Version:  2.0.40 2.2.26 2.4.37 2.6.39 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

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 FHANDLE
265         bool "open by fhandle syscalls"
266         select EXPORTFS
267         help
268           If you say Y here, a user level program will be able to map
269           file names to handle and then later use the handle for
270           different file system operations. This is useful in implementing
271           userspace file servers, which now track files using handles instead
272           of names. The handle would remain the same even if file names
273           get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
274           syscalls.
275 
276 config USELIB
277         bool "uselib syscall"
278         default y
279         help
280           This option enables the uselib syscall, a system call used in the
281           dynamic linker from libc5 and earlier.  glibc does not use this
282           system call.  If you intend to run programs built on libc5 or
283           earlier, you may need to enable this syscall.  Current systems
284           running glibc can safely disable this.
285 
286 config AUDIT
287         bool "Auditing support"
288         depends on NET
289         help
290           Enable auditing infrastructure that can be used with another
291           kernel subsystem, such as SELinux (which requires this for
292           logging of avc messages output).  Does not do system-call
293           auditing without CONFIG_AUDITSYSCALL.
294 
295 config HAVE_ARCH_AUDITSYSCALL
296         bool
297 
298 config AUDITSYSCALL
299         bool "Enable system-call auditing support"
300         depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
301         default y if SECURITY_SELINUX
302         help
303           Enable low-overhead system-call auditing infrastructure that
304           can be used independently or with another kernel subsystem,
305           such as SELinux.
306 
307 config AUDIT_WATCH
308         def_bool y
309         depends on AUDITSYSCALL
310         select FSNOTIFY
311 
312 config AUDIT_TREE
313         def_bool y
314         depends on AUDITSYSCALL
315         select FSNOTIFY
316 
317 source "kernel/irq/Kconfig"
318 source "kernel/time/Kconfig"
319 
320 menu "CPU/Task time and stats accounting"
321 
322 config VIRT_CPU_ACCOUNTING
323         bool
324 
325 choice
326         prompt "Cputime accounting"
327         default TICK_CPU_ACCOUNTING if !PPC64
328         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
329 
330 # Kind of a stub config for the pure tick based cputime accounting
331 config TICK_CPU_ACCOUNTING
332         bool "Simple tick based cputime accounting"
333         depends on !S390 && !NO_HZ_FULL
334         help
335           This is the basic tick based cputime accounting that maintains
336           statistics about user, system and idle time spent on per jiffies
337           granularity.
338 
339           If unsure, say Y.
340 
341 config VIRT_CPU_ACCOUNTING_NATIVE
342         bool "Deterministic task and CPU time accounting"
343         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
344         select VIRT_CPU_ACCOUNTING
345         help
346           Select this option to enable more accurate task and CPU time
347           accounting.  This is done by reading a CPU counter on each
348           kernel entry and exit and on transitions within the kernel
349           between system, softirq and hardirq state, so there is a
350           small performance impact.  In the case of s390 or IBM POWER > 5,
351           this also enables accounting of stolen time on logically-partitioned
352           systems.
353 
354 config VIRT_CPU_ACCOUNTING_GEN
355         bool "Full dynticks CPU time accounting"
356         depends on HAVE_CONTEXT_TRACKING
357         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
358         select VIRT_CPU_ACCOUNTING
359         select CONTEXT_TRACKING
360         help
361           Select this option to enable task and CPU time accounting on full
362           dynticks systems. This accounting is implemented by watching every
363           kernel-user boundaries using the context tracking subsystem.
364           The accounting is thus performed at the expense of some significant
365           overhead.
366 
367           For now this is only useful if you are working on the full
368           dynticks subsystem development.
369 
370           If unsure, say N.
371 
372 config IRQ_TIME_ACCOUNTING
373         bool "Fine granularity task level IRQ time accounting"
374         depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
375         help
376           Select this option to enable fine granularity task irq time
377           accounting. This is done by reading a timestamp on each
378           transitions between softirq and hardirq state, so there can be a
379           small performance impact.
380 
381           If in doubt, say N here.
382 
383 endchoice
384 
385 config BSD_PROCESS_ACCT
386         bool "BSD Process Accounting"
387         help
388           If you say Y here, a user level program will be able to instruct the
389           kernel (via a special system call) to write process accounting
390           information to a file: whenever a process exits, information about
391           that process will be appended to the file by the kernel.  The
392           information includes things such as creation time, owning user,
393           command name, memory usage, controlling terminal etc. (the complete
394           list is in the struct acct in <file:include/linux/acct.h>).  It is
395           up to the user level program to do useful things with this
396           information.  This is generally a good idea, so say Y.
397 
398 config BSD_PROCESS_ACCT_V3
399         bool "BSD Process Accounting version 3 file format"
400         depends on BSD_PROCESS_ACCT
401         default n
402         help
403           If you say Y here, the process accounting information is written
404           in a new file format that also logs the process IDs of each
405           process and it's parent. Note that this file format is incompatible
406           with previous v0/v1/v2 file formats, so you will need updated tools
407           for processing it. A preliminary version of these tools is available
408           at <http://www.gnu.org/software/acct/>.
409 
410 config TASKSTATS
411         bool "Export task/process statistics through netlink"
412         depends on NET
413         default n
414         help
415           Export selected statistics for tasks/processes through the
416           generic netlink interface. Unlike BSD process accounting, the
417           statistics are available during the lifetime of tasks/processes as
418           responses to commands. Like BSD accounting, they are sent to user
419           space on task exit.
420 
421           Say N if unsure.
422 
423 config TASK_DELAY_ACCT
424         bool "Enable per-task delay accounting"
425         depends on TASKSTATS
426         help
427           Collect information on time spent by a task waiting for system
428           resources like cpu, synchronous block I/O completion and swapping
429           in pages. Such statistics can help in setting a task's priorities
430           relative to other tasks for cpu, io, rss limits etc.
431 
432           Say N if unsure.
433 
434 config TASK_XACCT
435         bool "Enable extended accounting over taskstats"
436         depends on TASKSTATS
437         help
438           Collect extended task accounting data and send the data
439           to userland for processing over the taskstats interface.
440 
441           Say N if unsure.
442 
443 config TASK_IO_ACCOUNTING
444         bool "Enable per-task storage I/O accounting"
445         depends on TASK_XACCT
446         help
447           Collect information on the number of bytes of storage I/O which this
448           task has caused.
449 
450           Say N if unsure.
451 
452 endmenu # "CPU/Task time and stats accounting"
453 
454 menu "RCU Subsystem"
455 
456 choice
457         prompt "RCU Implementation"
458         default TREE_RCU
459 
460 config TREE_RCU
461         bool "Tree-based hierarchical RCU"
462         depends on !PREEMPT && SMP
463         select IRQ_WORK
464         help
465           This option selects the RCU implementation that is
466           designed for very large SMP system with hundreds or
467           thousands of CPUs.  It also scales down nicely to
468           smaller systems.
469 
470 config TREE_PREEMPT_RCU
471         bool "Preemptible tree-based hierarchical RCU"
472         depends on PREEMPT
473         select IRQ_WORK
474         help
475           This option selects the RCU implementation that is
476           designed for very large SMP systems with hundreds or
477           thousands of CPUs, but for which real-time response
478           is also required.  It also scales down nicely to
479           smaller systems.
480 
481           Select this option if you are unsure.
482 
483 config TINY_RCU
484         bool "UP-only small-memory-footprint RCU"
485         depends on !PREEMPT && !SMP
486         help
487           This option selects the RCU implementation that is
488           designed for UP systems from which real-time response
489           is not required.  This option greatly reduces the
490           memory footprint of RCU.
491 
492 endchoice
493 
494 config PREEMPT_RCU
495         def_bool TREE_PREEMPT_RCU
496         help
497           This option enables preemptible-RCU code that is common between
498           the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
499 
500 config RCU_STALL_COMMON
501         def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
502         help
503           This option enables RCU CPU stall code that is common between
504           the TINY and TREE variants of RCU.  The purpose is to allow
505           the tiny variants to disable RCU CPU stall warnings, while
506           making these warnings mandatory for the tree variants.
507 
508 config CONTEXT_TRACKING
509        bool
510 
511 config RCU_USER_QS
512         bool "Consider userspace as in RCU extended quiescent state"
513         depends on HAVE_CONTEXT_TRACKING && SMP
514         select CONTEXT_TRACKING
515         help
516           This option sets hooks on kernel / userspace boundaries and
517           puts RCU in extended quiescent state when the CPU runs in
518           userspace. It means that when a CPU runs in userspace, it is
519           excluded from the global RCU state machine and thus doesn't
520           try to keep the timer tick on for RCU.
521 
522           Unless you want to hack and help the development of the full
523           dynticks mode, you shouldn't enable this option.  It also
524           adds unnecessary overhead.
525 
526           If unsure say N
527 
528 config CONTEXT_TRACKING_FORCE
529         bool "Force context tracking"
530         depends on CONTEXT_TRACKING
531         default y if !NO_HZ_FULL
532         help
533           The major pre-requirement for full dynticks to work is to
534           support the context tracking subsystem. But there are also
535           other dependencies to provide in order to make the full
536           dynticks working.
537 
538           This option stands for testing when an arch implements the
539           context tracking backend but doesn't yet fullfill all the
540           requirements to make the full dynticks feature working.
541           Without the full dynticks, there is no way to test the support
542           for context tracking and the subsystems that rely on it: RCU
543           userspace extended quiescent state and tickless cputime
544           accounting. This option copes with the absence of the full
545           dynticks subsystem by forcing the context tracking on all
546           CPUs in the system.
547 
548           Say Y only if you're working on the development of an
549           architecture backend for the context tracking.
550 
551           Say N otherwise, this option brings an overhead that you
552           don't want in production.
553 
554 
555 config RCU_FANOUT
556         int "Tree-based hierarchical RCU fanout value"
557         range 2 64 if 64BIT
558         range 2 32 if !64BIT
559         depends on TREE_RCU || TREE_PREEMPT_RCU
560         default 64 if 64BIT
561         default 32 if !64BIT
562         help
563           This option controls the fanout of hierarchical implementations
564           of RCU, allowing RCU to work efficiently on machines with
565           large numbers of CPUs.  This value must be at least the fourth
566           root of NR_CPUS, which allows NR_CPUS to be insanely large.
567           The default value of RCU_FANOUT should be used for production
568           systems, but if you are stress-testing the RCU implementation
569           itself, small RCU_FANOUT values allow you to test large-system
570           code paths on small(er) systems.
571 
572           Select a specific number if testing RCU itself.
573           Take the default if unsure.
574 
575 config RCU_FANOUT_LEAF
576         int "Tree-based hierarchical RCU leaf-level fanout value"
577         range 2 RCU_FANOUT if 64BIT
578         range 2 RCU_FANOUT if !64BIT
579         depends on TREE_RCU || TREE_PREEMPT_RCU
580         default 16
581         help
582           This option controls the leaf-level fanout of hierarchical
583           implementations of RCU, and allows trading off cache misses
584           against lock contention.  Systems that synchronize their
585           scheduling-clock interrupts for energy-efficiency reasons will
586           want the default because the smaller leaf-level fanout keeps
587           lock contention levels acceptably low.  Very large systems
588           (hundreds or thousands of CPUs) will instead want to set this
589           value to the maximum value possible in order to reduce the
590           number of cache misses incurred during RCU's grace-period
591           initialization.  These systems tend to run CPU-bound, and thus
592           are not helped by synchronized interrupts, and thus tend to
593           skew them, which reduces lock contention enough that large
594           leaf-level fanouts work well.
595 
596           Select a specific number if testing RCU itself.
597 
598           Select the maximum permissible value for large systems.
599 
600           Take the default if unsure.
601 
602 config RCU_FANOUT_EXACT
603         bool "Disable tree-based hierarchical RCU auto-balancing"
604         depends on TREE_RCU || TREE_PREEMPT_RCU
605         default n
606         help
607           This option forces use of the exact RCU_FANOUT value specified,
608           regardless of imbalances in the hierarchy.  This is useful for
609           testing RCU itself, and might one day be useful on systems with
610           strong NUMA behavior.
611 
612           Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
613 
614           Say N if unsure.
615 
616 config RCU_FAST_NO_HZ
617         bool "Accelerate last non-dyntick-idle CPU's grace periods"
618         depends on NO_HZ_COMMON && SMP
619         default n
620         help
621           This option permits CPUs to enter dynticks-idle state even if
622           they have RCU callbacks queued, and prevents RCU from waking
623           these CPUs up more than roughly once every four jiffies (by
624           default, you can adjust this using the rcutree.rcu_idle_gp_delay
625           parameter), thus improving energy efficiency.  On the other
626           hand, this option increases the duration of RCU grace periods,
627           for example, slowing down synchronize_rcu().
628 
629           Say Y if energy efficiency is critically important, and you
630                 don't care about increased grace-period durations.
631 
632           Say N if you are unsure.
633 
634 config TREE_RCU_TRACE
635         def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
636         select DEBUG_FS
637         help
638           This option provides tracing for the TREE_RCU and
639           TREE_PREEMPT_RCU implementations, permitting Makefile to
640           trivially select kernel/rcutree_trace.c.
641 
642 config RCU_BOOST
643         bool "Enable RCU priority boosting"
644         depends on RT_MUTEXES && PREEMPT_RCU
645         default n
646         help
647           This option boosts the priority of preempted RCU readers that
648           block the current preemptible RCU grace period for too long.
649           This option also prevents heavy loads from blocking RCU
650           callback invocation for all flavors of RCU.
651 
652           Say Y here if you are working with real-time apps or heavy loads
653           Say N here if you are unsure.
654 
655 config RCU_BOOST_PRIO
656         int "Real-time priority to boost RCU readers to"
657         range 1 99
658         depends on RCU_BOOST
659         default 1
660         help
661           This option specifies the real-time priority to which long-term
662           preempted RCU readers are to be boosted.  If you are working
663           with a real-time application that has one or more CPU-bound
664           threads running at a real-time priority level, you should set
665           RCU_BOOST_PRIO to a priority higher then the highest-priority
666           real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
667           of 1 is appropriate in the common case, which is real-time
668           applications that do not have any CPU-bound threads.
669 
670           Some real-time applications might not have a single real-time
671           thread that saturates a given CPU, but instead might have
672           multiple real-time threads that, taken together, fully utilize
673           that CPU.  In this case, you should set RCU_BOOST_PRIO to
674           a priority higher than the lowest-priority thread that is
675           conspiring to prevent the CPU from running any non-real-time
676           tasks.  For example, if one thread at priority 10 and another
677           thread at priority 5 are between themselves fully consuming
678           the CPU time on a given CPU, then RCU_BOOST_PRIO should be
679           set to priority 6 or higher.
680 
681           Specify the real-time priority, or take the default if unsure.
682 
683 config RCU_BOOST_DELAY
684         int "Milliseconds to delay boosting after RCU grace-period start"
685         range 0 3000
686         depends on RCU_BOOST
687         default 500
688         help
689           This option specifies the time to wait after the beginning of
690           a given grace period before priority-boosting preempted RCU
691           readers blocking that grace period.  Note that any RCU reader
692           blocking an expedited RCU grace period is boosted immediately.
693 
694           Accept the default if unsure.
695 
696 config RCU_NOCB_CPU
697         bool "Offload RCU callback processing from boot-selected CPUs"
698         depends on TREE_RCU || TREE_PREEMPT_RCU
699         default n
700         help
701           Use this option to reduce OS jitter for aggressive HPC or
702           real-time workloads.  It can also be used to offload RCU
703           callback invocation to energy-efficient CPUs in battery-powered
704           asymmetric multiprocessors.
705 
706           This option offloads callback invocation from the set of
707           CPUs specified at boot time by the rcu_nocbs parameter.
708           For each such CPU, a kthread ("rcuox/N") will be created to
709           invoke callbacks, where the "N" is the CPU being offloaded,
710           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
711           "s" for RCU-sched.  Nothing prevents this kthread from running
712           on the specified CPUs, but (1) the kthreads may be preempted
713           between each callback, and (2) affinity or cgroups can be used
714           to force the kthreads to run on whatever set of CPUs is desired.
715 
716           Say Y here if you want to help to debug reduced OS jitter.
717           Say N here if you are unsure.
718 
719 choice
720         prompt "Build-forced no-CBs CPUs"
721         default RCU_NOCB_CPU_NONE
722         help
723           This option allows no-CBs CPUs (whose RCU callbacks are invoked
724           from kthreads rather than from softirq context) to be specified
725           at build time.  Additional no-CBs CPUs may be specified by
726           the rcu_nocbs= boot parameter.
727 
728 config RCU_NOCB_CPU_NONE
729         bool "No build_forced no-CBs CPUs"
730         depends on RCU_NOCB_CPU && !NO_HZ_FULL
731         help
732           This option does not force any of the CPUs to be no-CBs CPUs.
733           Only CPUs designated by the rcu_nocbs= boot parameter will be
734           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
735           kthreads whose names begin with "rcuo".  All other CPUs will
736           invoke their own RCU callbacks in softirq context.
737 
738           Select this option if you want to choose no-CBs CPUs at
739           boot time, for example, to allow testing of different no-CBs
740           configurations without having to rebuild the kernel each time.
741 
742 config RCU_NOCB_CPU_ZERO
743         bool "CPU 0 is a build_forced no-CBs CPU"
744         depends on RCU_NOCB_CPU && !NO_HZ_FULL
745         help
746           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
747           callbacks are invoked by a per-CPU kthread whose name begins
748           with "rcuo".  Additional CPUs may be designated as no-CBs
749           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
750           All other CPUs will invoke their own RCU callbacks in softirq
751           context.
752 
753           Select this if CPU 0 needs to be a no-CBs CPU for real-time
754           or energy-efficiency reasons, but the real reason it exists
755           is to ensure that randconfig testing covers mixed systems.
756 
757 config RCU_NOCB_CPU_ALL
758         bool "All CPUs are build_forced no-CBs CPUs"
759         depends on RCU_NOCB_CPU
760         help
761           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
762           boot parameter will be ignored.  All CPUs' RCU callbacks will
763           be executed in the context of per-CPU rcuo kthreads created for
764           this purpose.  Assuming that the kthreads whose names start with
765           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
766           on the remaining CPUs, but might decrease memory locality during
767           RCU-callback invocation, thus potentially degrading throughput.
768 
769           Select this if all CPUs need to be no-CBs CPUs for real-time
770           or energy-efficiency reasons.
771 
772 endchoice
773 
774 endmenu # "RCU Subsystem"
775 
776 config IKCONFIG
777         tristate "Kernel .config support"
778         ---help---
779           This option enables the complete Linux kernel ".config" file
780           contents to be saved in the kernel. It provides documentation
781           of which kernel options are used in a running kernel or in an
782           on-disk kernel.  This information can be extracted from the kernel
783           image file with the script scripts/extract-ikconfig and used as
784           input to rebuild the current kernel or to build another kernel.
785           It can also be extracted from a running kernel by reading
786           /proc/config.gz if enabled (below).
787 
788 config IKCONFIG_PROC
789         bool "Enable access to .config through /proc/config.gz"
790         depends on IKCONFIG && PROC_FS
791         ---help---
792           This option enables access to the kernel configuration file
793           through /proc/config.gz.
794 
795 config LOG_BUF_SHIFT
796         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
797         range 12 21
798         default 17
799         help
800           Select kernel log buffer size as a power of 2.
801           Examples:
802                      17 => 128 KB
803                      16 => 64 KB
804                      15 => 32 KB
805                      14 => 16 KB
806                      13 =>  8 KB
807                      12 =>  4 KB
808 
809 #
810 # Architectures with an unreliable sched_clock() should select this:
811 #
812 config HAVE_UNSTABLE_SCHED_CLOCK
813         bool
814 
815 config GENERIC_SCHED_CLOCK
816         bool
817 
818 #
819 # For architectures that want to enable the support for NUMA-affine scheduler
820 # balancing logic:
821 #
822 config ARCH_SUPPORTS_NUMA_BALANCING
823         bool
824 
825 #
826 # For architectures that know their GCC __int128 support is sound
827 #
828 config ARCH_SUPPORTS_INT128
829         bool
830 
831 # For architectures that (ab)use NUMA to represent different memory regions
832 # all cpu-local but of different latencies, such as SuperH.
833 #
834 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
835         bool
836 
837 #
838 # For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
839 config ARCH_WANTS_PROT_NUMA_PROT_NONE
840         bool
841 
842 config ARCH_USES_NUMA_PROT_NONE
843         bool
844         default y
845         depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
846         depends on NUMA_BALANCING
847 
848 config NUMA_BALANCING_DEFAULT_ENABLED
849         bool "Automatically enable NUMA aware memory/task placement"
850         default y
851         depends on NUMA_BALANCING
852         help
853           If set, automatic NUMA balancing will be enabled if running on a NUMA
854           machine.
855 
856 config NUMA_BALANCING
857         bool "Memory placement aware NUMA scheduler"
858         depends on ARCH_SUPPORTS_NUMA_BALANCING
859         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
860         depends on SMP && NUMA && MIGRATION
861         help
862           This option adds support for automatic NUMA aware memory/task placement.
863           The mechanism is quite primitive and is based on migrating memory when
864           it has references to the node the task is running on.
865 
866           This system will be inactive on UMA systems.
867 
868 menuconfig CGROUPS
869         boolean "Control Group support"
870         select KERNFS
871         help
872           This option adds support for grouping sets of processes together, for
873           use with process control subsystems such as Cpusets, CFS, memory
874           controls or device isolation.
875           See
876                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
877                 - Documentation/cgroups/ (features for grouping, isolation
878                                           and resource control)
879 
880           Say N if unsure.
881 
882 if CGROUPS
883 
884 config CGROUP_DEBUG
885         bool "Example debug cgroup subsystem"
886         default n
887         help
888           This option enables a simple cgroup subsystem that
889           exports useful debugging information about the cgroups
890           framework.
891 
892           Say N if unsure.
893 
894 config CGROUP_FREEZER
895         bool "Freezer cgroup subsystem"
896         help
897           Provides a way to freeze and unfreeze all tasks in a
898           cgroup.
899 
900 config CGROUP_DEVICE
901         bool "Device controller for cgroups"
902         help
903           Provides a cgroup implementing whitelists for devices which
904           a process in the cgroup can mknod or open.
905 
906 config CPUSETS
907         bool "Cpuset support"
908         help
909           This option will let you create and manage CPUSETs which
910           allow dynamically partitioning a system into sets of CPUs and
911           Memory Nodes and assigning tasks to run only within those sets.
912           This is primarily useful on large SMP or NUMA systems.
913 
914           Say N if unsure.
915 
916 config PROC_PID_CPUSET
917         bool "Include legacy /proc/<pid>/cpuset file"
918         depends on CPUSETS
919         default y
920 
921 config CGROUP_CPUACCT
922         bool "Simple CPU accounting cgroup subsystem"
923         help
924           Provides a simple Resource Controller for monitoring the
925           total CPU consumed by the tasks in a cgroup.
926 
927 config RESOURCE_COUNTERS
928         bool "Resource counters"
929         help
930           This option enables controller independent resource accounting
931           infrastructure that works with cgroups.
932 
933 config MEMCG
934         bool "Memory Resource Controller for Control Groups"
935         depends on RESOURCE_COUNTERS
936         select MM_OWNER
937         select EVENTFD
938         help
939           Provides a memory resource controller that manages both anonymous
940           memory and page cache. (See Documentation/cgroups/memory.txt)
941 
942           Note that setting this option increases fixed memory overhead
943           associated with each page of memory in the system. By this,
944           8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
945           usage tracking struct at boot. Total amount of this is printed out
946           at boot.
947 
948           Only enable when you're ok with these trade offs and really
949           sure you need the memory resource controller. Even when you enable
950           this, you can set "cgroup_disable=memory" at your boot option to
951           disable memory resource controller and you can avoid overheads.
952           (and lose benefits of memory resource controller)
953 
954           This config option also selects MM_OWNER config option, which
955           could in turn add some fork/exit overhead.
956 
957 config MEMCG_SWAP
958         bool "Memory Resource Controller Swap Extension"
959         depends on MEMCG && SWAP
960         help
961           Add swap management feature to memory resource controller. When you
962           enable this, you can limit mem+swap usage per cgroup. In other words,
963           when you disable this, memory resource controller has no cares to
964           usage of swap...a process can exhaust all of the swap. This extension
965           is useful when you want to avoid exhaustion swap but this itself
966           adds more overheads and consumes memory for remembering information.
967           Especially if you use 32bit system or small memory system, please
968           be careful about enabling this. When memory resource controller
969           is disabled by boot option, this will be automatically disabled and
970           there will be no overhead from this. Even when you set this config=y,
971           if boot option "swapaccount=0" is set, swap will not be accounted.
972           Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
973           size is 4096bytes, 512k per 1Gbytes of swap.
974 config MEMCG_SWAP_ENABLED
975         bool "Memory Resource Controller Swap Extension enabled by default"
976         depends on MEMCG_SWAP
977         default y
978         help
979           Memory Resource Controller Swap Extension comes with its price in
980           a bigger memory consumption. General purpose distribution kernels
981           which want to enable the feature but keep it disabled by default
982           and let the user enable it by swapaccount=1 boot command line
983           parameter should have this option unselected.
984           For those who want to have the feature enabled by default should
985           select this option (if, for some reason, they need to disable it
986           then swapaccount=0 does the trick).
987 config MEMCG_KMEM
988         bool "Memory Resource Controller Kernel Memory accounting"
989         depends on MEMCG
990         depends on SLUB || SLAB
991         help
992           The Kernel Memory extension for Memory Resource Controller can limit
993           the amount of memory used by kernel objects in the system. Those are
994           fundamentally different from the entities handled by the standard
995           Memory Controller, which are page-based, and can be swapped. Users of
996           the kmem extension can use it to guarantee that no group of processes
997           will ever exhaust kernel resources alone.
998 
999 config CGROUP_HUGETLB
1000         bool "HugeTLB Resource Controller for Control Groups"
1001         depends on RESOURCE_COUNTERS && HUGETLB_PAGE
1002         default n
1003         help
1004           Provides a cgroup Resource Controller for HugeTLB pages.
1005           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1006           The limit is enforced during page fault. Since HugeTLB doesn't
1007           support page reclaim, enforcing the limit at page fault time implies
1008           that, the application will get SIGBUS signal if it tries to access
1009           HugeTLB pages beyond its limit. This requires the application to know
1010           beforehand how much HugeTLB pages it would require for its use. The
1011           control group is tracked in the third page lru pointer. This means
1012           that we cannot use the controller with huge page less than 3 pages.
1013 
1014 config CGROUP_PERF
1015         bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1016         depends on PERF_EVENTS && CGROUPS
1017         help
1018           This option extends the per-cpu mode to restrict monitoring to
1019           threads which belong to the cgroup specified and run on the
1020           designated cpu.
1021 
1022           Say N if unsure.
1023 
1024 menuconfig CGROUP_SCHED
1025         bool "Group CPU scheduler"
1026         default n
1027         help
1028           This feature lets CPU scheduler recognize task groups and control CPU
1029           bandwidth allocation to such task groups. It uses cgroups to group
1030           tasks.
1031 
1032 if CGROUP_SCHED
1033 config FAIR_GROUP_SCHED
1034         bool "Group scheduling for SCHED_OTHER"
1035         depends on CGROUP_SCHED
1036         default CGROUP_SCHED
1037 
1038 config CFS_BANDWIDTH
1039         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1040         depends on FAIR_GROUP_SCHED
1041         default n
1042         help
1043           This option allows users to define CPU bandwidth rates (limits) for
1044           tasks running within the fair group scheduler.  Groups with no limit
1045           set are considered to be unconstrained and will run with no
1046           restriction.
1047           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1048 
1049 config RT_GROUP_SCHED
1050         bool "Group scheduling for SCHED_RR/FIFO"
1051         depends on CGROUP_SCHED
1052         default n
1053         help
1054           This feature lets you explicitly allocate real CPU bandwidth
1055           to task groups. If enabled, it will also make it impossible to
1056           schedule realtime tasks for non-root users until you allocate
1057           realtime bandwidth for them.
1058           See Documentation/scheduler/sched-rt-group.txt for more information.
1059 
1060 endif #CGROUP_SCHED
1061 
1062 config BLK_CGROUP
1063         bool "Block IO controller"
1064         depends on BLOCK
1065         default n
1066         ---help---
1067         Generic block IO controller cgroup interface. This is the common
1068         cgroup interface which should be used by various IO controlling
1069         policies.
1070 
1071         Currently, CFQ IO scheduler uses it to recognize task groups and
1072         control disk bandwidth allocation (proportional time slice allocation)
1073         to such task groups. It is also used by bio throttling logic in
1074         block layer to implement upper limit in IO rates on a device.
1075 
1076         This option only enables generic Block IO controller infrastructure.
1077         One needs to also enable actual IO controlling logic/policy. For
1078         enabling proportional weight division of disk bandwidth in CFQ, set
1079         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1080         CONFIG_BLK_DEV_THROTTLING=y.
1081 
1082         See Documentation/cgroups/blkio-controller.txt for more information.
1083 
1084 config DEBUG_BLK_CGROUP
1085         bool "Enable Block IO controller debugging"
1086         depends on BLK_CGROUP
1087         default n
1088         ---help---
1089         Enable some debugging help. Currently it exports additional stat
1090         files in a cgroup which can be useful for debugging.
1091 
1092 endif # CGROUPS
1093 
1094 config CHECKPOINT_RESTORE
1095         bool "Checkpoint/restore support" if EXPERT
1096         default n
1097         help
1098           Enables additional kernel features in a sake of checkpoint/restore.
1099           In particular it adds auxiliary prctl codes to setup process text,
1100           data and heap segment sizes, and a few additional /proc filesystem
1101           entries.
1102 
1103           If unsure, say N here.
1104 
1105 menuconfig NAMESPACES
1106         bool "Namespaces support" if EXPERT
1107         default !EXPERT
1108         help
1109           Provides the way to make tasks work with different objects using
1110           the same id. For example same IPC id may refer to different objects
1111           or same user id or pid may refer to different tasks when used in
1112           different namespaces.
1113 
1114 if NAMESPACES
1115 
1116 config UTS_NS
1117         bool "UTS namespace"
1118         default y
1119         help
1120           In this namespace tasks see different info provided with the
1121           uname() system call
1122 
1123 config IPC_NS
1124         bool "IPC namespace"
1125         depends on (SYSVIPC || POSIX_MQUEUE)
1126         default y
1127         help
1128           In this namespace tasks work with IPC ids which correspond to
1129           different IPC objects in different namespaces.
1130 
1131 config USER_NS
1132         bool "User namespace"
1133         default n
1134         help
1135           This allows containers, i.e. vservers, to use user namespaces
1136           to provide different user info for different servers.
1137 
1138           When user namespaces are enabled in the kernel it is
1139           recommended that the MEMCG and MEMCG_KMEM options also be
1140           enabled and that user-space use the memory control groups to
1141           limit the amount of memory a memory unprivileged users can
1142           use.
1143 
1144           If unsure, say N.
1145 
1146 config PID_NS
1147         bool "PID Namespaces"
1148         default y
1149         help
1150           Support process id namespaces.  This allows having multiple
1151           processes with the same pid as long as they are in different
1152           pid namespaces.  This is a building block of containers.
1153 
1154 config NET_NS
1155         bool "Network namespace"
1156         depends on NET
1157         default y
1158         help
1159           Allow user space to create what appear to be multiple instances
1160           of the network stack.
1161 
1162 endif # NAMESPACES
1163 
1164 config SCHED_AUTOGROUP
1165         bool "Automatic process group scheduling"
1166         select CGROUPS
1167         select CGROUP_SCHED
1168         select FAIR_GROUP_SCHED
1169         help
1170           This option optimizes the scheduler for common desktop workloads by
1171           automatically creating and populating task groups.  This separation
1172           of workloads isolates aggressive CPU burners (like build jobs) from
1173           desktop applications.  Task group autogeneration is currently based
1174           upon task session.
1175 
1176 config MM_OWNER
1177         bool
1178 
1179 config SYSFS_DEPRECATED
1180         bool "Enable deprecated sysfs features to support old userspace tools"
1181         depends on SYSFS
1182         default n
1183         help
1184           This option adds code that switches the layout of the "block" class
1185           devices, to not show up in /sys/class/block/, but only in
1186           /sys/block/.
1187 
1188           This switch is only active when the sysfs.deprecated=1 boot option is
1189           passed or the SYSFS_DEPRECATED_V2 option is set.
1190 
1191           This option allows new kernels to run on old distributions and tools,
1192           which might get confused by /sys/class/block/. Since 2007/2008 all
1193           major distributions and tools handle this just fine.
1194 
1195           Recent distributions and userspace tools after 2009/2010 depend on
1196           the existence of /sys/class/block/, and will not work with this
1197           option enabled.
1198 
1199           Only if you are using a new kernel on an old distribution, you might
1200           need to say Y here.
1201 
1202 config SYSFS_DEPRECATED_V2
1203         bool "Enable deprecated sysfs features by default"
1204         default n
1205         depends on SYSFS
1206         depends on SYSFS_DEPRECATED
1207         help
1208           Enable deprecated sysfs by default.
1209 
1210           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1211           option.
1212 
1213           Only if you are using a new kernel on an old distribution, you might
1214           need to say Y here. Even then, odds are you would not need it
1215           enabled, you can always pass the boot option if absolutely necessary.
1216 
1217 config RELAY
1218         bool "Kernel->user space relay support (formerly relayfs)"
1219         help
1220           This option enables support for relay interface support in
1221           certain file systems (such as debugfs).
1222           It is designed to provide an efficient mechanism for tools and
1223           facilities to relay large amounts of data from kernel space to
1224           user space.
1225 
1226           If unsure, say N.
1227 
1228 config BLK_DEV_INITRD
1229         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1230         depends on BROKEN || !FRV
1231         help
1232           The initial RAM filesystem is a ramfs which is loaded by the
1233           boot loader (loadlin or lilo) and that is mounted as root
1234           before the normal boot procedure. It is typically used to
1235           load modules needed to mount the "real" root file system,
1236           etc. See <file:Documentation/initrd.txt> for details.
1237 
1238           If RAM disk support (BLK_DEV_RAM) is also included, this
1239           also enables initial RAM disk (initrd) support and adds
1240           15 Kbytes (more on some other architectures) to the kernel size.
1241 
1242           If unsure say Y.
1243 
1244 if BLK_DEV_INITRD
1245 
1246 source "usr/Kconfig"
1247 
1248 endif
1249 
1250 config CC_OPTIMIZE_FOR_SIZE
1251         bool "Optimize for size"
1252         help
1253           Enabling this option will pass "-Os" instead of "-O2" to gcc
1254           resulting in a smaller kernel.
1255 
1256           If unsure, say N.
1257 
1258 config SYSCTL
1259         bool
1260 
1261 config ANON_INODES
1262         bool
1263 
1264 config HAVE_UID16
1265         bool
1266 
1267 config SYSCTL_EXCEPTION_TRACE
1268         bool
1269         help
1270           Enable support for /proc/sys/debug/exception-trace.
1271 
1272 config SYSCTL_ARCH_UNALIGN_NO_WARN
1273         bool
1274         help
1275           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1276           Allows arch to define/use @no_unaligned_warning to possibly warn
1277           about unaligned access emulation going on under the hood.
1278 
1279 config SYSCTL_ARCH_UNALIGN_ALLOW
1280         bool
1281         help
1282           Enable support for /proc/sys/kernel/unaligned-trap
1283           Allows arches to define/use @unaligned_enabled to runtime toggle
1284           the unaligned access emulation.
1285           see arch/parisc/kernel/unaligned.c for reference
1286 
1287 config HAVE_PCSPKR_PLATFORM
1288         bool
1289 
1290 menuconfig EXPERT
1291         bool "Configure standard kernel features (expert users)"
1292         # Unhide debug options, to make the on-by-default options visible
1293         select DEBUG_KERNEL
1294         help
1295           This option allows certain base kernel options and settings
1296           to be disabled or tweaked. This is for specialized
1297           environments which can tolerate a "non-standard" kernel.
1298           Only use this if you really know what you are doing.
1299 
1300 config UID16
1301         bool "Enable 16-bit UID system calls" if EXPERT
1302         depends on HAVE_UID16
1303         default y
1304         help
1305           This enables the legacy 16-bit UID syscall wrappers.
1306 
1307 config SYSFS_SYSCALL
1308         bool "Sysfs syscall support" if EXPERT
1309         default y
1310         ---help---
1311           sys_sysfs is an obsolete system call no longer supported in libc.
1312           Note that disabling this option is more secure but might break
1313           compatibility with some systems.
1314 
1315           If unsure say Y here.
1316 
1317 config SYSCTL_SYSCALL
1318         bool "Sysctl syscall support" if EXPERT
1319         depends on PROC_SYSCTL
1320         default n
1321         select SYSCTL
1322         ---help---
1323           sys_sysctl uses binary paths that have been found challenging
1324           to properly maintain and use.  The interface in /proc/sys
1325           using paths with ascii names is now the primary path to this
1326           information.
1327 
1328           Almost nothing using the binary sysctl interface so if you are
1329           trying to save some space it is probably safe to disable this,
1330           making your kernel marginally smaller.
1331 
1332           If unsure say N here.
1333 
1334 config KALLSYMS
1335          bool "Load all symbols for debugging/ksymoops" if EXPERT
1336          default y
1337          help
1338            Say Y here to let the kernel print out symbolic crash information and
1339            symbolic stack backtraces. This increases the size of the kernel
1340            somewhat, as all symbols have to be loaded into the kernel image.
1341 
1342 config KALLSYMS_ALL
1343         bool "Include all symbols in kallsyms"
1344         depends on DEBUG_KERNEL && KALLSYMS
1345         help
1346            Normally kallsyms only contains the symbols of functions for nicer
1347            OOPS messages and backtraces (i.e., symbols from the text and inittext
1348            sections). This is sufficient for most cases. And only in very rare
1349            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1350            names of variables from the data sections, etc).
1351 
1352            This option makes sure that all symbols are loaded into the kernel
1353            image (i.e., symbols from all sections) in cost of increased kernel
1354            size (depending on the kernel configuration, it may be 300KiB or
1355            something like this).
1356 
1357            Say N unless you really need all symbols.
1358 
1359 config PRINTK
1360         default y
1361         bool "Enable support for printk" if EXPERT
1362         select IRQ_WORK
1363         help
1364           This option enables normal printk support. Removing it
1365           eliminates most of the message strings from the kernel image
1366           and makes the kernel more or less silent. As this makes it
1367           very difficult to diagnose system problems, saying N here is
1368           strongly discouraged.
1369 
1370 config BUG
1371         bool "BUG() support" if EXPERT
1372         default y
1373         help
1374           Disabling this option eliminates support for BUG and WARN, reducing
1375           the size of your kernel image and potentially quietly ignoring
1376           numerous fatal conditions. You should only consider disabling this
1377           option for embedded systems with no facilities for reporting errors.
1378           Just say Y.
1379 
1380 config ELF_CORE
1381         depends on COREDUMP
1382         default y
1383         bool "Enable ELF core dumps" if EXPERT
1384         help
1385           Enable support for generating core dumps. Disabling saves about 4k.
1386 
1387 
1388 config PCSPKR_PLATFORM
1389         bool "Enable PC-Speaker support" if EXPERT
1390         depends on HAVE_PCSPKR_PLATFORM
1391         select I8253_LOCK
1392         default y
1393         help
1394           This option allows to disable the internal PC-Speaker
1395           support, saving some memory.
1396 
1397 config BASE_FULL
1398         default y
1399         bool "Enable full-sized data structures for core" if EXPERT
1400         help
1401           Disabling this option reduces the size of miscellaneous core
1402           kernel data structures. This saves memory on small machines,
1403           but may reduce performance.
1404 
1405 config FUTEX
1406         bool "Enable futex support" if EXPERT
1407         default y
1408         select RT_MUTEXES
1409         help
1410           Disabling this option will cause the kernel to be built without
1411           support for "fast userspace mutexes".  The resulting kernel may not
1412           run glibc-based applications correctly.
1413 
1414 config HAVE_FUTEX_CMPXCHG
1415         bool
1416         help
1417           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1418           is implemented and always working. This removes a couple of runtime
1419           checks.
1420 
1421 config EPOLL
1422         bool "Enable eventpoll support" if EXPERT
1423         default y
1424         select ANON_INODES
1425         help
1426           Disabling this option will cause the kernel to be built without
1427           support for epoll family of system calls.
1428 
1429 config SIGNALFD
1430         bool "Enable signalfd() system call" if EXPERT
1431         select ANON_INODES
1432         default y
1433         help
1434           Enable the signalfd() system call that allows to receive signals
1435           on a file descriptor.
1436 
1437           If unsure, say Y.
1438 
1439 config TIMERFD
1440         bool "Enable timerfd() system call" if EXPERT
1441         select ANON_INODES
1442         default y
1443         help
1444           Enable the timerfd() system call that allows to receive timer
1445           events on a file descriptor.
1446 
1447           If unsure, say Y.
1448 
1449 config EVENTFD
1450         bool "Enable eventfd() system call" if EXPERT
1451         select ANON_INODES
1452         default y
1453         help
1454           Enable the eventfd() system call that allows to receive both
1455           kernel notification (ie. KAIO) or userspace notifications.
1456 
1457           If unsure, say Y.
1458 
1459 config SHMEM
1460         bool "Use full shmem filesystem" if EXPERT
1461         default y
1462         depends on MMU
1463         help
1464           The shmem is an internal filesystem used to manage shared memory.
1465           It is backed by swap and manages resource limits. It is also exported
1466           to userspace as tmpfs if TMPFS is enabled. Disabling this
1467           option replaces shmem and tmpfs with the much simpler ramfs code,
1468           which may be appropriate on small systems without swap.
1469 
1470 config AIO
1471         bool "Enable AIO support" if EXPERT
1472         default y
1473         help
1474           This option enables POSIX asynchronous I/O which may by used
1475           by some high performance threaded applications. Disabling
1476           this option saves about 7k.
1477 
1478 config PCI_QUIRKS
1479         default y
1480         bool "Enable PCI quirk workarounds" if EXPERT
1481         depends on PCI
1482         help
1483           This enables workarounds for various PCI chipset
1484           bugs/quirks. Disable this only if your target machine is
1485           unaffected by PCI quirks.
1486 
1487 config EMBEDDED
1488         bool "Embedded system"
1489         option allnoconfig_y
1490         select EXPERT
1491         help
1492           This option should be enabled if compiling the kernel for
1493           an embedded system so certain expert options are available
1494           for configuration.
1495 
1496 config HAVE_PERF_EVENTS
1497         bool
1498         help
1499           See tools/perf/design.txt for details.
1500 
1501 config PERF_USE_VMALLOC
1502         bool
1503         help
1504           See tools/perf/design.txt for details
1505 
1506 menu "Kernel Performance Events And Counters"
1507 
1508 config PERF_EVENTS
1509         bool "Kernel performance events and counters"
1510         default y if PROFILING
1511         depends on HAVE_PERF_EVENTS
1512         select ANON_INODES
1513         select IRQ_WORK
1514         help
1515           Enable kernel support for various performance events provided
1516           by software and hardware.
1517 
1518           Software events are supported either built-in or via the
1519           use of generic tracepoints.
1520 
1521           Most modern CPUs support performance events via performance
1522           counter registers. These registers count the number of certain
1523           types of hw events: such as instructions executed, cachemisses
1524           suffered, or branches mis-predicted - without slowing down the
1525           kernel or applications. These registers can also trigger interrupts
1526           when a threshold number of events have passed - and can thus be
1527           used to profile the code that runs on that CPU.
1528 
1529           The Linux Performance Event subsystem provides an abstraction of
1530           these software and hardware event capabilities, available via a
1531           system call and used by the "perf" utility in tools/perf/. It
1532           provides per task and per CPU counters, and it provides event
1533           capabilities on top of those.
1534 
1535           Say Y if unsure.
1536 
1537 config DEBUG_PERF_USE_VMALLOC
1538         default n
1539         bool "Debug: use vmalloc to back perf mmap() buffers"
1540         depends on PERF_EVENTS && DEBUG_KERNEL
1541         select PERF_USE_VMALLOC
1542         help
1543          Use vmalloc memory to back perf mmap() buffers.
1544 
1545          Mostly useful for debugging the vmalloc code on platforms
1546          that don't require it.
1547 
1548          Say N if unsure.
1549 
1550 endmenu
1551 
1552 config VM_EVENT_COUNTERS
1553         default y
1554         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1555         help
1556           VM event counters are needed for event counts to be shown.
1557           This option allows the disabling of the VM event counters
1558           on EXPERT systems.  /proc/vmstat will only show page counts
1559           if VM event counters are disabled.
1560 
1561 config SLUB_DEBUG
1562         default y
1563         bool "Enable SLUB debugging support" if EXPERT
1564         depends on SLUB && SYSFS
1565         help
1566           SLUB has extensive debug support features. Disabling these can
1567           result in significant savings in code size. This also disables
1568           SLUB sysfs support. /sys/slab will not exist and there will be
1569           no support for cache validation etc.
1570 
1571 config COMPAT_BRK
1572         bool "Disable heap randomization"
1573         default y
1574         help
1575           Randomizing heap placement makes heap exploits harder, but it
1576           also breaks ancient binaries (including anything libc5 based).
1577           This option changes the bootup default to heap randomization
1578           disabled, and can be overridden at runtime by setting
1579           /proc/sys/kernel/randomize_va_space to 2.
1580 
1581           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1582 
1583 choice
1584         prompt "Choose SLAB allocator"
1585         default SLUB
1586         help
1587            This option allows to select a slab allocator.
1588 
1589 config SLAB
1590         bool "SLAB"
1591         help
1592           The regular slab allocator that is established and known to work
1593           well in all environments. It organizes cache hot objects in
1594           per cpu and per node queues.
1595 
1596 config SLUB
1597         bool "SLUB (Unqueued Allocator)"
1598         help
1599            SLUB is a slab allocator that minimizes cache line usage
1600            instead of managing queues of cached objects (SLAB approach).
1601            Per cpu caching is realized using slabs of objects instead
1602            of queues of objects. SLUB can use memory efficiently
1603            and has enhanced diagnostics. SLUB is the default choice for
1604            a slab allocator.
1605 
1606 config SLOB
1607         depends on EXPERT
1608         bool "SLOB (Simple Allocator)"
1609         help
1610            SLOB replaces the stock allocator with a drastically simpler
1611            allocator. SLOB is generally more space efficient but
1612            does not perform as well on large systems.
1613 
1614 endchoice
1615 
1616 config SLUB_CPU_PARTIAL
1617         default y
1618         depends on SLUB && SMP
1619         bool "SLUB per cpu partial cache"
1620         help
1621           Per cpu partial caches accellerate objects allocation and freeing
1622           that is local to a processor at the price of more indeterminism
1623           in the latency of the free. On overflow these caches will be cleared
1624           which requires the taking of locks that may cause latency spikes.
1625           Typically one would choose no for a realtime system.
1626 
1627 config MMAP_ALLOW_UNINITIALIZED
1628         bool "Allow mmapped anonymous memory to be uninitialized"
1629         depends on EXPERT && !MMU
1630         default n
1631         help
1632           Normally, and according to the Linux spec, anonymous memory obtained
1633           from mmap() has it's contents cleared before it is passed to
1634           userspace.  Enabling this config option allows you to request that
1635           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1636           providing a huge performance boost.  If this option is not enabled,
1637           then the flag will be ignored.
1638 
1639           This is taken advantage of by uClibc's malloc(), and also by
1640           ELF-FDPIC binfmt's brk and stack allocator.
1641 
1642           Because of the obvious security issues, this option should only be
1643           enabled on embedded devices where you control what is run in
1644           userspace.  Since that isn't generally a problem on no-MMU systems,
1645           it is normally safe to say Y here.
1646 
1647           See Documentation/nommu-mmap.txt for more information.
1648 
1649 config SYSTEM_TRUSTED_KEYRING
1650         bool "Provide system-wide ring of trusted keys"
1651         depends on KEYS
1652         help
1653           Provide a system keyring to which trusted keys can be added.  Keys in
1654           the keyring are considered to be trusted.  Keys may be added at will
1655           by the kernel from compiled-in data and from hardware key stores, but
1656           userspace may only add extra keys if those keys can be verified by
1657           keys already in the keyring.
1658 
1659           Keys in this keyring are used by module signature checking.
1660 
1661 config PROFILING
1662         bool "Profiling support"
1663         help
1664           Say Y here to enable the extended profiling support mechanisms used
1665           by profilers such as OProfile.
1666 
1667 #
1668 # Place an empty function call at each tracepoint site. Can be
1669 # dynamically changed for a probe function.
1670 #
1671 config TRACEPOINTS
1672         bool
1673 
1674 source "arch/Kconfig"
1675 
1676 endmenu         # General setup
1677 
1678 config HAVE_GENERIC_DMA_COHERENT
1679         bool
1680         default n
1681 
1682 config SLABINFO
1683         bool
1684         depends on PROC_FS
1685         depends on SLAB || SLUB_DEBUG
1686         default y
1687 
1688 config RT_MUTEXES
1689         boolean
1690 
1691 config BASE_SMALL
1692         int
1693         default 0 if BASE_FULL
1694         default 1 if !BASE_FULL
1695 
1696 menuconfig MODULES
1697         bool "Enable loadable module support"
1698         option modules
1699         help
1700           Kernel modules are small pieces of compiled code which can
1701           be inserted in the running kernel, rather than being
1702           permanently built into the kernel.  You use the "modprobe"
1703           tool to add (and sometimes remove) them.  If you say Y here,
1704           many parts of the kernel can be built as modules (by
1705           answering M instead of Y where indicated): this is most
1706           useful for infrequently used options which are not required
1707           for booting.  For more information, see the man pages for
1708           modprobe, lsmod, modinfo, insmod and rmmod.
1709 
1710           If you say Y here, you will need to run "make
1711           modules_install" to put the modules under /lib/modules/
1712           where modprobe can find them (you may need to be root to do
1713           this).
1714 
1715           If unsure, say Y.
1716 
1717 if MODULES
1718 
1719 config MODULE_FORCE_LOAD
1720         bool "Forced module loading"
1721         default n
1722         help
1723           Allow loading of modules without version information (ie. modprobe
1724           --force).  Forced module loading sets the 'F' (forced) taint flag and
1725           is usually a really bad idea.
1726 
1727 config MODULE_UNLOAD
1728         bool "Module unloading"
1729         help
1730           Without this option you will not be able to unload any
1731           modules (note that some modules may not be unloadable
1732           anyway), which makes your kernel smaller, faster
1733           and simpler.  If unsure, say Y.
1734 
1735 config MODULE_FORCE_UNLOAD
1736         bool "Forced module unloading"
1737         depends on MODULE_UNLOAD
1738         help
1739           This option allows you to force a module to unload, even if the
1740           kernel believes it is unsafe: the kernel will remove the module
1741           without waiting for anyone to stop using it (using the -f option to
1742           rmmod).  This is mainly for kernel developers and desperate users.
1743           If unsure, say N.
1744 
1745 config MODVERSIONS
1746         bool "Module versioning support"
1747         help
1748           Usually, you have to use modules compiled with your kernel.
1749           Saying Y here makes it sometimes possible to use modules
1750           compiled for different kernels, by adding enough information
1751           to the modules to (hopefully) spot any changes which would
1752           make them incompatible with the kernel you are running.  If
1753           unsure, say N.
1754 
1755 config MODULE_SRCVERSION_ALL
1756         bool "Source checksum for all modules"
1757         help
1758           Modules which contain a MODULE_VERSION get an extra "srcversion"
1759           field inserted into their modinfo section, which contains a
1760           sum of the source files which made it.  This helps maintainers
1761           see exactly which source was used to build a module (since
1762           others sometimes change the module source without updating
1763           the version).  With this option, such a "srcversion" field
1764           will be created for all modules.  If unsure, say N.
1765 
1766 config MODULE_SIG
1767         bool "Module signature verification"
1768         depends on MODULES
1769         select SYSTEM_TRUSTED_KEYRING
1770         select KEYS
1771         select CRYPTO
1772         select ASYMMETRIC_KEY_TYPE
1773         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1774         select PUBLIC_KEY_ALGO_RSA
1775         select ASN1
1776         select OID_REGISTRY
1777         select X509_CERTIFICATE_PARSER
1778         help
1779           Check modules for valid signatures upon load: the signature
1780           is simply appended to the module. For more information see
1781           Documentation/module-signing.txt.
1782 
1783           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1784           module DOES NOT get stripped after being signed.  This includes the
1785           debuginfo strip done by some packagers (such as rpmbuild) and
1786           inclusion into an initramfs that wants the module size reduced.
1787 
1788 config MODULE_SIG_FORCE
1789         bool "Require modules to be validly signed"
1790         depends on MODULE_SIG
1791         help
1792           Reject unsigned modules or signed modules for which we don't have a
1793           key.  Without this, such modules will simply taint the kernel.
1794 
1795 config MODULE_SIG_ALL
1796         bool "Automatically sign all modules"
1797         default y
1798         depends on MODULE_SIG
1799         help
1800           Sign all modules during make modules_install. Without this option,
1801           modules must be signed manually, using the scripts/sign-file tool.
1802 
1803 comment "Do not forget to sign required modules with scripts/sign-file"
1804         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1805 
1806 choice
1807         prompt "Which hash algorithm should modules be signed with?"
1808         depends on MODULE_SIG
1809         help
1810           This determines which sort of hashing algorithm will be used during
1811           signature generation.  This algorithm _must_ be built into the kernel
1812           directly so that signature verification can take place.  It is not
1813           possible to load a signed module containing the algorithm to check
1814           the signature on that module.
1815 
1816 config MODULE_SIG_SHA1
1817         bool "Sign modules with SHA-1"
1818         select CRYPTO_SHA1
1819 
1820 config MODULE_SIG_SHA224
1821         bool "Sign modules with SHA-224"
1822         select CRYPTO_SHA256
1823 
1824 config MODULE_SIG_SHA256
1825         bool "Sign modules with SHA-256"
1826         select CRYPTO_SHA256
1827 
1828 config MODULE_SIG_SHA384
1829         bool "Sign modules with SHA-384"
1830         select CRYPTO_SHA512
1831 
1832 config MODULE_SIG_SHA512
1833         bool "Sign modules with SHA-512"
1834         select CRYPTO_SHA512
1835 
1836 endchoice
1837 
1838 config MODULE_SIG_HASH
1839         string
1840         depends on MODULE_SIG
1841         default "sha1" if MODULE_SIG_SHA1
1842         default "sha224" if MODULE_SIG_SHA224
1843         default "sha256" if MODULE_SIG_SHA256
1844         default "sha384" if MODULE_SIG_SHA384
1845         default "sha512" if MODULE_SIG_SHA512
1846 
1847 endif # MODULES
1848 
1849 config INIT_ALL_POSSIBLE
1850         bool
1851         help
1852           Back when each arch used to define their own cpu_online_mask and
1853           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1854           with all 1s, and others with all 0s.  When they were centralised,
1855           it was better to provide this option than to break all the archs
1856           and have several arch maintainers pursuing me down dark alleys.
1857 
1858 config STOP_MACHINE
1859         bool
1860         default y
1861         depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1862         help
1863           Need stop_machine() primitive.
1864 
1865 source "block/Kconfig"
1866 
1867 config PREEMPT_NOTIFIERS
1868         bool
1869 
1870 config PADATA
1871         depends on SMP
1872         bool
1873 
1874 # Can be selected by architectures with broken toolchains
1875 # that get confused by correct const<->read_only section
1876 # mappings
1877 config BROKEN_RODATA
1878         bool
1879 
1880 config ASN1
1881         tristate
1882         help
1883           Build a simple ASN.1 grammar compiler that produces a bytecode output
1884           that can be interpreted by the ASN.1 stream decoder and used to
1885           inform it as to what tags are to be expected in a stream and what
1886           functions to call on what tags.
1887 
1888 source "kernel/Kconfig.locks"

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