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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 AUDIT
277         bool "Auditing support"
278         depends on NET
279         help
280           Enable auditing infrastructure that can be used with another
281           kernel subsystem, such as SELinux (which requires this for
282           logging of avc messages output).  Does not do system-call
283           auditing without CONFIG_AUDITSYSCALL.
284 
285 config AUDITSYSCALL
286         bool "Enable system-call auditing support"
287         depends on AUDIT && (X86 || PARISC || PPC || S390 || IA64 || UML || SPARC64 || SUPERH || (ARM && AEABI && !OABI_COMPAT) || ALPHA)
288         default y if SECURITY_SELINUX
289         help
290           Enable low-overhead system-call auditing infrastructure that
291           can be used independently or with another kernel subsystem,
292           such as SELinux.
293 
294 config AUDIT_WATCH
295         def_bool y
296         depends on AUDITSYSCALL
297         select FSNOTIFY
298 
299 config AUDIT_TREE
300         def_bool y
301         depends on AUDITSYSCALL
302         select FSNOTIFY
303 
304 source "kernel/irq/Kconfig"
305 source "kernel/time/Kconfig"
306 
307 menu "CPU/Task time and stats accounting"
308 
309 config VIRT_CPU_ACCOUNTING
310         bool
311 
312 choice
313         prompt "Cputime accounting"
314         default TICK_CPU_ACCOUNTING if !PPC64
315         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
316 
317 # Kind of a stub config for the pure tick based cputime accounting
318 config TICK_CPU_ACCOUNTING
319         bool "Simple tick based cputime accounting"
320         depends on !S390 && !NO_HZ_FULL
321         help
322           This is the basic tick based cputime accounting that maintains
323           statistics about user, system and idle time spent on per jiffies
324           granularity.
325 
326           If unsure, say Y.
327 
328 config VIRT_CPU_ACCOUNTING_NATIVE
329         bool "Deterministic task and CPU time accounting"
330         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
331         select VIRT_CPU_ACCOUNTING
332         help
333           Select this option to enable more accurate task and CPU time
334           accounting.  This is done by reading a CPU counter on each
335           kernel entry and exit and on transitions within the kernel
336           between system, softirq and hardirq state, so there is a
337           small performance impact.  In the case of s390 or IBM POWER > 5,
338           this also enables accounting of stolen time on logically-partitioned
339           systems.
340 
341 config VIRT_CPU_ACCOUNTING_GEN
342         bool "Full dynticks CPU time accounting"
343         depends on HAVE_CONTEXT_TRACKING
344         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
345         select VIRT_CPU_ACCOUNTING
346         select CONTEXT_TRACKING
347         help
348           Select this option to enable task and CPU time accounting on full
349           dynticks systems. This accounting is implemented by watching every
350           kernel-user boundaries using the context tracking subsystem.
351           The accounting is thus performed at the expense of some significant
352           overhead.
353 
354           For now this is only useful if you are working on the full
355           dynticks subsystem development.
356 
357           If unsure, say N.
358 
359 config IRQ_TIME_ACCOUNTING
360         bool "Fine granularity task level IRQ time accounting"
361         depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
362         help
363           Select this option to enable fine granularity task irq time
364           accounting. This is done by reading a timestamp on each
365           transitions between softirq and hardirq state, so there can be a
366           small performance impact.
367 
368           If in doubt, say N here.
369 
370 endchoice
371 
372 config BSD_PROCESS_ACCT
373         bool "BSD Process Accounting"
374         help
375           If you say Y here, a user level program will be able to instruct the
376           kernel (via a special system call) to write process accounting
377           information to a file: whenever a process exits, information about
378           that process will be appended to the file by the kernel.  The
379           information includes things such as creation time, owning user,
380           command name, memory usage, controlling terminal etc. (the complete
381           list is in the struct acct in <file:include/linux/acct.h>).  It is
382           up to the user level program to do useful things with this
383           information.  This is generally a good idea, so say Y.
384 
385 config BSD_PROCESS_ACCT_V3
386         bool "BSD Process Accounting version 3 file format"
387         depends on BSD_PROCESS_ACCT
388         default n
389         help
390           If you say Y here, the process accounting information is written
391           in a new file format that also logs the process IDs of each
392           process and it's parent. Note that this file format is incompatible
393           with previous v0/v1/v2 file formats, so you will need updated tools
394           for processing it. A preliminary version of these tools is available
395           at <http://www.gnu.org/software/acct/>.
396 
397 config TASKSTATS
398         bool "Export task/process statistics through netlink"
399         depends on NET
400         default n
401         help
402           Export selected statistics for tasks/processes through the
403           generic netlink interface. Unlike BSD process accounting, the
404           statistics are available during the lifetime of tasks/processes as
405           responses to commands. Like BSD accounting, they are sent to user
406           space on task exit.
407 
408           Say N if unsure.
409 
410 config TASK_DELAY_ACCT
411         bool "Enable per-task delay accounting"
412         depends on TASKSTATS
413         help
414           Collect information on time spent by a task waiting for system
415           resources like cpu, synchronous block I/O completion and swapping
416           in pages. Such statistics can help in setting a task's priorities
417           relative to other tasks for cpu, io, rss limits etc.
418 
419           Say N if unsure.
420 
421 config TASK_XACCT
422         bool "Enable extended accounting over taskstats"
423         depends on TASKSTATS
424         help
425           Collect extended task accounting data and send the data
426           to userland for processing over the taskstats interface.
427 
428           Say N if unsure.
429 
430 config TASK_IO_ACCOUNTING
431         bool "Enable per-task storage I/O accounting"
432         depends on TASK_XACCT
433         help
434           Collect information on the number of bytes of storage I/O which this
435           task has caused.
436 
437           Say N if unsure.
438 
439 endmenu # "CPU/Task time and stats accounting"
440 
441 menu "RCU Subsystem"
442 
443 choice
444         prompt "RCU Implementation"
445         default TREE_RCU
446 
447 config TREE_RCU
448         bool "Tree-based hierarchical RCU"
449         depends on !PREEMPT && SMP
450         select IRQ_WORK
451         help
452           This option selects the RCU implementation that is
453           designed for very large SMP system with hundreds or
454           thousands of CPUs.  It also scales down nicely to
455           smaller systems.
456 
457 config TREE_PREEMPT_RCU
458         bool "Preemptible tree-based hierarchical RCU"
459         depends on PREEMPT
460         select IRQ_WORK
461         help
462           This option selects the RCU implementation that is
463           designed for very large SMP systems with hundreds or
464           thousands of CPUs, but for which real-time response
465           is also required.  It also scales down nicely to
466           smaller systems.
467 
468           Select this option if you are unsure.
469 
470 config TINY_RCU
471         bool "UP-only small-memory-footprint RCU"
472         depends on !PREEMPT && !SMP
473         help
474           This option selects the RCU implementation that is
475           designed for UP systems from which real-time response
476           is not required.  This option greatly reduces the
477           memory footprint of RCU.
478 
479 endchoice
480 
481 config PREEMPT_RCU
482         def_bool TREE_PREEMPT_RCU
483         help
484           This option enables preemptible-RCU code that is common between
485           the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
486 
487 config RCU_STALL_COMMON
488         def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
489         help
490           This option enables RCU CPU stall code that is common between
491           the TINY and TREE variants of RCU.  The purpose is to allow
492           the tiny variants to disable RCU CPU stall warnings, while
493           making these warnings mandatory for the tree variants.
494 
495 config CONTEXT_TRACKING
496        bool
497 
498 config RCU_USER_QS
499         bool "Consider userspace as in RCU extended quiescent state"
500         depends on HAVE_CONTEXT_TRACKING && SMP
501         select CONTEXT_TRACKING
502         help
503           This option sets hooks on kernel / userspace boundaries and
504           puts RCU in extended quiescent state when the CPU runs in
505           userspace. It means that when a CPU runs in userspace, it is
506           excluded from the global RCU state machine and thus doesn't
507           try to keep the timer tick on for RCU.
508 
509           Unless you want to hack and help the development of the full
510           dynticks mode, you shouldn't enable this option.  It also
511           adds unnecessary overhead.
512 
513           If unsure say N
514 
515 config CONTEXT_TRACKING_FORCE
516         bool "Force context tracking"
517         depends on CONTEXT_TRACKING
518         default y if !NO_HZ_FULL
519         help
520           The major pre-requirement for full dynticks to work is to
521           support the context tracking subsystem. But there are also
522           other dependencies to provide in order to make the full
523           dynticks working.
524 
525           This option stands for testing when an arch implements the
526           context tracking backend but doesn't yet fullfill all the
527           requirements to make the full dynticks feature working.
528           Without the full dynticks, there is no way to test the support
529           for context tracking and the subsystems that rely on it: RCU
530           userspace extended quiescent state and tickless cputime
531           accounting. This option copes with the absence of the full
532           dynticks subsystem by forcing the context tracking on all
533           CPUs in the system.
534 
535           Say Y only if you're working on the development of an
536           architecture backend for the context tracking.
537 
538           Say N otherwise, this option brings an overhead that you
539           don't want in production.
540 
541 
542 config RCU_FANOUT
543         int "Tree-based hierarchical RCU fanout value"
544         range 2 64 if 64BIT
545         range 2 32 if !64BIT
546         depends on TREE_RCU || TREE_PREEMPT_RCU
547         default 64 if 64BIT
548         default 32 if !64BIT
549         help
550           This option controls the fanout of hierarchical implementations
551           of RCU, allowing RCU to work efficiently on machines with
552           large numbers of CPUs.  This value must be at least the fourth
553           root of NR_CPUS, which allows NR_CPUS to be insanely large.
554           The default value of RCU_FANOUT should be used for production
555           systems, but if you are stress-testing the RCU implementation
556           itself, small RCU_FANOUT values allow you to test large-system
557           code paths on small(er) systems.
558 
559           Select a specific number if testing RCU itself.
560           Take the default if unsure.
561 
562 config RCU_FANOUT_LEAF
563         int "Tree-based hierarchical RCU leaf-level fanout value"
564         range 2 RCU_FANOUT if 64BIT
565         range 2 RCU_FANOUT if !64BIT
566         depends on TREE_RCU || TREE_PREEMPT_RCU
567         default 16
568         help
569           This option controls the leaf-level fanout of hierarchical
570           implementations of RCU, and allows trading off cache misses
571           against lock contention.  Systems that synchronize their
572           scheduling-clock interrupts for energy-efficiency reasons will
573           want the default because the smaller leaf-level fanout keeps
574           lock contention levels acceptably low.  Very large systems
575           (hundreds or thousands of CPUs) will instead want to set this
576           value to the maximum value possible in order to reduce the
577           number of cache misses incurred during RCU's grace-period
578           initialization.  These systems tend to run CPU-bound, and thus
579           are not helped by synchronized interrupts, and thus tend to
580           skew them, which reduces lock contention enough that large
581           leaf-level fanouts work well.
582 
583           Select a specific number if testing RCU itself.
584 
585           Select the maximum permissible value for large systems.
586 
587           Take the default if unsure.
588 
589 config RCU_FANOUT_EXACT
590         bool "Disable tree-based hierarchical RCU auto-balancing"
591         depends on TREE_RCU || TREE_PREEMPT_RCU
592         default n
593         help
594           This option forces use of the exact RCU_FANOUT value specified,
595           regardless of imbalances in the hierarchy.  This is useful for
596           testing RCU itself, and might one day be useful on systems with
597           strong NUMA behavior.
598 
599           Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
600 
601           Say N if unsure.
602 
603 config RCU_FAST_NO_HZ
604         bool "Accelerate last non-dyntick-idle CPU's grace periods"
605         depends on NO_HZ_COMMON && SMP
606         default n
607         help
608           This option permits CPUs to enter dynticks-idle state even if
609           they have RCU callbacks queued, and prevents RCU from waking
610           these CPUs up more than roughly once every four jiffies (by
611           default, you can adjust this using the rcutree.rcu_idle_gp_delay
612           parameter), thus improving energy efficiency.  On the other
613           hand, this option increases the duration of RCU grace periods,
614           for example, slowing down synchronize_rcu().
615 
616           Say Y if energy efficiency is critically important, and you
617                 don't care about increased grace-period durations.
618 
619           Say N if you are unsure.
620 
621 config TREE_RCU_TRACE
622         def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
623         select DEBUG_FS
624         help
625           This option provides tracing for the TREE_RCU and
626           TREE_PREEMPT_RCU implementations, permitting Makefile to
627           trivially select kernel/rcutree_trace.c.
628 
629 config RCU_BOOST
630         bool "Enable RCU priority boosting"
631         depends on RT_MUTEXES && PREEMPT_RCU
632         default n
633         help
634           This option boosts the priority of preempted RCU readers that
635           block the current preemptible RCU grace period for too long.
636           This option also prevents heavy loads from blocking RCU
637           callback invocation for all flavors of RCU.
638 
639           Say Y here if you are working with real-time apps or heavy loads
640           Say N here if you are unsure.
641 
642 config RCU_BOOST_PRIO
643         int "Real-time priority to boost RCU readers to"
644         range 1 99
645         depends on RCU_BOOST
646         default 1
647         help
648           This option specifies the real-time priority to which long-term
649           preempted RCU readers are to be boosted.  If you are working
650           with a real-time application that has one or more CPU-bound
651           threads running at a real-time priority level, you should set
652           RCU_BOOST_PRIO to a priority higher then the highest-priority
653           real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
654           of 1 is appropriate in the common case, which is real-time
655           applications that do not have any CPU-bound threads.
656 
657           Some real-time applications might not have a single real-time
658           thread that saturates a given CPU, but instead might have
659           multiple real-time threads that, taken together, fully utilize
660           that CPU.  In this case, you should set RCU_BOOST_PRIO to
661           a priority higher than the lowest-priority thread that is
662           conspiring to prevent the CPU from running any non-real-time
663           tasks.  For example, if one thread at priority 10 and another
664           thread at priority 5 are between themselves fully consuming
665           the CPU time on a given CPU, then RCU_BOOST_PRIO should be
666           set to priority 6 or higher.
667 
668           Specify the real-time priority, or take the default if unsure.
669 
670 config RCU_BOOST_DELAY
671         int "Milliseconds to delay boosting after RCU grace-period start"
672         range 0 3000
673         depends on RCU_BOOST
674         default 500
675         help
676           This option specifies the time to wait after the beginning of
677           a given grace period before priority-boosting preempted RCU
678           readers blocking that grace period.  Note that any RCU reader
679           blocking an expedited RCU grace period is boosted immediately.
680 
681           Accept the default if unsure.
682 
683 config RCU_NOCB_CPU
684         bool "Offload RCU callback processing from boot-selected CPUs"
685         depends on TREE_RCU || TREE_PREEMPT_RCU
686         default n
687         help
688           Use this option to reduce OS jitter for aggressive HPC or
689           real-time workloads.  It can also be used to offload RCU
690           callback invocation to energy-efficient CPUs in battery-powered
691           asymmetric multiprocessors.
692 
693           This option offloads callback invocation from the set of
694           CPUs specified at boot time by the rcu_nocbs parameter.
695           For each such CPU, a kthread ("rcuox/N") will be created to
696           invoke callbacks, where the "N" is the CPU being offloaded,
697           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
698           "s" for RCU-sched.  Nothing prevents this kthread from running
699           on the specified CPUs, but (1) the kthreads may be preempted
700           between each callback, and (2) affinity or cgroups can be used
701           to force the kthreads to run on whatever set of CPUs is desired.
702 
703           Say Y here if you want to help to debug reduced OS jitter.
704           Say N here if you are unsure.
705 
706 choice
707         prompt "Build-forced no-CBs CPUs"
708         default RCU_NOCB_CPU_NONE
709         help
710           This option allows no-CBs CPUs (whose RCU callbacks are invoked
711           from kthreads rather than from softirq context) to be specified
712           at build time.  Additional no-CBs CPUs may be specified by
713           the rcu_nocbs= boot parameter.
714 
715 config RCU_NOCB_CPU_NONE
716         bool "No build_forced no-CBs CPUs"
717         depends on RCU_NOCB_CPU && !NO_HZ_FULL
718         help
719           This option does not force any of the CPUs to be no-CBs CPUs.
720           Only CPUs designated by the rcu_nocbs= boot parameter will be
721           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
722           kthreads whose names begin with "rcuo".  All other CPUs will
723           invoke their own RCU callbacks in softirq context.
724 
725           Select this option if you want to choose no-CBs CPUs at
726           boot time, for example, to allow testing of different no-CBs
727           configurations without having to rebuild the kernel each time.
728 
729 config RCU_NOCB_CPU_ZERO
730         bool "CPU 0 is a build_forced no-CBs CPU"
731         depends on RCU_NOCB_CPU && !NO_HZ_FULL
732         help
733           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
734           callbacks are invoked by a per-CPU kthread whose name begins
735           with "rcuo".  Additional CPUs may be designated as no-CBs
736           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
737           All other CPUs will invoke their own RCU callbacks in softirq
738           context.
739 
740           Select this if CPU 0 needs to be a no-CBs CPU for real-time
741           or energy-efficiency reasons, but the real reason it exists
742           is to ensure that randconfig testing covers mixed systems.
743 
744 config RCU_NOCB_CPU_ALL
745         bool "All CPUs are build_forced no-CBs CPUs"
746         depends on RCU_NOCB_CPU
747         help
748           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
749           boot parameter will be ignored.  All CPUs' RCU callbacks will
750           be executed in the context of per-CPU rcuo kthreads created for
751           this purpose.  Assuming that the kthreads whose names start with
752           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
753           on the remaining CPUs, but might decrease memory locality during
754           RCU-callback invocation, thus potentially degrading throughput.
755 
756           Select this if all CPUs need to be no-CBs CPUs for real-time
757           or energy-efficiency reasons.
758 
759 endchoice
760 
761 endmenu # "RCU Subsystem"
762 
763 config IKCONFIG
764         tristate "Kernel .config support"
765         ---help---
766           This option enables the complete Linux kernel ".config" file
767           contents to be saved in the kernel. It provides documentation
768           of which kernel options are used in a running kernel or in an
769           on-disk kernel.  This information can be extracted from the kernel
770           image file with the script scripts/extract-ikconfig and used as
771           input to rebuild the current kernel or to build another kernel.
772           It can also be extracted from a running kernel by reading
773           /proc/config.gz if enabled (below).
774 
775 config IKCONFIG_PROC
776         bool "Enable access to .config through /proc/config.gz"
777         depends on IKCONFIG && PROC_FS
778         ---help---
779           This option enables access to the kernel configuration file
780           through /proc/config.gz.
781 
782 config LOG_BUF_SHIFT
783         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
784         range 12 21
785         default 17
786         help
787           Select kernel log buffer size as a power of 2.
788           Examples:
789                      17 => 128 KB
790                      16 => 64 KB
791                      15 => 32 KB
792                      14 => 16 KB
793                      13 =>  8 KB
794                      12 =>  4 KB
795 
796 #
797 # Architectures with an unreliable sched_clock() should select this:
798 #
799 config HAVE_UNSTABLE_SCHED_CLOCK
800         bool
801 
802 config GENERIC_SCHED_CLOCK
803         bool
804 
805 #
806 # For architectures that want to enable the support for NUMA-affine scheduler
807 # balancing logic:
808 #
809 config ARCH_SUPPORTS_NUMA_BALANCING
810         bool
811 
812 #
813 # For architectures that know their GCC __int128 support is sound
814 #
815 config ARCH_SUPPORTS_INT128
816         bool
817 
818 # For architectures that (ab)use NUMA to represent different memory regions
819 # all cpu-local but of different latencies, such as SuperH.
820 #
821 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
822         bool
823 
824 #
825 # For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
826 config ARCH_WANTS_PROT_NUMA_PROT_NONE
827         bool
828 
829 config ARCH_USES_NUMA_PROT_NONE
830         bool
831         default y
832         depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
833         depends on NUMA_BALANCING
834 
835 config NUMA_BALANCING_DEFAULT_ENABLED
836         bool "Automatically enable NUMA aware memory/task placement"
837         default y
838         depends on NUMA_BALANCING
839         help
840           If set, automatic NUMA balancing will be enabled if running on a NUMA
841           machine.
842 
843 config NUMA_BALANCING
844         bool "Memory placement aware NUMA scheduler"
845         depends on ARCH_SUPPORTS_NUMA_BALANCING
846         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
847         depends on SMP && NUMA && MIGRATION
848         help
849           This option adds support for automatic NUMA aware memory/task placement.
850           The mechanism is quite primitive and is based on migrating memory when
851           it has references to the node the task is running on.
852 
853           This system will be inactive on UMA systems.
854 
855 menuconfig CGROUPS
856         boolean "Control Group support"
857         help
858           This option adds support for grouping sets of processes together, for
859           use with process control subsystems such as Cpusets, CFS, memory
860           controls or device isolation.
861           See
862                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
863                 - Documentation/cgroups/ (features for grouping, isolation
864                                           and resource control)
865 
866           Say N if unsure.
867 
868 if CGROUPS
869 
870 config CGROUP_DEBUG
871         bool "Example debug cgroup subsystem"
872         default n
873         help
874           This option enables a simple cgroup subsystem that
875           exports useful debugging information about the cgroups
876           framework.
877 
878           Say N if unsure.
879 
880 config CGROUP_FREEZER
881         bool "Freezer cgroup subsystem"
882         help
883           Provides a way to freeze and unfreeze all tasks in a
884           cgroup.
885 
886 config CGROUP_DEVICE
887         bool "Device controller for cgroups"
888         help
889           Provides a cgroup implementing whitelists for devices which
890           a process in the cgroup can mknod or open.
891 
892 config CPUSETS
893         bool "Cpuset support"
894         help
895           This option will let you create and manage CPUSETs which
896           allow dynamically partitioning a system into sets of CPUs and
897           Memory Nodes and assigning tasks to run only within those sets.
898           This is primarily useful on large SMP or NUMA systems.
899 
900           Say N if unsure.
901 
902 config PROC_PID_CPUSET
903         bool "Include legacy /proc/<pid>/cpuset file"
904         depends on CPUSETS
905         default y
906 
907 config CGROUP_CPUACCT
908         bool "Simple CPU accounting cgroup subsystem"
909         help
910           Provides a simple Resource Controller for monitoring the
911           total CPU consumed by the tasks in a cgroup.
912 
913 config RESOURCE_COUNTERS
914         bool "Resource counters"
915         help
916           This option enables controller independent resource accounting
917           infrastructure that works with cgroups.
918 
919 config MEMCG
920         bool "Memory Resource Controller for Control Groups"
921         depends on RESOURCE_COUNTERS
922         select MM_OWNER
923         select EVENTFD
924         help
925           Provides a memory resource controller that manages both anonymous
926           memory and page cache. (See Documentation/cgroups/memory.txt)
927 
928           Note that setting this option increases fixed memory overhead
929           associated with each page of memory in the system. By this,
930           8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
931           usage tracking struct at boot. Total amount of this is printed out
932           at boot.
933 
934           Only enable when you're ok with these trade offs and really
935           sure you need the memory resource controller. Even when you enable
936           this, you can set "cgroup_disable=memory" at your boot option to
937           disable memory resource controller and you can avoid overheads.
938           (and lose benefits of memory resource controller)
939 
940           This config option also selects MM_OWNER config option, which
941           could in turn add some fork/exit overhead.
942 
943 config MEMCG_SWAP
944         bool "Memory Resource Controller Swap Extension"
945         depends on MEMCG && SWAP
946         help
947           Add swap management feature to memory resource controller. When you
948           enable this, you can limit mem+swap usage per cgroup. In other words,
949           when you disable this, memory resource controller has no cares to
950           usage of swap...a process can exhaust all of the swap. This extension
951           is useful when you want to avoid exhaustion swap but this itself
952           adds more overheads and consumes memory for remembering information.
953           Especially if you use 32bit system or small memory system, please
954           be careful about enabling this. When memory resource controller
955           is disabled by boot option, this will be automatically disabled and
956           there will be no overhead from this. Even when you set this config=y,
957           if boot option "swapaccount=0" is set, swap will not be accounted.
958           Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
959           size is 4096bytes, 512k per 1Gbytes of swap.
960 config MEMCG_SWAP_ENABLED
961         bool "Memory Resource Controller Swap Extension enabled by default"
962         depends on MEMCG_SWAP
963         default y
964         help
965           Memory Resource Controller Swap Extension comes with its price in
966           a bigger memory consumption. General purpose distribution kernels
967           which want to enable the feature but keep it disabled by default
968           and let the user enable it by swapaccount=1 boot command line
969           parameter should have this option unselected.
970           For those who want to have the feature enabled by default should
971           select this option (if, for some reason, they need to disable it
972           then swapaccount=0 does the trick).
973 config MEMCG_KMEM
974         bool "Memory Resource Controller Kernel Memory accounting"
975         depends on MEMCG
976         depends on SLUB || SLAB
977         help
978           The Kernel Memory extension for Memory Resource Controller can limit
979           the amount of memory used by kernel objects in the system. Those are
980           fundamentally different from the entities handled by the standard
981           Memory Controller, which are page-based, and can be swapped. Users of
982           the kmem extension can use it to guarantee that no group of processes
983           will ever exhaust kernel resources alone.
984 
985 config CGROUP_HUGETLB
986         bool "HugeTLB Resource Controller for Control Groups"
987         depends on RESOURCE_COUNTERS && HUGETLB_PAGE
988         default n
989         help
990           Provides a cgroup Resource Controller for HugeTLB pages.
991           When you enable this, you can put a per cgroup limit on HugeTLB usage.
992           The limit is enforced during page fault. Since HugeTLB doesn't
993           support page reclaim, enforcing the limit at page fault time implies
994           that, the application will get SIGBUS signal if it tries to access
995           HugeTLB pages beyond its limit. This requires the application to know
996           beforehand how much HugeTLB pages it would require for its use. The
997           control group is tracked in the third page lru pointer. This means
998           that we cannot use the controller with huge page less than 3 pages.
999 
1000 config CGROUP_PERF
1001         bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1002         depends on PERF_EVENTS && CGROUPS
1003         help
1004           This option extends the per-cpu mode to restrict monitoring to
1005           threads which belong to the cgroup specified and run on the
1006           designated cpu.
1007 
1008           Say N if unsure.
1009 
1010 menuconfig CGROUP_SCHED
1011         bool "Group CPU scheduler"
1012         default n
1013         help
1014           This feature lets CPU scheduler recognize task groups and control CPU
1015           bandwidth allocation to such task groups. It uses cgroups to group
1016           tasks.
1017 
1018 if CGROUP_SCHED
1019 config FAIR_GROUP_SCHED
1020         bool "Group scheduling for SCHED_OTHER"
1021         depends on CGROUP_SCHED
1022         default CGROUP_SCHED
1023 
1024 config CFS_BANDWIDTH
1025         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1026         depends on FAIR_GROUP_SCHED
1027         default n
1028         help
1029           This option allows users to define CPU bandwidth rates (limits) for
1030           tasks running within the fair group scheduler.  Groups with no limit
1031           set are considered to be unconstrained and will run with no
1032           restriction.
1033           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1034 
1035 config RT_GROUP_SCHED
1036         bool "Group scheduling for SCHED_RR/FIFO"
1037         depends on CGROUP_SCHED
1038         default n
1039         help
1040           This feature lets you explicitly allocate real CPU bandwidth
1041           to task groups. If enabled, it will also make it impossible to
1042           schedule realtime tasks for non-root users until you allocate
1043           realtime bandwidth for them.
1044           See Documentation/scheduler/sched-rt-group.txt for more information.
1045 
1046 endif #CGROUP_SCHED
1047 
1048 config BLK_CGROUP
1049         bool "Block IO controller"
1050         depends on BLOCK
1051         default n
1052         ---help---
1053         Generic block IO controller cgroup interface. This is the common
1054         cgroup interface which should be used by various IO controlling
1055         policies.
1056 
1057         Currently, CFQ IO scheduler uses it to recognize task groups and
1058         control disk bandwidth allocation (proportional time slice allocation)
1059         to such task groups. It is also used by bio throttling logic in
1060         block layer to implement upper limit in IO rates on a device.
1061 
1062         This option only enables generic Block IO controller infrastructure.
1063         One needs to also enable actual IO controlling logic/policy. For
1064         enabling proportional weight division of disk bandwidth in CFQ, set
1065         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1066         CONFIG_BLK_DEV_THROTTLING=y.
1067 
1068         See Documentation/cgroups/blkio-controller.txt for more information.
1069 
1070 config DEBUG_BLK_CGROUP
1071         bool "Enable Block IO controller debugging"
1072         depends on BLK_CGROUP
1073         default n
1074         ---help---
1075         Enable some debugging help. Currently it exports additional stat
1076         files in a cgroup which can be useful for debugging.
1077 
1078 endif # CGROUPS
1079 
1080 config CHECKPOINT_RESTORE
1081         bool "Checkpoint/restore support" if EXPERT
1082         default n
1083         help
1084           Enables additional kernel features in a sake of checkpoint/restore.
1085           In particular it adds auxiliary prctl codes to setup process text,
1086           data and heap segment sizes, and a few additional /proc filesystem
1087           entries.
1088 
1089           If unsure, say N here.
1090 
1091 menuconfig NAMESPACES
1092         bool "Namespaces support" if EXPERT
1093         default !EXPERT
1094         help
1095           Provides the way to make tasks work with different objects using
1096           the same id. For example same IPC id may refer to different objects
1097           or same user id or pid may refer to different tasks when used in
1098           different namespaces.
1099 
1100 if NAMESPACES
1101 
1102 config UTS_NS
1103         bool "UTS namespace"
1104         default y
1105         help
1106           In this namespace tasks see different info provided with the
1107           uname() system call
1108 
1109 config IPC_NS
1110         bool "IPC namespace"
1111         depends on (SYSVIPC || POSIX_MQUEUE)
1112         default y
1113         help
1114           In this namespace tasks work with IPC ids which correspond to
1115           different IPC objects in different namespaces.
1116 
1117 config USER_NS
1118         bool "User namespace"
1119         default n
1120         help
1121           This allows containers, i.e. vservers, to use user namespaces
1122           to provide different user info for different servers.
1123 
1124           When user namespaces are enabled in the kernel it is
1125           recommended that the MEMCG and MEMCG_KMEM options also be
1126           enabled and that user-space use the memory control groups to
1127           limit the amount of memory a memory unprivileged users can
1128           use.
1129 
1130           If unsure, say N.
1131 
1132 config PID_NS
1133         bool "PID Namespaces"
1134         default y
1135         help
1136           Support process id namespaces.  This allows having multiple
1137           processes with the same pid as long as they are in different
1138           pid namespaces.  This is a building block of containers.
1139 
1140 config NET_NS
1141         bool "Network namespace"
1142         depends on NET
1143         default y
1144         help
1145           Allow user space to create what appear to be multiple instances
1146           of the network stack.
1147 
1148 endif # NAMESPACES
1149 
1150 config SCHED_AUTOGROUP
1151         bool "Automatic process group scheduling"
1152         select CGROUPS
1153         select CGROUP_SCHED
1154         select FAIR_GROUP_SCHED
1155         help
1156           This option optimizes the scheduler for common desktop workloads by
1157           automatically creating and populating task groups.  This separation
1158           of workloads isolates aggressive CPU burners (like build jobs) from
1159           desktop applications.  Task group autogeneration is currently based
1160           upon task session.
1161 
1162 config MM_OWNER
1163         bool
1164 
1165 config SYSFS_DEPRECATED
1166         bool "Enable deprecated sysfs features to support old userspace tools"
1167         depends on SYSFS
1168         default n
1169         help
1170           This option adds code that switches the layout of the "block" class
1171           devices, to not show up in /sys/class/block/, but only in
1172           /sys/block/.
1173 
1174           This switch is only active when the sysfs.deprecated=1 boot option is
1175           passed or the SYSFS_DEPRECATED_V2 option is set.
1176 
1177           This option allows new kernels to run on old distributions and tools,
1178           which might get confused by /sys/class/block/. Since 2007/2008 all
1179           major distributions and tools handle this just fine.
1180 
1181           Recent distributions and userspace tools after 2009/2010 depend on
1182           the existence of /sys/class/block/, and will not work with this
1183           option enabled.
1184 
1185           Only if you are using a new kernel on an old distribution, you might
1186           need to say Y here.
1187 
1188 config SYSFS_DEPRECATED_V2
1189         bool "Enable deprecated sysfs features by default"
1190         default n
1191         depends on SYSFS
1192         depends on SYSFS_DEPRECATED
1193         help
1194           Enable deprecated sysfs by default.
1195 
1196           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1197           option.
1198 
1199           Only if you are using a new kernel on an old distribution, you might
1200           need to say Y here. Even then, odds are you would not need it
1201           enabled, you can always pass the boot option if absolutely necessary.
1202 
1203 config RELAY
1204         bool "Kernel->user space relay support (formerly relayfs)"
1205         help
1206           This option enables support for relay interface support in
1207           certain file systems (such as debugfs).
1208           It is designed to provide an efficient mechanism for tools and
1209           facilities to relay large amounts of data from kernel space to
1210           user space.
1211 
1212           If unsure, say N.
1213 
1214 config BLK_DEV_INITRD
1215         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1216         depends on BROKEN || !FRV
1217         help
1218           The initial RAM filesystem is a ramfs which is loaded by the
1219           boot loader (loadlin or lilo) and that is mounted as root
1220           before the normal boot procedure. It is typically used to
1221           load modules needed to mount the "real" root file system,
1222           etc. See <file:Documentation/initrd.txt> for details.
1223 
1224           If RAM disk support (BLK_DEV_RAM) is also included, this
1225           also enables initial RAM disk (initrd) support and adds
1226           15 Kbytes (more on some other architectures) to the kernel size.
1227 
1228           If unsure say Y.
1229 
1230 if BLK_DEV_INITRD
1231 
1232 source "usr/Kconfig"
1233 
1234 endif
1235 
1236 config CC_OPTIMIZE_FOR_SIZE
1237         bool "Optimize for size"
1238         help
1239           Enabling this option will pass "-Os" instead of "-O2" to gcc
1240           resulting in a smaller kernel.
1241 
1242           If unsure, say N.
1243 
1244 config SYSCTL
1245         bool
1246 
1247 config ANON_INODES
1248         bool
1249 
1250 config HAVE_UID16
1251         bool
1252 
1253 config SYSCTL_EXCEPTION_TRACE
1254         bool
1255         help
1256           Enable support for /proc/sys/debug/exception-trace.
1257 
1258 config SYSCTL_ARCH_UNALIGN_NO_WARN
1259         bool
1260         help
1261           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1262           Allows arch to define/use @no_unaligned_warning to possibly warn
1263           about unaligned access emulation going on under the hood.
1264 
1265 config SYSCTL_ARCH_UNALIGN_ALLOW
1266         bool
1267         help
1268           Enable support for /proc/sys/kernel/unaligned-trap
1269           Allows arches to define/use @unaligned_enabled to runtime toggle
1270           the unaligned access emulation.
1271           see arch/parisc/kernel/unaligned.c for reference
1272 
1273 config HAVE_PCSPKR_PLATFORM
1274         bool
1275 
1276 menuconfig EXPERT
1277         bool "Configure standard kernel features (expert users)"
1278         # Unhide debug options, to make the on-by-default options visible
1279         select DEBUG_KERNEL
1280         help
1281           This option allows certain base kernel options and settings
1282           to be disabled or tweaked. This is for specialized
1283           environments which can tolerate a "non-standard" kernel.
1284           Only use this if you really know what you are doing.
1285 
1286 config UID16
1287         bool "Enable 16-bit UID system calls" if EXPERT
1288         depends on HAVE_UID16
1289         default y
1290         help
1291           This enables the legacy 16-bit UID syscall wrappers.
1292 
1293 config SYSCTL_SYSCALL
1294         bool "Sysctl syscall support" if EXPERT
1295         depends on PROC_SYSCTL
1296         default n
1297         select SYSCTL
1298         ---help---
1299           sys_sysctl uses binary paths that have been found challenging
1300           to properly maintain and use.  The interface in /proc/sys
1301           using paths with ascii names is now the primary path to this
1302           information.
1303 
1304           Almost nothing using the binary sysctl interface so if you are
1305           trying to save some space it is probably safe to disable this,
1306           making your kernel marginally smaller.
1307 
1308           If unsure say N here.
1309 
1310 config KALLSYMS
1311          bool "Load all symbols for debugging/ksymoops" if EXPERT
1312          default y
1313          help
1314            Say Y here to let the kernel print out symbolic crash information and
1315            symbolic stack backtraces. This increases the size of the kernel
1316            somewhat, as all symbols have to be loaded into the kernel image.
1317 
1318 config KALLSYMS_ALL
1319         bool "Include all symbols in kallsyms"
1320         depends on DEBUG_KERNEL && KALLSYMS
1321         help
1322            Normally kallsyms only contains the symbols of functions for nicer
1323            OOPS messages and backtraces (i.e., symbols from the text and inittext
1324            sections). This is sufficient for most cases. And only in very rare
1325            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1326            names of variables from the data sections, etc).
1327 
1328            This option makes sure that all symbols are loaded into the kernel
1329            image (i.e., symbols from all sections) in cost of increased kernel
1330            size (depending on the kernel configuration, it may be 300KiB or
1331            something like this).
1332 
1333            Say N unless you really need all symbols.
1334 
1335 config PRINTK
1336         default y
1337         bool "Enable support for printk" if EXPERT
1338         select IRQ_WORK
1339         help
1340           This option enables normal printk support. Removing it
1341           eliminates most of the message strings from the kernel image
1342           and makes the kernel more or less silent. As this makes it
1343           very difficult to diagnose system problems, saying N here is
1344           strongly discouraged.
1345 
1346 config BUG
1347         bool "BUG() support" if EXPERT
1348         default y
1349         help
1350           Disabling this option eliminates support for BUG and WARN, reducing
1351           the size of your kernel image and potentially quietly ignoring
1352           numerous fatal conditions. You should only consider disabling this
1353           option for embedded systems with no facilities for reporting errors.
1354           Just say Y.
1355 
1356 config ELF_CORE
1357         depends on COREDUMP
1358         default y
1359         bool "Enable ELF core dumps" if EXPERT
1360         help
1361           Enable support for generating core dumps. Disabling saves about 4k.
1362 
1363 
1364 config PCSPKR_PLATFORM
1365         bool "Enable PC-Speaker support" if EXPERT
1366         depends on HAVE_PCSPKR_PLATFORM
1367         select I8253_LOCK
1368         default y
1369         help
1370           This option allows to disable the internal PC-Speaker
1371           support, saving some memory.
1372 
1373 config BASE_FULL
1374         default y
1375         bool "Enable full-sized data structures for core" if EXPERT
1376         help
1377           Disabling this option reduces the size of miscellaneous core
1378           kernel data structures. This saves memory on small machines,
1379           but may reduce performance.
1380 
1381 config FUTEX
1382         bool "Enable futex support" if EXPERT
1383         default y
1384         select RT_MUTEXES
1385         help
1386           Disabling this option will cause the kernel to be built without
1387           support for "fast userspace mutexes".  The resulting kernel may not
1388           run glibc-based applications correctly.
1389 
1390 config EPOLL
1391         bool "Enable eventpoll support" if EXPERT
1392         default y
1393         select ANON_INODES
1394         help
1395           Disabling this option will cause the kernel to be built without
1396           support for epoll family of system calls.
1397 
1398 config SIGNALFD
1399         bool "Enable signalfd() system call" if EXPERT
1400         select ANON_INODES
1401         default y
1402         help
1403           Enable the signalfd() system call that allows to receive signals
1404           on a file descriptor.
1405 
1406           If unsure, say Y.
1407 
1408 config TIMERFD
1409         bool "Enable timerfd() system call" if EXPERT
1410         select ANON_INODES
1411         default y
1412         help
1413           Enable the timerfd() system call that allows to receive timer
1414           events on a file descriptor.
1415 
1416           If unsure, say Y.
1417 
1418 config EVENTFD
1419         bool "Enable eventfd() system call" if EXPERT
1420         select ANON_INODES
1421         default y
1422         help
1423           Enable the eventfd() system call that allows to receive both
1424           kernel notification (ie. KAIO) or userspace notifications.
1425 
1426           If unsure, say Y.
1427 
1428 config SHMEM
1429         bool "Use full shmem filesystem" if EXPERT
1430         default y
1431         depends on MMU
1432         help
1433           The shmem is an internal filesystem used to manage shared memory.
1434           It is backed by swap and manages resource limits. It is also exported
1435           to userspace as tmpfs if TMPFS is enabled. Disabling this
1436           option replaces shmem and tmpfs with the much simpler ramfs code,
1437           which may be appropriate on small systems without swap.
1438 
1439 config AIO
1440         bool "Enable AIO support" if EXPERT
1441         default y
1442         help
1443           This option enables POSIX asynchronous I/O which may by used
1444           by some high performance threaded applications. Disabling
1445           this option saves about 7k.
1446 
1447 config PCI_QUIRKS
1448         default y
1449         bool "Enable PCI quirk workarounds" if EXPERT
1450         depends on PCI
1451         help
1452           This enables workarounds for various PCI chipset
1453           bugs/quirks. Disable this only if your target machine is
1454           unaffected by PCI quirks.
1455 
1456 config EMBEDDED
1457         bool "Embedded system"
1458         select EXPERT
1459         help
1460           This option should be enabled if compiling the kernel for
1461           an embedded system so certain expert options are available
1462           for configuration.
1463 
1464 config HAVE_PERF_EVENTS
1465         bool
1466         help
1467           See tools/perf/design.txt for details.
1468 
1469 config PERF_USE_VMALLOC
1470         bool
1471         help
1472           See tools/perf/design.txt for details
1473 
1474 menu "Kernel Performance Events And Counters"
1475 
1476 config PERF_EVENTS
1477         bool "Kernel performance events and counters"
1478         default y if PROFILING
1479         depends on HAVE_PERF_EVENTS
1480         select ANON_INODES
1481         select IRQ_WORK
1482         help
1483           Enable kernel support for various performance events provided
1484           by software and hardware.
1485 
1486           Software events are supported either built-in or via the
1487           use of generic tracepoints.
1488 
1489           Most modern CPUs support performance events via performance
1490           counter registers. These registers count the number of certain
1491           types of hw events: such as instructions executed, cachemisses
1492           suffered, or branches mis-predicted - without slowing down the
1493           kernel or applications. These registers can also trigger interrupts
1494           when a threshold number of events have passed - and can thus be
1495           used to profile the code that runs on that CPU.
1496 
1497           The Linux Performance Event subsystem provides an abstraction of
1498           these software and hardware event capabilities, available via a
1499           system call and used by the "perf" utility in tools/perf/. It
1500           provides per task and per CPU counters, and it provides event
1501           capabilities on top of those.
1502 
1503           Say Y if unsure.
1504 
1505 config DEBUG_PERF_USE_VMALLOC
1506         default n
1507         bool "Debug: use vmalloc to back perf mmap() buffers"
1508         depends on PERF_EVENTS && DEBUG_KERNEL
1509         select PERF_USE_VMALLOC
1510         help
1511          Use vmalloc memory to back perf mmap() buffers.
1512 
1513          Mostly useful for debugging the vmalloc code on platforms
1514          that don't require it.
1515 
1516          Say N if unsure.
1517 
1518 endmenu
1519 
1520 config VM_EVENT_COUNTERS
1521         default y
1522         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1523         help
1524           VM event counters are needed for event counts to be shown.
1525           This option allows the disabling of the VM event counters
1526           on EXPERT systems.  /proc/vmstat will only show page counts
1527           if VM event counters are disabled.
1528 
1529 config SLUB_DEBUG
1530         default y
1531         bool "Enable SLUB debugging support" if EXPERT
1532         depends on SLUB && SYSFS
1533         help
1534           SLUB has extensive debug support features. Disabling these can
1535           result in significant savings in code size. This also disables
1536           SLUB sysfs support. /sys/slab will not exist and there will be
1537           no support for cache validation etc.
1538 
1539 config COMPAT_BRK
1540         bool "Disable heap randomization"
1541         default y
1542         help
1543           Randomizing heap placement makes heap exploits harder, but it
1544           also breaks ancient binaries (including anything libc5 based).
1545           This option changes the bootup default to heap randomization
1546           disabled, and can be overridden at runtime by setting
1547           /proc/sys/kernel/randomize_va_space to 2.
1548 
1549           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1550 
1551 choice
1552         prompt "Choose SLAB allocator"
1553         default SLUB
1554         help
1555            This option allows to select a slab allocator.
1556 
1557 config SLAB
1558         bool "SLAB"
1559         help
1560           The regular slab allocator that is established and known to work
1561           well in all environments. It organizes cache hot objects in
1562           per cpu and per node queues.
1563 
1564 config SLUB
1565         bool "SLUB (Unqueued Allocator)"
1566         help
1567            SLUB is a slab allocator that minimizes cache line usage
1568            instead of managing queues of cached objects (SLAB approach).
1569            Per cpu caching is realized using slabs of objects instead
1570            of queues of objects. SLUB can use memory efficiently
1571            and has enhanced diagnostics. SLUB is the default choice for
1572            a slab allocator.
1573 
1574 config SLOB
1575         depends on EXPERT
1576         bool "SLOB (Simple Allocator)"
1577         help
1578            SLOB replaces the stock allocator with a drastically simpler
1579            allocator. SLOB is generally more space efficient but
1580            does not perform as well on large systems.
1581 
1582 endchoice
1583 
1584 config SLUB_CPU_PARTIAL
1585         default y
1586         depends on SLUB && SMP
1587         bool "SLUB per cpu partial cache"
1588         help
1589           Per cpu partial caches accellerate objects allocation and freeing
1590           that is local to a processor at the price of more indeterminism
1591           in the latency of the free. On overflow these caches will be cleared
1592           which requires the taking of locks that may cause latency spikes.
1593           Typically one would choose no for a realtime system.
1594 
1595 config MMAP_ALLOW_UNINITIALIZED
1596         bool "Allow mmapped anonymous memory to be uninitialized"
1597         depends on EXPERT && !MMU
1598         default n
1599         help
1600           Normally, and according to the Linux spec, anonymous memory obtained
1601           from mmap() has it's contents cleared before it is passed to
1602           userspace.  Enabling this config option allows you to request that
1603           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1604           providing a huge performance boost.  If this option is not enabled,
1605           then the flag will be ignored.
1606 
1607           This is taken advantage of by uClibc's malloc(), and also by
1608           ELF-FDPIC binfmt's brk and stack allocator.
1609 
1610           Because of the obvious security issues, this option should only be
1611           enabled on embedded devices where you control what is run in
1612           userspace.  Since that isn't generally a problem on no-MMU systems,
1613           it is normally safe to say Y here.
1614 
1615           See Documentation/nommu-mmap.txt for more information.
1616 
1617 config PROFILING
1618         bool "Profiling support"
1619         help
1620           Say Y here to enable the extended profiling support mechanisms used
1621           by profilers such as OProfile.
1622 
1623 #
1624 # Place an empty function call at each tracepoint site. Can be
1625 # dynamically changed for a probe function.
1626 #
1627 config TRACEPOINTS
1628         bool
1629 
1630 source "arch/Kconfig"
1631 
1632 endmenu         # General setup
1633 
1634 config HAVE_GENERIC_DMA_COHERENT
1635         bool
1636         default n
1637 
1638 config SLABINFO
1639         bool
1640         depends on PROC_FS
1641         depends on SLAB || SLUB_DEBUG
1642         default y
1643 
1644 config RT_MUTEXES
1645         boolean
1646 
1647 config BASE_SMALL
1648         int
1649         default 0 if BASE_FULL
1650         default 1 if !BASE_FULL
1651 
1652 config SYSTEM_TRUSTED_KEYRING
1653         bool "Provide system-wide ring of trusted keys"
1654         depends on KEYS
1655         help
1656           Provide a system keyring to which trusted keys can be added.  Keys in
1657           the keyring are considered to be trusted.  Keys may be added at will
1658           by the kernel from compiled-in data and from hardware key stores, but
1659           userspace may only add extra keys if those keys can be verified by
1660           keys already in the keyring.
1661 
1662           Keys in this keyring are used by module signature checking.
1663 
1664 menuconfig MODULES
1665         bool "Enable loadable module support"
1666         option modules
1667         help
1668           Kernel modules are small pieces of compiled code which can
1669           be inserted in the running kernel, rather than being
1670           permanently built into the kernel.  You use the "modprobe"
1671           tool to add (and sometimes remove) them.  If you say Y here,
1672           many parts of the kernel can be built as modules (by
1673           answering M instead of Y where indicated): this is most
1674           useful for infrequently used options which are not required
1675           for booting.  For more information, see the man pages for
1676           modprobe, lsmod, modinfo, insmod and rmmod.
1677 
1678           If you say Y here, you will need to run "make
1679           modules_install" to put the modules under /lib/modules/
1680           where modprobe can find them (you may need to be root to do
1681           this).
1682 
1683           If unsure, say Y.
1684 
1685 if MODULES
1686 
1687 config MODULE_FORCE_LOAD
1688         bool "Forced module loading"
1689         default n
1690         help
1691           Allow loading of modules without version information (ie. modprobe
1692           --force).  Forced module loading sets the 'F' (forced) taint flag and
1693           is usually a really bad idea.
1694 
1695 config MODULE_UNLOAD
1696         bool "Module unloading"
1697         help
1698           Without this option you will not be able to unload any
1699           modules (note that some modules may not be unloadable
1700           anyway), which makes your kernel smaller, faster
1701           and simpler.  If unsure, say Y.
1702 
1703 config MODULE_FORCE_UNLOAD
1704         bool "Forced module unloading"
1705         depends on MODULE_UNLOAD
1706         help
1707           This option allows you to force a module to unload, even if the
1708           kernel believes it is unsafe: the kernel will remove the module
1709           without waiting for anyone to stop using it (using the -f option to
1710           rmmod).  This is mainly for kernel developers and desperate users.
1711           If unsure, say N.
1712 
1713 config MODVERSIONS
1714         bool "Module versioning support"
1715         help
1716           Usually, you have to use modules compiled with your kernel.
1717           Saying Y here makes it sometimes possible to use modules
1718           compiled for different kernels, by adding enough information
1719           to the modules to (hopefully) spot any changes which would
1720           make them incompatible with the kernel you are running.  If
1721           unsure, say N.
1722 
1723 config MODULE_SRCVERSION_ALL
1724         bool "Source checksum for all modules"
1725         help
1726           Modules which contain a MODULE_VERSION get an extra "srcversion"
1727           field inserted into their modinfo section, which contains a
1728           sum of the source files which made it.  This helps maintainers
1729           see exactly which source was used to build a module (since
1730           others sometimes change the module source without updating
1731           the version).  With this option, such a "srcversion" field
1732           will be created for all modules.  If unsure, say N.
1733 
1734 config MODULE_SIG
1735         bool "Module signature verification"
1736         depends on MODULES
1737         select SYSTEM_TRUSTED_KEYRING
1738         select KEYS
1739         select CRYPTO
1740         select ASYMMETRIC_KEY_TYPE
1741         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1742         select PUBLIC_KEY_ALGO_RSA
1743         select ASN1
1744         select OID_REGISTRY
1745         select X509_CERTIFICATE_PARSER
1746         help
1747           Check modules for valid signatures upon load: the signature
1748           is simply appended to the module. For more information see
1749           Documentation/module-signing.txt.
1750 
1751           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1752           module DOES NOT get stripped after being signed.  This includes the
1753           debuginfo strip done by some packagers (such as rpmbuild) and
1754           inclusion into an initramfs that wants the module size reduced.
1755 
1756 config MODULE_SIG_FORCE
1757         bool "Require modules to be validly signed"
1758         depends on MODULE_SIG
1759         help
1760           Reject unsigned modules or signed modules for which we don't have a
1761           key.  Without this, such modules will simply taint the kernel.
1762 
1763 config MODULE_SIG_ALL
1764         bool "Automatically sign all modules"
1765         default y
1766         depends on MODULE_SIG
1767         help
1768           Sign all modules during make modules_install. Without this option,
1769           modules must be signed manually, using the scripts/sign-file tool.
1770 
1771 comment "Do not forget to sign required modules with scripts/sign-file"
1772         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1773 
1774 choice
1775         prompt "Which hash algorithm should modules be signed with?"
1776         depends on MODULE_SIG
1777         help
1778           This determines which sort of hashing algorithm will be used during
1779           signature generation.  This algorithm _must_ be built into the kernel
1780           directly so that signature verification can take place.  It is not
1781           possible to load a signed module containing the algorithm to check
1782           the signature on that module.
1783 
1784 config MODULE_SIG_SHA1
1785         bool "Sign modules with SHA-1"
1786         select CRYPTO_SHA1
1787 
1788 config MODULE_SIG_SHA224
1789         bool "Sign modules with SHA-224"
1790         select CRYPTO_SHA256
1791 
1792 config MODULE_SIG_SHA256
1793         bool "Sign modules with SHA-256"
1794         select CRYPTO_SHA256
1795 
1796 config MODULE_SIG_SHA384
1797         bool "Sign modules with SHA-384"
1798         select CRYPTO_SHA512
1799 
1800 config MODULE_SIG_SHA512
1801         bool "Sign modules with SHA-512"
1802         select CRYPTO_SHA512
1803 
1804 endchoice
1805 
1806 config MODULE_SIG_HASH
1807         string
1808         depends on MODULE_SIG
1809         default "sha1" if MODULE_SIG_SHA1
1810         default "sha224" if MODULE_SIG_SHA224
1811         default "sha256" if MODULE_SIG_SHA256
1812         default "sha384" if MODULE_SIG_SHA384
1813         default "sha512" if MODULE_SIG_SHA512
1814 
1815 endif # MODULES
1816 
1817 config INIT_ALL_POSSIBLE
1818         bool
1819         help
1820           Back when each arch used to define their own cpu_online_mask and
1821           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1822           with all 1s, and others with all 0s.  When they were centralised,
1823           it was better to provide this option than to break all the archs
1824           and have several arch maintainers pursuing me down dark alleys.
1825 
1826 config STOP_MACHINE
1827         bool
1828         default y
1829         depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1830         help
1831           Need stop_machine() primitive.
1832 
1833 source "block/Kconfig"
1834 
1835 config PREEMPT_NOTIFIERS
1836         bool
1837 
1838 config PADATA
1839         depends on SMP
1840         bool
1841 
1842 # Can be selected by architectures with broken toolchains
1843 # that get confused by correct const<->read_only section
1844 # mappings
1845 config BROKEN_RODATA
1846         bool
1847 
1848 config ASN1
1849         tristate
1850         help
1851           Build a simple ASN.1 grammar compiler that produces a bytecode output
1852           that can be interpreted by the ASN.1 stream decoder and used to
1853           inform it as to what tags are to be expected in a stream and what
1854           functions to call on what tags.
1855 
1856 source "kernel/Kconfig.locks"

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