         bool "Automatically enable NUMA aware memory/task placement"
860         default y
861         depends on NUMA_BALANCING
862         help
863           If set, automatic NUMA balancing will be enabled if running on a NUMA
864           machine.
865 
866 config NUMA_BALANCING
867         bool "Memory placement aware NUMA scheduler"
868         depends on ARCH_SUPPORTS_NUMA_BALANCING
869         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
870         depends on SMP && NUMA && MIGRATION
871         help
872           This option adds support for automatic NUMA aware memory/task placement.
873           The mechanism is quite primitive and is based on migrating memory when
874           it has references to the node the task is running on.
875 
876           This system will be inactive on UMA systems.
877 
878 menuconfig CGROUPS
879         boolean "Control Group support"
880         select KERNFS
881         help
882           This option adds support for grouping sets of processes together, for
883           use with process control subsystems such as Cpusets, CFS, memory
884           controls or device isolation.
885           See
886                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
887                 - Documentation/cgroups/ (features for grouping, isolation
888                                           and resource control)
889 
890           Say N if unsure.
891 
892 if CGROUPS
893 
894 config CGROUP_DEBUG
895         bool "Example debug cgroup subsystem"
896         default n
897         help
898           This option enables a simple cgroup subsystem that
899           exports useful debugging information about the cgroups
900           framework.
901 
902           Say N if unsure.
903 
904 config CGROUP_FREEZER
905         bool "Freezer cgroup subsystem"
906         help
907           Provides a way to freeze and unfreeze all tasks in a
908           cgroup.
909 
910 config CGROUP_DEVICE
911         bool "Device controller for cgroups"
912         help
913           Provides a cgroup implementing whitelists for devices which
914           a process in the cgroup can mknod or open.
915 
916 config CPUSETS
917         bool "Cpuset support"
918         help
919           This option will let you create and manage CPUSETs which
920           allow dynamically partitioning a system into sets of CPUs and
921           Memory Nodes and assigning tasks to run only within those sets.
922           This is primarily useful on large SMP or NUMA systems.
923 
924           Say N if unsure.
925 
926 config PROC_PID_CPUSET
927         bool "Include legacy /proc/<pid>/cpuset file"
928         depends on CPUSETS
929         default y
930 
931 config CGROUP_CPUACCT
932         bool "Simple CPU accounting cgroup subsystem"
933         help
934           Provides a simple Resource Controller for monitoring the
935           total CPU consumed by the tasks in a cgroup.
936 
937 config RESOURCE_COUNTERS
938         bool "Resource counters"
939         help
940           This option enables controller independent resource accounting
941           infrastructure that works with cgroups.
942 
943 config MEMCG
944         bool "Memory Resource Controller for Control Groups"
945         depends on RESOURCE_COUNTERS
946         select EVENTFD
947         help
948           Provides a memory resource controller that manages both anonymous
949           memory and page cache. (See Documentation/cgroups/memory.txt)
950 
951           Note that setting this option increases fixed memory overhead
952           associated with each page of memory in the system. By this,
953           8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
954           usage tracking struct at boot. Total amount of this is printed out
955           at boot.
956 
957           Only enable when you're ok with these trade offs and really
958           sure you need the memory resource controller. Even when you enable
959           this, you can set "cgroup_disable=memory" at your boot option to
960           disable memory resource controller and you can avoid overheads.
961           (and lose benefits of memory resource controller)
962 
963 config MEMCG_SWAP
964         bool "Memory Resource Controller Swap Extension"
965         depends on MEMCG && SWAP
966         help
967           Add swap management feature to memory resource controller. When you
968           enable this, you can limit mem+swap usage per cgroup. In other words,
969           when you disable this, memory resource controller has no cares to
970           usage of swap...a process can exhaust all of the swap. This extension
971           is useful when you want to avoid exhaustion swap but this itself
972           adds more overheads and consumes memory for remembering information.
973           Especially if you use 32bit system or small memory system, please
974           be careful about enabling this. When memory resource controller
975           is disabled by boot option, this will be automatically disabled and
976           there will be no overhead from this. Even when you set this config=y,
977           if boot option "swapaccount=0" is set, swap will not be accounted.
978           Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
979           size is 4096bytes, 512k per 1Gbytes of swap.
980 config MEMCG_SWAP_ENABLED
981         bool "Memory Resource Controller Swap Extension enabled by default"
982         depends on MEMCG_SWAP
983         default y
984         help
985           Memory Resource Controller Swap Extension comes with its price in
986           a bigger memory consumption. General purpose distribution kernels
987           which want to enable the feature but keep it disabled by default
988           and let the user enable it by swapaccount=1 boot command line
989           parameter should have this option unselected.
990           For those who want to have the feature enabled by default should
991           select this option (if, for some reason, they need to disable it
992           then swapaccount=0 does the trick).
993 config MEMCG_KMEM
994         bool "Memory Resource Controller Kernel Memory accounting"
995         depends on MEMCG
996         depends on SLUB || SLAB
997         help
998           The Kernel Memory extension for Memory Resource Controller can limit
999           the amount of memory used by kernel objects in the system. Those are
1000           fundamentally different from the entities handled by the standard
1001           Memory Controller, which are page-based, and can be swapped. Users of
1002           the kmem extension can use it to guarantee that no group of processes
1003           will ever exhaust kernel resources alone.
1004 
1005           WARNING: Current implementation lacks reclaim support. That means
1006           allocation attempts will fail when close to the limit even if there
1007           are plenty of kmem available for reclaim. That makes this option
1008           unusable in real life so DO NOT SELECT IT unless for development
1009           purposes.
1010 
1011 config CGROUP_HUGETLB
1012         bool "HugeTLB Resource Controller for Control Groups"
1013         depends on RESOURCE_COUNTERS && HUGETLB_PAGE
1014         default n
1015         help
1016           Provides a cgroup Resource Controller for HugeTLB pages.
1017           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1018           The limit is enforced during page fault. Since HugeTLB doesn't
1019           support page reclaim, enforcing the limit at page fault time implies
1020           that, the application will get SIGBUS signal if it tries to access
1021           HugeTLB pages beyond its limit. This requires the application to know
1022           beforehand how much HugeTLB pages it would require for its use. The
1023           control group is tracked in the third page lru pointer. This means
1024           that we cannot use the controller with huge page less than 3 pages.
1025 
1026 config CGROUP_PERF
1027         bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1028         depends on PERF_EVENTS && CGROUPS
1029         help
1030           This option extends the per-cpu mode to restrict monitoring to
1031           threads which belong to the cgroup specified and run on the
1032           designated cpu.
1033 
1034           Say N if unsure.
1035 
1036 menuconfig CGROUP_SCHED
1037         bool "Group CPU scheduler"
1038         default n
1039         help
1040           This feature lets CPU scheduler recognize task groups and control CPU
1041           bandwidth allocation to such task groups. It uses cgroups to group
1042           tasks.
1043 
1044 if CGROUP_SCHED
1045 config FAIR_GROUP_SCHED
1046         bool "Group scheduling for SCHED_OTHER"
1047         depends on CGROUP_SCHED
1048         default CGROUP_SCHED
1049 
1050 config CFS_BANDWIDTH
1051         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1052         depends on FAIR_GROUP_SCHED
1053         default n
1054         help
1055           This option allows users to define CPU bandwidth rates (limits) for
1056           tasks running within the fair group scheduler.  Groups with no limit
1057           set are considered to be unconstrained and will run with no
1058           restriction.
1059           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1060 
1061 config RT_GROUP_SCHED
1062         bool "Group scheduling for SCHED_RR/FIFO"
1063         depends on CGROUP_SCHED
1064         default n
1065         help
1066           This feature lets you explicitly allocate real CPU bandwidth
1067           to task groups. If enabled, it will also make it impossible to
1068           schedule realtime tasks for non-root users until you allocate
1069           realtime bandwidth for them.
1070           See Documentation/scheduler/sched-rt-group.txt for more information.
1071 
1072 endif #CGROUP_SCHED
1073 
1074 config BLK_CGROUP
1075         bool "Block IO controller"
1076         depends on BLOCK
1077         default n
1078         ---help---
1079         Generic block IO controller cgroup interface. This is the common
1080         cgroup interface which should be used by various IO controlling
1081         policies.
1082 
1083         Currently, CFQ IO scheduler uses it to recognize task groups and
1084         control disk bandwidth allocation (proportional time slice allocation)
1085         to such task groups. It is also used by bio throttling logic in
1086         block layer to implement upper limit in IO rates on a device.
1087 
1088         This option only enables generic Block IO controller infrastructure.
1089         One needs to also enable actual IO controlling logic/policy. For
1090         enabling proportional weight division of disk bandwidth in CFQ, set
1091         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1092         CONFIG_BLK_DEV_THROTTLING=y.
1093 
1094         See Documentation/cgroups/blkio-controller.txt for more information.
1095 
1096 config DEBUG_BLK_CGROUP
1097         bool "Enable Block IO controller debugging"
1098         depends on BLK_CGROUP
1099         default n
1100         ---help---
1101         Enable some debugging help. Currently it exports additional stat
1102         files in a cgroup which can be useful for debugging.
1103 
1104 endif # CGROUPS
1105 
1106 config CHECKPOINT_RESTORE
1107         bool "Checkpoint/restore support" if EXPERT
1108         default n
1109         help
1110           Enables additional kernel features in a sake of checkpoint/restore.
1111           In particular it adds auxiliary prctl codes to setup process text,
1112           data and heap segment sizes, and a few additional /proc filesystem
1113           entries.
1114 
1115           If unsure, say N here.
1116 
1117 menuconfig NAMESPACES
1118         bool "Namespaces support" if EXPERT
1119         default !EXPERT
1120         help
1121           Provides the way to make tasks work with different objects using
1122           the same id. For example same IPC id may refer to different objects
1123           or same user id or pid may refer to different tasks when used in
1124           different namespaces.
1125 
1126 if NAMESPACES
1127 
1128 config UTS_NS
1129         bool "UTS namespace"
1130         default y
1131         help
1132           In this namespace tasks see different info provided with the
1133           uname() system call
1134 
1135 config IPC_NS
1136         bool "IPC namespace"
1137         depends on (SYSVIPC || POSIX_MQUEUE)
1138         default y
1139         help
1140           In this namespace tasks work with IPC ids which correspond to
1141           different IPC objects in different namespaces.
1142 
1143 config USER_NS
1144         bool "User namespace"
1145         default n
1146         help
1147           This allows containers, i.e. vservers, to use user namespaces
1148           to provide different user info for different servers.
1149 
1150           When user namespaces are enabled in the kernel it is
1151           recommended that the MEMCG and MEMCG_KMEM options also be
1152           enabled and that user-space use the memory control groups to
1153           limit the amount of memory a memory unprivileged users can
1154           use.
1155 
1156           If unsure, say N.
1157 
1158 config PID_NS
1159         bool "PID Namespaces"
1160         default y
1161         help
1162           Support process id namespaces.  This allows having multiple
1163           processes with the same pid as long as they are in different
1164           pid namespaces.  This is a building block of containers.
1165 
1166 config NET_NS
1167         bool "Network namespace"
1168         depends on NET
1169         default y
1170         help
1171           Allow user space to create what appear to be multiple instances
1172           of the network stack.
1173 
1174 endif # NAMESPACES
1175 
1176 config SCHED_AUTOGROUP
1177         bool "Automatic process group scheduling"
1178         select CGROUPS
1179         select CGROUP_SCHED
1180         select FAIR_GROUP_SCHED
1181         help
1182           This option optimizes the scheduler for common desktop workloads by
1183           automatically creating and populating task groups.  This separation
1184           of workloads isolates aggressive CPU burners (like build jobs) from
1185           desktop applications.  Task group autogeneration is currently based
1186           upon task session.
1187 
1188 config SYSFS_DEPRECATED
1189         bool "Enable deprecated sysfs features to support old userspace tools"
1190         depends on SYSFS
1191         default n
1192         help
1193           This option adds code that switches the layout of the "block" class
1194           devices, to not show up in /sys/class/block/, but only in
1195           /sys/block/.
1196 
1197           This switch is only active when the sysfs.deprecated=1 boot option is
1198           passed or the SYSFS_DEPRECATED_V2 option is set.
1199 
1200           This option allows new kernels to run on old distributions and tools,
1201           which might get confused by /sys/class/block/. Since 2007/2008 all
1202           major distributions and tools handle this just fine.
1203 
1204           Recent distributions and userspace tools after 2009/2010 depend on
1205           the existence of /sys/class/block/, and will not work with this
1206           option enabled.
1207 
1208           Only if you are using a new kernel on an old distribution, you might
1209           need to say Y here.
1210 
1211 config SYSFS_DEPRECATED_V2
1212         bool "Enable deprecated sysfs features by default"
1213         default n
1214         depends on SYSFS
1215         depends on SYSFS_DEPRECATED
1216         help
1217           Enable deprecated sysfs by default.
1218 
1219           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1220           option.
1221 
1222           Only if you are using a new kernel on an old distribution, you might
1223           need to say Y here. Even then, odds are you would not need it
1224           enabled, you can always pass the boot option if absolutely necessary.
1225 
1226 config RELAY
1227         bool "Kernel->user space relay support (formerly relayfs)"
1228         help
1229           This option enables support for relay interface support in
1230           certain file systems (such as debugfs).
1231           It is designed to provide an efficient mechanism for tools and
1232           facilities to relay large amounts of data from kernel space to
1233           user space.
1234 
1235           If unsure, say N.
1236 
1237 config BLK_DEV_INITRD
1238         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1239         depends on BROKEN || !FRV
1240         help
1241           The initial RAM filesystem is a ramfs which is loaded by the
1242           boot loader (loadlin or lilo) and that is mounted as root
1243           before the normal boot procedure. It is typically used to
1244           load modules needed to mount the "real" root file system,
1245           etc. See <file:Documentation/initrd.txt> for details.
1246 
1247           If RAM disk support (BLK_DEV_RAM) is also included, this
1248           also enables initial RAM disk (initrd) support and adds
1249           15 Kbytes (more on some other architectures) to the kernel size.
1250 
1251           If unsure say Y.
1252 
1253 if BLK_DEV_INITRD
1254 
1255 source "usr/Kconfig"
1256 
1257 endif
1258 
1259 config CC_OPTIMIZE_FOR_SIZE
1260         bool "Optimize for size"
1261         help
1262           Enabling this option will pass "-Os" instead of "-O2" to gcc
1263           resulting in a smaller kernel.
1264 
1265           If unsure, say N.
1266 
1267 config SYSCTL
1268         bool
1269 
1270 config ANON_INODES
1271         bool
1272 
1273 config HAVE_UID16
1274         bool
1275 
1276 config SYSCTL_EXCEPTION_TRACE
1277         bool
1278         help
1279           Enable support for /proc/sys/debug/exception-trace.
1280 
1281 config SYSCTL_ARCH_UNALIGN_NO_WARN
1282         bool
1283         help
1284           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1285           Allows arch to define/use @no_unaligned_warning to possibly warn
1286           about unaligned access emulation going on under the hood.
1287 
1288 config SYSCTL_ARCH_UNALIGN_ALLOW
1289         bool
1290         help
1291           Enable support for /proc/sys/kernel/unaligned-trap
1292           Allows arches to define/use @unaligned_enabled to runtime toggle
1293           the unaligned access emulation.
1294           see arch/parisc/kernel/unaligned.c for reference
1295 
1296 config HAVE_PCSPKR_PLATFORM
1297         bool
1298 
1299 menuconfig EXPERT
1300         bool "Configure standard kernel features (expert users)"
1301         # Unhide debug options, to make the on-by-default options visible
1302         select DEBUG_KERNEL
1303         help
1304           This option allows certain base kernel options and settings
1305           to be disabled or tweaked. This is for specialized
1306           environments which can tolerate a "non-standard" kernel.
1307           Only use this if you really know what you are doing.
1308 
1309 config UID16
1310         bool "Enable 16-bit UID system calls" if EXPERT
1311         depends on HAVE_UID16
1312         default y
1313         help
1314           This enables the legacy 16-bit UID syscall wrappers.
1315 
1316 config SGETMASK_SYSCALL
1317         bool "sgetmask/ssetmask syscalls support" if EXPERT
1318         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1319         ---help---
1320           sys_sgetmask and sys_ssetmask are obsolete system calls
1321           no longer supported in libc but still enabled by default in some
1322           architectures.
1323 
1324           If unsure, leave the default option here.
1325 
1326 config SYSFS_SYSCALL
1327         bool "Sysfs syscall support" if EXPERT
1328         default y
1329         ---help---
1330           sys_sysfs is an obsolete system call no longer supported in libc.
1331           Note that disabling this option is more secure but might break
1332           compatibility with some systems.
1333 
1334           If unsure say Y here.
1335 
1336 config SYSCTL_SYSCALL
1337         bool "Sysctl syscall support" if EXPERT
1338         depends on PROC_SYSCTL
1339         default n
1340         select SYSCTL
1341         ---help---
1342           sys_sysctl uses binary paths that have been found challenging
1343           to properly maintain and use.  The interface in /proc/sys
1344           using paths with ascii names is now the primary path to this
1345           information.
1346 
1347           Almost nothing using the binary sysctl interface so if you are
1348           trying to save some space it is probably safe to disable this,
1349           making your kernel marginally smaller.
1350 
1351           If unsure say N here.
1352 
1353 config KALLSYMS
1354          bool "Load all symbols for debugging/ksymoops" if EXPERT
1355          default y
1356          help
1357            Say Y here to let the kernel print out symbolic crash information and
1358            symbolic stack backtraces. This increases the size of the kernel
1359            somewhat, as all symbols have to be loaded into the kernel image.
1360 
1361 config KALLSYMS_ALL
1362         bool "Include all symbols in kallsyms"
1363         depends on DEBUG_KERNEL && KALLSYMS
1364         help
1365            Normally kallsyms only contains the symbols of functions for nicer
1366            OOPS messages and backtraces (i.e., symbols from the text and inittext
1367            sections). This is sufficient for most cases. And only in very rare
1368            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1369            names of variables from the data sections, etc).
1370 
1371            This option makes sure that all symbols are loaded into the kernel
1372            image (i.e., symbols from all sections) in cost of increased kernel
1373            size (depending on the kernel configuration, it may be 300KiB or
1374            something like this).
1375 
1376            Say N unless you really need all symbols.
1377 
1378 config PRINTK
1379         default y
1380         bool "Enable support for printk" if EXPERT
1381         select IRQ_WORK
1382         help
1383           This option enables normal printk support. Removing it
1384           eliminates most of the message strings from the kernel image
1385           and makes the kernel more or less silent. As this makes it
1386           very difficult to diagnose system problems, saying N here is
1387           strongly discouraged.
1388 
1389 config BUG
1390         bool "BUG() support" if EXPERT
1391         default y
1392         help
1393           Disabling this option eliminates support for BUG and WARN, reducing
1394           the size of your kernel image and potentially quietly ignoring
1395           numerous fatal conditions. You should only consider disabling this
1396           option for embedded systems with no facilities for reporting errors.
1397           Just say Y.
1398 
1399 config ELF_CORE
1400         depends on COREDUMP
1401         default y
1402         bool "Enable ELF core dumps" if EXPERT
1403         help
1404           Enable support for generating core dumps. Disabling saves about 4k.
1405 
1406 
1407 config PCSPKR_PLATFORM
1408         bool "Enable PC-Speaker support" if EXPERT
1409         depends on HAVE_PCSPKR_PLATFORM
1410         select I8253_LOCK
1411         default y
1412         help
1413           This option allows to disable the internal PC-Speaker
1414           support, saving some memory.
1415 
1416 config BASE_FULL
1417         default y
1418         bool "Enable full-sized data structures for core" if EXPERT
1419         help
1420           Disabling this option reduces the size of miscellaneous core
1421           kernel data structures. This saves memory on small machines,
1422           but may reduce performance.
1423 
1424 config FUTEX
1425         bool "Enable futex support" if EXPERT
1426         default y
1427         select RT_MUTEXES
1428         help
1429           Disabling this option will cause the kernel to be built without
1430           support for "fast userspace mutexes".  The resulting kernel may not
1431           run glibc-based applications correctly.
1432 
1433 config HAVE_FUTEX_CMPXCHG
1434         bool
1435         help
1436           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1437           is implemented and always working. This removes a couple of runtime
1438           checks.
1439 
1440 config EPOLL
1441         bool "Enable eventpoll support" if EXPERT
1442         default y
1443         select ANON_INODES
1444         help
1445           Disabling this option will cause the kernel to be built without
1446           support for epoll family of system calls.
1447 
1448 config SIGNALFD
1449         bool "Enable signalfd() system call" if EXPERT
1450         select ANON_INODES
1451         default y
1452         help
1453           Enable the signalfd() system call that allows to receive signals
1454           on a file descriptor.
1455 
1456           If unsure, say Y.
1457 
1458 config TIMERFD
1459         bool "Enable timerfd() system call" if EXPERT
1460         select ANON_INODES
1461         default y
1462         help
1463           Enable the timerfd() system call that allows to receive timer
1464           events on a file descriptor.
1465 
1466           If unsure, say Y.
1467 
1468 config EVENTFD
1469         bool "Enable eventfd() system call" if EXPERT
1470         select ANON_INODES
1471         default y
1472         help
1473           Enable the eventfd() system call that allows to receive both
1474           kernel notification (ie. KAIO) or userspace notifications.
1475 
1476           If unsure, say Y.
1477 
1478 config SHMEM
1479         bool "Use full shmem filesystem" if EXPERT
1480         default y
1481         depends on MMU
1482         help
1483           The shmem is an internal filesystem used to manage shared memory.
1484           It is backed by swap and manages resource limits. It is also exported
1485           to userspace as tmpfs if TMPFS is enabled. Disabling this
1486           option replaces shmem and tmpfs with the much simpler ramfs code,
1487           which may be appropriate on small systems without swap.
1488 
1489 config AIO
1490         bool "Enable AIO support" if EXPERT
1491         default y
1492         help
1493           This option enables POSIX asynchronous I/O which may by used
1494           by some high performance threaded applications. Disabling
1495           this option saves about 7k.
1496 
1497 config PCI_QUIRKS
1498         default y
1499         bool "Enable PCI quirk workarounds" if EXPERT
1500         depends on PCI
1501         help
1502           This enables workarounds for various PCI chipset
1503           bugs/quirks. Disable this only if your target machine is
1504           unaffected by PCI quirks.
1505 
1506 config EMBEDDED
1507         bool "Embedded system"
1508         option allnoconfig_y
1509         select EXPERT
1510         help
1511           This option should be enabled if compiling the kernel for
1512           an embedded system so certain expert options are available
1513           for configuration.
1514 
1515 config HAVE_PERF_EVENTS
1516         bool
1517         help
1518           See tools/perf/design.txt for details.
1519 
1520 config PERF_USE_VMALLOC
1521         bool
1522         help
1523           See tools/perf/design.txt for details
1524 
1525 menu "Kernel Performance Events And Counters"
1526 
1527 config PERF_EVENTS
1528         bool "Kernel performance events and counters"
1529         default y if PROFILING
1530         depends on HAVE_PERF_EVENTS
1531         select ANON_INODES
1532         select IRQ_WORK
1533         help
1534           Enable kernel support for various performance events provided
1535           by software and hardware.
1536 
1537           Software events are supported either built-in or via the
1538           use of generic tracepoints.
1539 
1540           Most modern CPUs support performance events via performance
1541           counter registers. These registers count the number of certain
1542           types of hw events: such as instructions executed, cachemisses
1543           suffered, or branches mis-predicted - without slowing down the
1544           kernel or applications. These registers can also trigger interrupts
1545           when a threshold number of events have passed - and can thus be
1546           used to profile the code that runs on that CPU.
1547 
1548           The Linux Performance Event subsystem provides an abstraction of
1549           these software and hardware event capabilities, available via a
1550           system call and used by the "perf" utility in tools/perf/. It
1551           provides per task and per CPU counters, and it provides event
1552           capabilities on top of those.
1553 
1554           Say Y if unsure.
1555 
1556 config DEBUG_PERF_USE_VMALLOC
1557         default n
1558         bool "Debug: use vmalloc to back perf mmap() buffers"
1559         depends on PERF_EVENTS && DEBUG_KERNEL
1560         select PERF_USE_VMALLOC
1561         help
1562          Use vmalloc memory to back perf mmap() buffers.
1563 
1564          Mostly useful for debugging the vmalloc code on platforms
1565          that don't require it.
1566 
1567          Say N if unsure.
1568 
1569 endmenu
1570 
1571 config VM_EVENT_COUNTERS
1572         default y
1573         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1574         help
1575           VM event counters are needed for event counts to be shown.
1576           This option allows the disabling of the VM event counters
1577           on EXPERT systems.  /proc/vmstat will only show page counts
1578           if VM event counters are disabled.
1579 
1580 config SLUB_DEBUG
1581         default y
1582         bool "Enable SLUB debugging support" if EXPERT
1583         depends on SLUB && SYSFS
1584         help
1585           SLUB has extensive debug support features. Disabling these can
1586           result in significant savings in code size. This also disables
1587           SLUB sysfs support. /sys/slab will not exist and there will be
1588           no support for cache validation etc.
1589 
1590 config COMPAT_BRK
1591         bool "Disable heap randomization"
1592         default y
1593         help
1594           Randomizing heap placement makes heap exploits harder, but it
1595           also breaks ancient binaries (including anything libc5 based).
1596           This option changes the bootup default to heap randomization
1597           disabled, and can be overridden at runtime by setting
1598           /proc/sys/kernel/randomize_va_space to 2.
1599 
1600           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1601 
1602 choice
1603         prompt "Choose SLAB allocator"
1604         default SLUB
1605         help
1606            This option allows to select a slab allocator.
1607 
1608 config SLAB
1609         bool "SLAB"
1610         help
1611           The regular slab allocator that is established and known to work
1612           well in all environments. It organizes cache hot objects in
1613           per cpu and per node queues.
1614 
1615 config SLUB
1616         bool "SLUB (Unqueued Allocator)"
1617         help
1618            SLUB is a slab allocator that minimizes cache line usage
1619            instead of managing queues of cached objects (SLAB approach).
1620            Per cpu caching is realized using slabs of objects instead
1621            of queues of objects. SLUB can use memory efficiently
1622            and has enhanced diagnostics. SLUB is the default choice for
1623            a slab allocator.
1624 
1625 config SLOB
1626         depends on EXPERT
1627         bool "SLOB (Simple Allocator)"
1628         help
1629            SLOB replaces the stock allocator with a drastically simpler
1630            allocator. SLOB is generally more space efficient but
1631            does not perform as well on large systems.
1632 
1633 endchoice
1634 
1635 config SLUB_CPU_PARTIAL
1636         default y
1637         depends on SLUB && SMP
1638         bool "SLUB per cpu partial cache"
1639         help
1640           Per cpu partial caches accellerate objects allocation and freeing
1641           that is local to a processor at the price of more indeterminism
1642           in the latency of the free. On overflow these caches will be cleared
1643           which requires the taking of locks that may cause latency spikes.
1644           Typically one would choose no for a realtime system.
1645 
1646 config MMAP_ALLOW_UNINITIALIZED
1647         bool "Allow mmapped anonymous memory to be uninitialized"
1648         depends on EXPERT && !MMU
1649         default n
1650         help
1651           Normally, and according to the Linux spec, anonymous memory obtained
1652           from mmap() has it's contents cleared before it is passed to
1653           userspace.  Enabling this config option allows you to request that
1654           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1655           providing a huge performance boost.  If this option is not enabled,
1656           then the flag will be ignored.
1657 
1658           This is taken advantage of by uClibc's malloc(), and also by
1659           ELF-FDPIC binfmt's brk and stack allocator.
1660 
1661           Because of the obvious security issues, this option should only be
1662           enabled on embedded devices where you control what is run in
1663           userspace.  Since that isn't generally a problem on no-MMU systems,
1664           it is normally safe to say Y here.
1665 
1666           See Documentation/nommu-mmap.txt for more information.
1667 
1668 config SYSTEM_TRUSTED_KEYRING
1669         bool "Provide system-wide ring of trusted keys"
1670         depends on KEYS
1671         help
1672           Provide a system keyring to which trusted keys can be added.  Keys in
1673           the keyring are considered to be trusted.  Keys may be added at will
1674           by the kernel from compiled-in data and from hardware key stores, but
1675           userspace may only add extra keys if those keys can be verified by
1676           keys already in the keyring.
1677 
1678           Keys in this keyring are used by module signature checking.
1679 
1680 config PROFILING
1681         bool "Profiling support"
1682         help
1683           Say Y here to enable the extended profiling support mechanisms used
1684           by profilers such as OProfile.
1685 
1686 #
1687 # Place an empty function call at each tracepoint site. Can be
1688 # dynamically changed for a probe function.
1689 #
1690 config TRACEPOINTS
1691         bool
1692 
1693 source "arch/Kconfig"
1694 
1695 endmenu         # General setup
1696 
1697 config HAVE_GENERIC_DMA_COHERENT
1698         bool
1699         default n
1700 
1701 config SLABINFO
1702         bool
1703         depends on PROC_FS
1704         depends on SLAB || SLUB_DEBUG
1705         default y
1706 
1707 config RT_MUTEXES
1708         boolean
1709 
1710 config BASE_SMALL
1711         int
1712         default 0 if BASE_FULL
1713         default 1 if !BASE_FULL
1714 
1715 menuconfig MODULES
1716         bool "Enable loadable module support"
1717         option modules
1718         help
1719           Kernel modules are small pieces of compiled code which can
1720           be inserted in the running kernel, rather than being
1721           permanently built into the kernel.  You use the "modprobe"
1722           tool to add (and sometimes remove) them.  If you say Y here,
1723           many parts of the kernel can be built as modules (by
1724           answering M instead of Y where indicated): this is most
1725           useful for infrequently used options which are not required
1726           for booting.  For more information, see the man pages for
1727           modprobe, lsmod, modinfo, insmod and rmmod.
1728 
1729           If you say Y here, you will need to run "make
1730           modules_install" to put the modules under /lib/modules/
1731           where modprobe can find them (you may need to be root to do
1732           this).
1733 
1734           If unsure, say Y.
1735 
1736 if MODULES
1737 
1738 config MODULE_FORCE_LOAD
1739         bool "Forced module loading"
1740         default n
1741         help
1742           Allow loading of modules without version information (ie. modprobe
1743           --force).  Forced module loading sets the 'F' (forced) taint flag and
1744           is usually a really bad idea.
1745 
1746 config MODULE_UNLOAD
1747         bool "Module unloading"
1748         help
1749           Without this option you will not be able to unload any
1750           modules (note that some modules may not be unloadable
1751           anyway), which makes your kernel smaller, faster
1752           and simpler.  If unsure, say Y.
1753 
1754 config MODULE_FORCE_UNLOAD
1755         bool "Forced module unloading"
1756         depends on MODULE_UNLOAD
1757         help
1758           This option allows you to force a module to unload, even if the
1759           kernel believes it is unsafe: the kernel will remove the module
1760           without waiting for anyone to stop using it (using the -f option to
1761           rmmod).  This is mainly for kernel developers and desperate users.
1762           If unsure, say N.
1763 
1764 config MODVERSIONS
1765         bool "Module versioning support"
1766         help
1767           Usually, you have to use modules compiled with your kernel.
1768           Saying Y here makes it sometimes possible to use modules
1769           compiled for different kernels, by adding enough information
1770           to the modules to (hopefully) spot any changes which would
1771           make them incompatible with the kernel you are running.  If
1772           unsure, say N.
1773 
1774 config MODULE_SRCVERSION_ALL
1775         bool "Source checksum for all modules"
1776         help
1777           Modules which contain a MODULE_VERSION get an extra "srcversion"
1778           field inserted into their modinfo section, which contains a
1779           sum of the source files which made it.  This helps maintainers
1780           see exactly which source was used to build a module (since
1781           others sometimes change the module source without updating
1782           the version).  With this option, such a "srcversion" field
1783           will be created for all modules.  If unsure, say N.
1784 
1785 config MODULE_SIG
1786         bool "Module signature verification"
1787         depends on MODULES
1788         select SYSTEM_TRUSTED_KEYRING
1789         select KEYS
1790         select CRYPTO
1791         select ASYMMETRIC_KEY_TYPE
1792         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1793         select PUBLIC_KEY_ALGO_RSA
1794         select ASN1
1795         select OID_REGISTRY
1796         select X509_CERTIFICATE_PARSER
1797         help
1798           Check modules for valid signatures upon load: the signature
1799           is simply appended to the module. For more information see
1800           Documentation/module-signing.txt.
1801 
1802           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1803           module DOES NOT get stripped after being signed.  This includes the
1804           debuginfo strip done by some packagers (such as rpmbuild) and
1805           inclusion into an initramfs that wants the module size reduced.
1806 
1807 config MODULE_SIG_FORCE
1808         bool "Require modules to be validly signed"
1809         depends on MODULE_SIG
1810         help
1811           Reject unsigned modules or signed modules for which we don't have a
1812           key.  Without this, such modules will simply taint the kernel.
1813 
1814 config MODULE_SIG_ALL
1815         bool "Automatically sign all modules"
1816         default y
1817         depends on MODULE_SIG
1818         help
1819           Sign all modules during make modules_install. Without this option,
1820           modules must be signed manually, using the scripts/sign-file tool.
1821 
1822 comment "Do not forget to sign required modules with scripts/sign-file"
1823         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1824 
1825 choice
1826         prompt "Which hash algorithm should modules be signed with?"
1827         depends on MODULE_SIG
1828         help
1829           This determines which sort of hashing algorithm will be used during
1830           signature generation.  This algorithm _must_ be built into the kernel
1831           directly so that signature verification can take place.  It is not
1832           possible to load a signed module containing the algorithm to check
1833           the signature on that module.
1834 
1835 config MODULE_SIG_SHA1
1836         bool "Sign modules with SHA-1"
1837         select CRYPTO_SHA1
1838 
1839 config MODULE_SIG_SHA224
1840         bool "Sign modules with SHA-224"
1841         select CRYPTO_SHA256
1842 
1843 config MODULE_SIG_SHA256
1844         bool "Sign modules with SHA-256"
1845         select CRYPTO_SHA256
1846 
1847 config MODULE_SIG_SHA384
1848         bool "Sign modules with SHA-384"
1849         select CRYPTO_SHA512
1850 
1851 config MODULE_SIG_SHA512
1852         bool "Sign modules with SHA-512"
1853         select CRYPTO_SHA512
1854 
1855 endchoice
1856 
1857 config MODULE_SIG_HASH
1858         string
1859         depends on MODULE_SIG
1860         default "sha1" if MODULE_SIG_SHA1
1861         default "sha224" if MODULE_SIG_SHA224
1862         default "sha256" if MODULE_SIG_SHA256
1863         default "sha384" if MODULE_SIG_SHA384
1864         default "sha512" if MODULE_SIG_SHA512
1865 
1866 endif # MODULES
1867 
1868 config INIT_ALL_POSSIBLE
1869         bool
1870         help
1871           Back when each arch used to define their own cpu_online_mask and
1872           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1873           with all 1s, and others with all 0s.  When they were centralised,
1874           it was better to provide this option than to break all the archs
1875           and have several arch maintainers pursuing me down dark alleys.
1876 
1877 config STOP_MACHINE
1878         bool
1879         default y
1880         depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1881         help
1882           Need stop_machine() primitive.
1883 
1884 source "block/Kconfig"
1885 
1886 config PREEMPT_NOTIFIERS
1887         bool
1888 
1889 config PADATA
1890         depends on SMP
1891         bool
1892 
1893 # Can be selected by architectures with broken toolchains
1894 # that get confused by correct const<->read_only section
1895 # mappings
1896 config BROKEN_RODATA
1897         bool
1898 
1899 config ASN1
1900         tristate
1901         help
1902           Build a simple ASN.1 grammar compiler that produces a bytecode output
1903           that can be interpreted by the ASN.1 stream decoder and used to
1904           inform it as to what tags are to be expected in a stream and what
1905           functions to call on what tags.
1906 
1907 source "kernel/Kconfig.locks"

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