1config ARCH
2 string
3 option env="ARCH"
4
5config KERNELVERSION
6 string
7 option env="KERNELVERSION"
8
9config 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
19config CONSTRUCTORS
20 bool
21 depends on !UML
22
23config IRQ_WORK
24 bool
25
26config BUILDTIME_EXTABLE_SORT
27 bool
28
29config THREAD_INFO_IN_TASK
30 bool
31 help
32 Select this to move thread_info off the stack into task_struct. To
33 make this work, an arch will need to remove all thread_info fields
34 except flags and fix any runtime bugs.
35
36 One subtle change that will be needed is to use try_get_task_stack()
37 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
38
39menu "General setup"
40
41config BROKEN
42 bool
43
44config BROKEN_ON_SMP
45 bool
46 depends on BROKEN || !SMP
47 default y
48
49config INIT_ENV_ARG_LIMIT
50 int
51 default 32 if !UML
52 default 128 if UML
53 help
54 Maximum of each of the number of arguments and environment
55 variables passed to init from the kernel command line.
56
57
58config CROSS_COMPILE
59 string "Cross-compiler tool prefix"
60 help
61 Same as running 'make CROSS_COMPILE=prefix-' but stored for
62 default make runs in this kernel build directory. You don't
63 need to set this unless you want the configured kernel build
64 directory to select the cross-compiler automatically.
65
66config COMPILE_TEST
67 bool "Compile also drivers which will not load"
68 depends on !UML
69 default n
70 help
71 Some drivers can be compiled on a different platform than they are
72 intended to be run on. Despite they cannot be loaded there (or even
73 when they load they cannot be used due to missing HW support),
74 developers still, opposing to distributors, might want to build such
75 drivers to compile-test them.
76
77 If you are a developer and want to build everything available, say Y
78 here. If you are a user/distributor, say N here to exclude useless
79 drivers to be distributed.
80
81config LOCALVERSION
82 string "Local version - append to kernel release"
83 help
84 Append an extra string to the end of your kernel version.
85 This will show up when you type uname, for example.
86 The string you set here will be appended after the contents of
87 any files with a filename matching localversion* in your
88 object and source tree, in that order. Your total string can
89 be a maximum of 64 characters.
90
91config LOCALVERSION_AUTO
92 bool "Automatically append version information to the version string"
93 default y
94 depends on !COMPILE_TEST
95 help
96 This will try to automatically determine if the current tree is a
97 release tree by looking for git tags that belong to the current
98 top of tree revision.
99
100 A string of the format -gxxxxxxxx will be added to the localversion
101 if a git-based tree is found. The string generated by this will be
102 appended after any matching localversion* files, and after the value
103 set in CONFIG_LOCALVERSION.
104
105 (The actual string used here is the first eight characters produced
106 by running the command:
107
108 $ git rev-parse --verify HEAD
109
110 which is done within the script "scripts/setlocalversion".)
111
112config HAVE_KERNEL_GZIP
113 bool
114
115config HAVE_KERNEL_BZIP2
116 bool
117
118config HAVE_KERNEL_LZMA
119 bool
120
121config HAVE_KERNEL_XZ
122 bool
123
124config HAVE_KERNEL_LZO
125 bool
126
127config HAVE_KERNEL_LZ4
128 bool
129
130choice
131 prompt "Kernel compression mode"
132 default KERNEL_GZIP
133 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
134 help
135 The linux kernel is a kind of self-extracting executable.
136 Several compression algorithms are available, which differ
137 in efficiency, compression and decompression speed.
138 Compression speed is only relevant when building a kernel.
139 Decompression speed is relevant at each boot.
140
141 If you have any problems with bzip2 or lzma compressed
142 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
143 version of this functionality (bzip2 only), for 2.4, was
144 supplied by Christian Ludwig)
145
146 High compression options are mostly useful for users, who
147 are low on disk space (embedded systems), but for whom ram
148 size matters less.
149
150 If in doubt, select 'gzip'
151
152config KERNEL_GZIP
153 bool "Gzip"
154 depends on HAVE_KERNEL_GZIP
155 help
156 The old and tried gzip compression. It provides a good balance
157 between compression ratio and decompression speed.
158
159config KERNEL_BZIP2
160 bool "Bzip2"
161 depends on HAVE_KERNEL_BZIP2
162 help
163 Its compression ratio and speed is intermediate.
164 Decompression speed is slowest among the choices. The kernel
165 size is about 10% smaller with bzip2, in comparison to gzip.
166 Bzip2 uses a large amount of memory. For modern kernels you
167 will need at least 8MB RAM or more for booting.
168
169config KERNEL_LZMA
170 bool "LZMA"
171 depends on HAVE_KERNEL_LZMA
172 help
173 This compression algorithm's ratio is best. Decompression speed
174 is between gzip and bzip2. Compression is slowest.
175 The kernel size is about 33% smaller with LZMA in comparison to gzip.
176
177config KERNEL_XZ
178 bool "XZ"
179 depends on HAVE_KERNEL_XZ
180 help
181 XZ uses the LZMA2 algorithm and instruction set specific
182 BCJ filters which can improve compression ratio of executable
183 code. The size of the kernel is about 30% smaller with XZ in
184 comparison to gzip. On architectures for which there is a BCJ
185 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
186 will create a few percent smaller kernel than plain LZMA.
187
188 The speed is about the same as with LZMA: The decompression
189 speed of XZ is better than that of bzip2 but worse than gzip
190 and LZO. Compression is slow.
191
192config KERNEL_LZO
193 bool "LZO"
194 depends on HAVE_KERNEL_LZO
195 help
196 Its compression ratio is the poorest among the choices. The kernel
197 size is about 10% bigger than gzip; however its speed
198 (both compression and decompression) is the fastest.
199
200config KERNEL_LZ4
201 bool "LZ4"
202 depends on HAVE_KERNEL_LZ4
203 help
204 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
205 A preliminary version of LZ4 de/compression tool is available at
206 <https://code.google.com/p/lz4/>.
207
208 Its compression ratio is worse than LZO. The size of the kernel
209 is about 8% bigger than LZO. But the decompression speed is
210 faster than LZO.
211
212endchoice
213
214config DEFAULT_HOSTNAME
215 string "Default hostname"
216 default "(none)"
217 help
218 This option determines the default system hostname before userspace
219 calls sethostname(2). The kernel traditionally uses "(none)" here,
220 but you may wish to use a different default here to make a minimal
221 system more usable with less configuration.
222
223config SWAP
224 bool "Support for paging of anonymous memory (swap)"
225 depends on MMU && BLOCK
226 default y
227 help
228 This option allows you to choose whether you want to have support
229 for so called swap devices or swap files in your kernel that are
230 used to provide more virtual memory than the actual RAM present
231 in your computer. If unsure say Y.
232
233config SYSVIPC
234 bool "System V IPC"
235 ---help---
236 Inter Process Communication is a suite of library functions and
237 system calls which let processes (running programs) synchronize and
238 exchange information. It is generally considered to be a good thing,
239 and some programs won't run unless you say Y here. In particular, if
240 you want to run the DOS emulator dosemu under Linux (read the
241 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html
242 you'll need to say Y here.
243
244 You can find documentation about IPC with "info ipc" and also in
245 section 6.4 of the Linux Programmer's Guide, available from
246 <http://www.tldp.org/guides.html>.
247
248config SYSVIPC_SYSCTL
249 bool
250 depends on SYSVIPC
251 depends on SYSCTL
252 default y
253
254config POSIX_MQUEUE
255 bool "POSIX Message Queues"
256 depends on NET
257 ---help---
258 POSIX variant of message queues is a part of IPC. In POSIX message
259 queues every message has a priority which decides about succession
260 of receiving it by a process. If you want to compile and run
261 programs written e.g. for Solaris with use of its POSIX message
262 queues (functions mq_*) say Y here.
263
264 POSIX message queues are visible as a filesystem called 'mqueue'
265 and can be mounted somewhere if you want to do filesystem
266 operations on message queues.
267
268 If unsure, say Y.
269
270config POSIX_MQUEUE_SYSCTL
271 bool
272 depends on POSIX_MQUEUE
273 depends on SYSCTL
274 default y
275
276config CROSS_MEMORY_ATTACH
277 bool "Enable process_vm_readv/writev syscalls"
278 depends on MMU
279 default y
280 help
281 Enabling this option adds the system calls process_vm_readv and
282 process_vm_writev which allow a process with the correct privileges
283 to directly read from or write to another process' address space.
284 See the man page for more details.
285
286config FHANDLE
287 bool "open by fhandle syscalls" if EXPERT
288 select EXPORTFS
289 default y
290 help
291 If you say Y here, a user level program will be able to map
292 file names to handle and then later use the handle for
293 different file system operations. This is useful in implementing
294 userspace file servers, which now track files using handles instead
295 of names. The handle would remain the same even if file names
296 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
297 syscalls.
298
299config USELIB
300 bool "uselib syscall"
301 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
302 help
303 This option enables the uselib syscall, a system call used in the
304 dynamic linker from libc5 and earlier. glibc does not use this
305 system call. If you intend to run programs built on libc5 or
306 earlier, you may need to enable this syscall. Current systems
307 running glibc can safely disable this.
308
309config AUDIT
310 bool "Auditing support"
311 depends on NET
312 help
313 Enable auditing infrastructure that can be used with another
314 kernel subsystem, such as SELinux (which requires this for
315 logging of avc messages output). System call auditing is included
316 on architectures which support it.
317
318config HAVE_ARCH_AUDITSYSCALL
319 bool
320
321config AUDITSYSCALL
322 def_bool y
323 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
324
325config AUDIT_WATCH
326 def_bool y
327 depends on AUDITSYSCALL
328 select FSNOTIFY
329
330config AUDIT_TREE
331 def_bool y
332 depends on AUDITSYSCALL
333 select FSNOTIFY
334
335source "kernel/irq/Kconfig"
336source "kernel/time/Kconfig"
337
338menu "CPU/Task time and stats accounting"
339
340config VIRT_CPU_ACCOUNTING
341 bool
342
343choice
344 prompt "Cputime accounting"
345 default TICK_CPU_ACCOUNTING if !PPC64
346 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
347
348
349config TICK_CPU_ACCOUNTING
350 bool "Simple tick based cputime accounting"
351 depends on !S390 && !NO_HZ_FULL
352 help
353 This is the basic tick based cputime accounting that maintains
354 statistics about user, system and idle time spent on per jiffies
355 granularity.
356
357 If unsure, say Y.
358
359config VIRT_CPU_ACCOUNTING_NATIVE
360 bool "Deterministic task and CPU time accounting"
361 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
362 select VIRT_CPU_ACCOUNTING
363 help
364 Select this option to enable more accurate task and CPU time
365 accounting. This is done by reading a CPU counter on each
366 kernel entry and exit and on transitions within the kernel
367 between system, softirq and hardirq state, so there is a
368 small performance impact. In the case of s390 or IBM POWER > 5,
369 this also enables accounting of stolen time on logically-partitioned
370 systems.
371
372config VIRT_CPU_ACCOUNTING_GEN
373 bool "Full dynticks CPU time accounting"
374 depends on HAVE_CONTEXT_TRACKING
375 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
376 select VIRT_CPU_ACCOUNTING
377 select CONTEXT_TRACKING
378 help
379 Select this option to enable task and CPU time accounting on full
380 dynticks systems. This accounting is implemented by watching every
381 kernel-user boundaries using the context tracking subsystem.
382 The accounting is thus performed at the expense of some significant
383 overhead.
384
385 For now this is only useful if you are working on the full
386 dynticks subsystem development.
387
388 If unsure, say N.
389
390endchoice
391
392config IRQ_TIME_ACCOUNTING
393 bool "Fine granularity task level IRQ time accounting"
394 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
395 help
396 Select this option to enable fine granularity task irq time
397 accounting. This is done by reading a timestamp on each
398 transitions between softirq and hardirq state, so there can be a
399 small performance impact.
400
401 If in doubt, say N here.
402
403config BSD_PROCESS_ACCT
404 bool "BSD Process Accounting"
405 depends on MULTIUSER
406 help
407 If you say Y here, a user level program will be able to instruct the
408 kernel (via a special system call) to write process accounting
409 information to a file: whenever a process exits, information about
410 that process will be appended to the file by the kernel. The
411 information includes things such as creation time, owning user,
412 command name, memory usage, controlling terminal etc. (the complete
413 list is in the struct acct in <file:include/linux/acct.h>). It is
414 up to the user level program to do useful things with this
415 information. This is generally a good idea, so say Y.
416
417config BSD_PROCESS_ACCT_V3
418 bool "BSD Process Accounting version 3 file format"
419 depends on BSD_PROCESS_ACCT
420 default n
421 help
422 If you say Y here, the process accounting information is written
423 in a new file format that also logs the process IDs of each
424 process and it's parent. Note that this file format is incompatible
425 with previous v0/v1/v2 file formats, so you will need updated tools
426 for processing it. A preliminary version of these tools is available
427 at <http://www.gnu.org/software/acct/>.
428
429config TASKSTATS
430 bool "Export task/process statistics through netlink"
431 depends on NET
432 depends on MULTIUSER
433 default n
434 help
435 Export selected statistics for tasks/processes through the
436 generic netlink interface. Unlike BSD process accounting, the
437 statistics are available during the lifetime of tasks/processes as
438 responses to commands. Like BSD accounting, they are sent to user
439 space on task exit.
440
441 Say N if unsure.
442
443config TASK_DELAY_ACCT
444 bool "Enable per-task delay accounting"
445 depends on TASKSTATS
446 select SCHED_INFO
447 help
448 Collect information on time spent by a task waiting for system
449 resources like cpu, synchronous block I/O completion and swapping
450 in pages. Such statistics can help in setting a task's priorities
451 relative to other tasks for cpu, io, rss limits etc.
452
453 Say N if unsure.
454
455config TASK_XACCT
456 bool "Enable extended accounting over taskstats"
457 depends on TASKSTATS
458 help
459 Collect extended task accounting data and send the data
460 to userland for processing over the taskstats interface.
461
462 Say N if unsure.
463
464config TASK_IO_ACCOUNTING
465 bool "Enable per-task storage I/O accounting"
466 depends on TASK_XACCT
467 help
468 Collect information on the number of bytes of storage I/O which this
469 task has caused.
470
471 Say N if unsure.
472
473endmenu
474
475menu "RCU Subsystem"
476
477config TREE_RCU
478 bool
479 default y if !PREEMPT && SMP
480 help
481 This option selects the RCU implementation that is
482 designed for very large SMP system with hundreds or
483 thousands of CPUs. It also scales down nicely to
484 smaller systems.
485
486config PREEMPT_RCU
487 bool
488 default y if PREEMPT
489 help
490 This option selects the RCU implementation that is
491 designed for very large SMP systems with hundreds or
492 thousands of CPUs, but for which real-time response
493 is also required. It also scales down nicely to
494 smaller systems.
495
496 Select this option if you are unsure.
497
498config TINY_RCU
499 bool
500 default y if !PREEMPT && !SMP
501 help
502 This option selects the RCU implementation that is
503 designed for UP systems from which real-time response
504 is not required. This option greatly reduces the
505 memory footprint of RCU.
506
507config RCU_EXPERT
508 bool "Make expert-level adjustments to RCU configuration"
509 default n
510 help
511 This option needs to be enabled if you wish to make
512 expert-level adjustments to RCU configuration. By default,
513 no such adjustments can be made, which has the often-beneficial
514 side-effect of preventing "make oldconfig" from asking you all
515 sorts of detailed questions about how you would like numerous
516 obscure RCU options to be set up.
517
518 Say Y if you need to make expert-level adjustments to RCU.
519
520 Say N if you are unsure.
521
522config SRCU
523 bool
524 help
525 This option selects the sleepable version of RCU. This version
526 permits arbitrary sleeping or blocking within RCU read-side critical
527 sections.
528
529config TASKS_RCU
530 bool
531 default n
532 depends on !UML
533 select SRCU
534 help
535 This option enables a task-based RCU implementation that uses
536 only voluntary context switch (not preemption!), idle, and
537 user-mode execution as quiescent states.
538
539config RCU_STALL_COMMON
540 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
541 help
542 This option enables RCU CPU stall code that is common between
543 the TINY and TREE variants of RCU. The purpose is to allow
544 the tiny variants to disable RCU CPU stall warnings, while
545 making these warnings mandatory for the tree variants.
546
547config CONTEXT_TRACKING
548 bool
549
550config CONTEXT_TRACKING_FORCE
551 bool "Force context tracking"
552 depends on CONTEXT_TRACKING
553 default y if !NO_HZ_FULL
554 help
555 The major pre-requirement for full dynticks to work is to
556 support the context tracking subsystem. But there are also
557 other dependencies to provide in order to make the full
558 dynticks working.
559
560 This option stands for testing when an arch implements the
561 context tracking backend but doesn't yet fullfill all the
562 requirements to make the full dynticks feature working.
563 Without the full dynticks, there is no way to test the support
564 for context tracking and the subsystems that rely on it: RCU
565 userspace extended quiescent state and tickless cputime
566 accounting. This option copes with the absence of the full
567 dynticks subsystem by forcing the context tracking on all
568 CPUs in the system.
569
570 Say Y only if you're working on the development of an
571 architecture backend for the context tracking.
572
573 Say N otherwise, this option brings an overhead that you
574 don't want in production.
575
576
577config RCU_FANOUT
578 int "Tree-based hierarchical RCU fanout value"
579 range 2 64 if 64BIT
580 range 2 32 if !64BIT
581 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
582 default 64 if 64BIT
583 default 32 if !64BIT
584 help
585 This option controls the fanout of hierarchical implementations
586 of RCU, allowing RCU to work efficiently on machines with
587 large numbers of CPUs. This value must be at least the fourth
588 root of NR_CPUS, which allows NR_CPUS to be insanely large.
589 The default value of RCU_FANOUT should be used for production
590 systems, but if you are stress-testing the RCU implementation
591 itself, small RCU_FANOUT values allow you to test large-system
592 code paths on small(er) systems.
593
594 Select a specific number if testing RCU itself.
595 Take the default if unsure.
596
597config RCU_FANOUT_LEAF
598 int "Tree-based hierarchical RCU leaf-level fanout value"
599 range 2 64 if 64BIT
600 range 2 32 if !64BIT
601 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
602 default 16
603 help
604 This option controls the leaf-level fanout of hierarchical
605 implementations of RCU, and allows trading off cache misses
606 against lock contention. Systems that synchronize their
607 scheduling-clock interrupts for energy-efficiency reasons will
608 want the default because the smaller leaf-level fanout keeps
609 lock contention levels acceptably low. Very large systems
610 (hundreds or thousands of CPUs) will instead want to set this
611 value to the maximum value possible in order to reduce the
612 number of cache misses incurred during RCU's grace-period
613 initialization. These systems tend to run CPU-bound, and thus
614 are not helped by synchronized interrupts, and thus tend to
615 skew them, which reduces lock contention enough that large
616 leaf-level fanouts work well.
617
618 Select a specific number if testing RCU itself.
619
620 Select the maximum permissible value for large systems.
621
622 Take the default if unsure.
623
624config RCU_FAST_NO_HZ
625 bool "Accelerate last non-dyntick-idle CPU's grace periods"
626 depends on NO_HZ_COMMON && SMP && RCU_EXPERT
627 default n
628 help
629 This option permits CPUs to enter dynticks-idle state even if
630 they have RCU callbacks queued, and prevents RCU from waking
631 these CPUs up more than roughly once every four jiffies (by
632 default, you can adjust this using the rcutree.rcu_idle_gp_delay
633 parameter), thus improving energy efficiency. On the other
634 hand, this option increases the duration of RCU grace periods,
635 for example, slowing down synchronize_rcu().
636
637 Say Y if energy efficiency is critically important, and you
638 don't care about increased grace-period durations.
639
640 Say N if you are unsure.
641
642config TREE_RCU_TRACE
643 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
644 select DEBUG_FS
645 help
646 This option provides tracing for the TREE_RCU and
647 PREEMPT_RCU implementations, permitting Makefile to
648 trivially select kernel/rcutree_trace.c.
649
650config RCU_BOOST
651 bool "Enable RCU priority boosting"
652 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
653 default n
654 help
655 This option boosts the priority of preempted RCU readers that
656 block the current preemptible RCU grace period for too long.
657 This option also prevents heavy loads from blocking RCU
658 callback invocation for all flavors of RCU.
659
660 Say Y here if you are working with real-time apps or heavy loads
661 Say N here if you are unsure.
662
663config RCU_KTHREAD_PRIO
664 int "Real-time priority to use for RCU worker threads"
665 range 1 99 if RCU_BOOST
666 range 0 99 if !RCU_BOOST
667 default 1 if RCU_BOOST
668 default 0 if !RCU_BOOST
669 depends on RCU_EXPERT
670 help
671 This option specifies the SCHED_FIFO priority value that will be
672 assigned to the rcuc/n and rcub/n threads and is also the value
673 used for RCU_BOOST (if enabled). If you are working with a
674 real-time application that has one or more CPU-bound threads
675 running at a real-time priority level, you should set
676 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
677 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
678 value of 1 is appropriate in the common case, which is real-time
679 applications that do not have any CPU-bound threads.
680
681 Some real-time applications might not have a single real-time
682 thread that saturates a given CPU, but instead might have
683 multiple real-time threads that, taken together, fully utilize
684 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
685 a priority higher than the lowest-priority thread that is
686 conspiring to prevent the CPU from running any non-real-time
687 tasks. For example, if one thread at priority 10 and another
688 thread at priority 5 are between themselves fully consuming
689 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
690 set to priority 6 or higher.
691
692 Specify the real-time priority, or take the default if unsure.
693
694config RCU_BOOST_DELAY
695 int "Milliseconds to delay boosting after RCU grace-period start"
696 range 0 3000
697 depends on RCU_BOOST
698 default 500
699 help
700 This option specifies the time to wait after the beginning of
701 a given grace period before priority-boosting preempted RCU
702 readers blocking that grace period. Note that any RCU reader
703 blocking an expedited RCU grace period is boosted immediately.
704
705 Accept the default if unsure.
706
707config RCU_NOCB_CPU
708 bool "Offload RCU callback processing from boot-selected CPUs"
709 depends on TREE_RCU || PREEMPT_RCU
710 depends on RCU_EXPERT || NO_HZ_FULL
711 default n
712 help
713 Use this option to reduce OS jitter for aggressive HPC or
714 real-time workloads. It can also be used to offload RCU
715 callback invocation to energy-efficient CPUs in battery-powered
716 asymmetric multiprocessors.
717
718 This option offloads callback invocation from the set of
719 CPUs specified at boot time by the rcu_nocbs parameter.
720 For each such CPU, a kthread ("rcuox/N") will be created to
721 invoke callbacks, where the "N" is the CPU being offloaded,
722 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
723 "s" for RCU-sched. Nothing prevents this kthread from running
724 on the specified CPUs, but (1) the kthreads may be preempted
725 between each callback, and (2) affinity or cgroups can be used
726 to force the kthreads to run on whatever set of CPUs is desired.
727
728 Say Y here if you want to help to debug reduced OS jitter.
729 Say N here if you are unsure.
730
731choice
732 prompt "Build-forced no-CBs CPUs"
733 default RCU_NOCB_CPU_NONE
734 depends on RCU_NOCB_CPU
735 help
736 This option allows no-CBs CPUs (whose RCU callbacks are invoked
737 from kthreads rather than from softirq context) to be specified
738 at build time. Additional no-CBs CPUs may be specified by
739 the rcu_nocbs= boot parameter.
740
741config RCU_NOCB_CPU_NONE
742 bool "No build_forced no-CBs CPUs"
743 help
744 This option does not force any of the CPUs to be no-CBs CPUs.
745 Only CPUs designated by the rcu_nocbs= boot parameter will be
746 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
747 kthreads whose names begin with "rcuo". All other CPUs will
748 invoke their own RCU callbacks in softirq context.
749
750 Select this option if you want to choose no-CBs CPUs at
751 boot time, for example, to allow testing of different no-CBs
752 configurations without having to rebuild the kernel each time.
753
754config RCU_NOCB_CPU_ZERO
755 bool "CPU 0 is a build_forced no-CBs CPU"
756 help
757 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
758 callbacks are invoked by a per-CPU kthread whose name begins
759 with "rcuo". Additional CPUs may be designated as no-CBs
760 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
761 All other CPUs will invoke their own RCU callbacks in softirq
762 context.
763
764 Select this if CPU 0 needs to be a no-CBs CPU for real-time
765 or energy-efficiency reasons, but the real reason it exists
766 is to ensure that randconfig testing covers mixed systems.
767
768config RCU_NOCB_CPU_ALL
769 bool "All CPUs are build_forced no-CBs CPUs"
770 help
771 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
772 boot parameter will be ignored. All CPUs' RCU callbacks will
773 be executed in the context of per-CPU rcuo kthreads created for
774 this purpose. Assuming that the kthreads whose names start with
775 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
776 on the remaining CPUs, but might decrease memory locality during
777 RCU-callback invocation, thus potentially degrading throughput.
778
779 Select this if all CPUs need to be no-CBs CPUs for real-time
780 or energy-efficiency reasons.
781
782endchoice
783
784config RCU_EXPEDITE_BOOT
785 bool
786 default n
787 help
788 This option enables expedited grace periods at boot time,
789 as if rcu_expedite_gp() had been invoked early in boot.
790 The corresponding rcu_unexpedite_gp() is invoked from
791 rcu_end_inkernel_boot(), which is intended to be invoked
792 at the end of the kernel-only boot sequence, just before
793 init is exec'ed.
794
795 Accept the default if unsure.
796
797endmenu
798
799config BUILD_BIN2C
800 bool
801 default n
802
803config IKCONFIG
804 tristate "Kernel .config support"
805 select BUILD_BIN2C
806 ---help---
807 This option enables the complete Linux kernel ".config" file
808 contents to be saved in the kernel. It provides documentation
809 of which kernel options are used in a running kernel or in an
810 on-disk kernel. This information can be extracted from the kernel
811 image file with the script scripts/extract-ikconfig and used as
812 input to rebuild the current kernel or to build another kernel.
813 It can also be extracted from a running kernel by reading
814 /proc/config.gz if enabled (below).
815
816config IKCONFIG_PROC
817 bool "Enable access to .config through /proc/config.gz"
818 depends on IKCONFIG && PROC_FS
819 ---help---
820 This option enables access to the kernel configuration file
821 through /proc/config.gz.
822
823config LOG_BUF_SHIFT
824 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
825 range 12 25
826 default 17
827 depends on PRINTK
828 help
829 Select the minimal kernel log buffer size as a power of 2.
830 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
831 parameter, see below. Any higher size also might be forced
832 by "log_buf_len" boot parameter.
833
834 Examples:
835 17 => 128 KB
836 16 => 64 KB
837 15 => 32 KB
838 14 => 16 KB
839 13 => 8 KB
840 12 => 4 KB
841
842config LOG_CPU_MAX_BUF_SHIFT
843 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
844 depends on SMP
845 range 0 21
846 default 12 if !BASE_SMALL
847 default 0 if BASE_SMALL
848 depends on PRINTK
849 help
850 This option allows to increase the default ring buffer size
851 according to the number of CPUs. The value defines the contribution
852 of each CPU as a power of 2. The used space is typically only few
853 lines however it might be much more when problems are reported,
854 e.g. backtraces.
855
856 The increased size means that a new buffer has to be allocated and
857 the original static one is unused. It makes sense only on systems
858 with more CPUs. Therefore this value is used only when the sum of
859 contributions is greater than the half of the default kernel ring
860 buffer as defined by LOG_BUF_SHIFT. The default values are set
861 so that more than 64 CPUs are needed to trigger the allocation.
862
863 Also this option is ignored when "log_buf_len" kernel parameter is
864 used as it forces an exact (power of two) size of the ring buffer.
865
866 The number of possible CPUs is used for this computation ignoring
867 hotplugging making the computation optimal for the worst case
868 scenario while allowing a simple algorithm to be used from bootup.
869
870 Examples shift values and their meaning:
871 17 => 128 KB for each CPU
872 16 => 64 KB for each CPU
873 15 => 32 KB for each CPU
874 14 => 16 KB for each CPU
875 13 => 8 KB for each CPU
876 12 => 4 KB for each CPU
877
878config NMI_LOG_BUF_SHIFT
879 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
880 range 10 21
881 default 13
882 depends on PRINTK_NMI
883 help
884 Select the size of a per-CPU buffer where NMI messages are temporary
885 stored. They are copied to the main log buffer in a safe context
886 to avoid a deadlock. The value defines the size as a power of 2.
887
888 NMI messages are rare and limited. The largest one is when
889 a backtrace is printed. It usually fits into 4KB. Select
890 8KB if you want to be on the safe side.
891
892 Examples:
893 17 => 128 KB for each CPU
894 16 => 64 KB for each CPU
895 15 => 32 KB for each CPU
896 14 => 16 KB for each CPU
897 13 => 8 KB for each CPU
898 12 => 4 KB for each CPU
899
900
901
902
903config HAVE_UNSTABLE_SCHED_CLOCK
904 bool
905
906config GENERIC_SCHED_CLOCK
907 bool
908
909
910
911
912
913config ARCH_SUPPORTS_NUMA_BALANCING
914 bool
915
916
917
918
919
920
921
922
923config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
924 bool
925
926
927
928
929config ARCH_SUPPORTS_INT128
930 bool
931
932
933
934
935config ARCH_WANT_NUMA_VARIABLE_LOCALITY
936 bool
937
938config NUMA_BALANCING
939 bool "Memory placement aware NUMA scheduler"
940 depends on ARCH_SUPPORTS_NUMA_BALANCING
941 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
942 depends on SMP && NUMA && MIGRATION
943 help
944 This option adds support for automatic NUMA aware memory/task placement.
945 The mechanism is quite primitive and is based on migrating memory when
946 it has references to the node the task is running on.
947
948 This system will be inactive on UMA systems.
949
950config NUMA_BALANCING_DEFAULT_ENABLED
951 bool "Automatically enable NUMA aware memory/task placement"
952 default y
953 depends on NUMA_BALANCING
954 help
955 If set, automatic NUMA balancing will be enabled if running on a NUMA
956 machine.
957
958menuconfig CGROUPS
959 bool "Control Group support"
960 select KERNFS
961 help
962 This option adds support for grouping sets of processes together, for
963 use with process control subsystems such as Cpusets, CFS, memory
964 controls or device isolation.
965 See
966 - Documentation/scheduler/sched-design-CFS.txt (CFS)
967 - Documentation/cgroup-v1/ (features for grouping, isolation
968 and resource control)
969
970 Say N if unsure.
971
972if CGROUPS
973
974config PAGE_COUNTER
975 bool
976
977config MEMCG
978 bool "Memory controller"
979 select PAGE_COUNTER
980 select EVENTFD
981 help
982 Provides control over the memory footprint of tasks in a cgroup.
983
984config MEMCG_SWAP
985 bool "Swap controller"
986 depends on MEMCG && SWAP
987 help
988 Provides control over the swap space consumed by tasks in a cgroup.
989
990config MEMCG_SWAP_ENABLED
991 bool "Swap controller enabled by default"
992 depends on MEMCG_SWAP
993 default y
994 help
995 Memory Resource Controller Swap Extension comes with its price in
996 a bigger memory consumption. General purpose distribution kernels
997 which want to enable the feature but keep it disabled by default
998 and let the user enable it by swapaccount=1 boot command line
999 parameter should have this option unselected.
1000 For those who want to have the feature enabled by default should
1001 select this option (if, for some reason, they need to disable it
1002 then swapaccount=0 does the trick).
1003
1004config BLK_CGROUP
1005 bool "IO controller"
1006 depends on BLOCK
1007 default n
1008 ---help---
1009 Generic block IO controller cgroup interface. This is the common
1010 cgroup interface which should be used by various IO controlling
1011 policies.
1012
1013 Currently, CFQ IO scheduler uses it to recognize task groups and
1014 control disk bandwidth allocation (proportional time slice allocation)
1015 to such task groups. It is also used by bio throttling logic in
1016 block layer to implement upper limit in IO rates on a device.
1017
1018 This option only enables generic Block IO controller infrastructure.
1019 One needs to also enable actual IO controlling logic/policy. For
1020 enabling proportional weight division of disk bandwidth in CFQ, set
1021 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1022 CONFIG_BLK_DEV_THROTTLING=y.
1023
1024 See Documentation/cgroup-v1/blkio-controller.txt for more information.
1025
1026config DEBUG_BLK_CGROUP
1027 bool "IO controller debugging"
1028 depends on BLK_CGROUP
1029 default n
1030 ---help---
1031 Enable some debugging help. Currently it exports additional stat
1032 files in a cgroup which can be useful for debugging.
1033
1034config CGROUP_WRITEBACK
1035 bool
1036 depends on MEMCG && BLK_CGROUP
1037 default y
1038
1039menuconfig CGROUP_SCHED
1040 bool "CPU controller"
1041 default n
1042 help
1043 This feature lets CPU scheduler recognize task groups and control CPU
1044 bandwidth allocation to such task groups. It uses cgroups to group
1045 tasks.
1046
1047if CGROUP_SCHED
1048config FAIR_GROUP_SCHED
1049 bool "Group scheduling for SCHED_OTHER"
1050 depends on CGROUP_SCHED
1051 default CGROUP_SCHED
1052
1053config CFS_BANDWIDTH
1054 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1055 depends on FAIR_GROUP_SCHED
1056 default n
1057 help
1058 This option allows users to define CPU bandwidth rates (limits) for
1059 tasks running within the fair group scheduler. Groups with no limit
1060 set are considered to be unconstrained and will run with no
1061 restriction.
1062 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1063
1064config RT_GROUP_SCHED
1065 bool "Group scheduling for SCHED_RR/FIFO"
1066 depends on CGROUP_SCHED
1067 default n
1068 help
1069 This feature lets you explicitly allocate real CPU bandwidth
1070 to task groups. If enabled, it will also make it impossible to
1071 schedule realtime tasks for non-root users until you allocate
1072 realtime bandwidth for them.
1073 See Documentation/scheduler/sched-rt-group.txt for more information.
1074
1075endif
1076
1077config CGROUP_PIDS
1078 bool "PIDs controller"
1079 help
1080 Provides enforcement of process number limits in the scope of a
1081 cgroup. Any attempt to fork more processes than is allowed in the
1082 cgroup will fail. PIDs are fundamentally a global resource because it
1083 is fairly trivial to reach PID exhaustion before you reach even a
1084 conservative kmemcg limit. As a result, it is possible to grind a
1085 system to halt without being limited by other cgroup policies. The
1086 PIDs controller is designed to stop this from happening.
1087
1088 It should be noted that organisational operations (such as attaching
1089 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1090 since the PIDs limit only affects a process's ability to fork, not to
1091 attach to a cgroup.
1092
1093config CGROUP_FREEZER
1094 bool "Freezer controller"
1095 help
1096 Provides a way to freeze and unfreeze all tasks in a
1097 cgroup.
1098
1099 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1100 controller includes important in-kernel memory consumers per default.
1101
1102 If you're using cgroup2, say N.
1103
1104config CGROUP_HUGETLB
1105 bool "HugeTLB controller"
1106 depends on HUGETLB_PAGE
1107 select PAGE_COUNTER
1108 default n
1109 help
1110 Provides a cgroup controller for HugeTLB pages.
1111 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1112 The limit is enforced during page fault. Since HugeTLB doesn't
1113 support page reclaim, enforcing the limit at page fault time implies
1114 that, the application will get SIGBUS signal if it tries to access
1115 HugeTLB pages beyond its limit. This requires the application to know
1116 beforehand how much HugeTLB pages it would require for its use. The
1117 control group is tracked in the third page lru pointer. This means
1118 that we cannot use the controller with huge page less than 3 pages.
1119
1120config CPUSETS
1121 bool "Cpuset controller"
1122 help
1123 This option will let you create and manage CPUSETs which
1124 allow dynamically partitioning a system into sets of CPUs and
1125 Memory Nodes and assigning tasks to run only within those sets.
1126 This is primarily useful on large SMP or NUMA systems.
1127
1128 Say N if unsure.
1129
1130config PROC_PID_CPUSET
1131 bool "Include legacy /proc/<pid>/cpuset file"
1132 depends on CPUSETS
1133 default y
1134
1135config CGROUP_DEVICE
1136 bool "Device controller"
1137 help
1138 Provides a cgroup controller implementing whitelists for
1139 devices which a process in the cgroup can mknod or open.
1140
1141config CGROUP_CPUACCT
1142 bool "Simple CPU accounting controller"
1143 help
1144 Provides a simple controller for monitoring the
1145 total CPU consumed by the tasks in a cgroup.
1146
1147config CGROUP_PERF
1148 bool "Perf controller"
1149 depends on PERF_EVENTS
1150 help
1151 This option extends the perf per-cpu mode to restrict monitoring
1152 to threads which belong to the cgroup specified and run on the
1153 designated cpu.
1154
1155 Say N if unsure.
1156
1157config CGROUP_DEBUG
1158 bool "Example controller"
1159 default n
1160 help
1161 This option enables a simple controller that exports
1162 debugging information about the cgroups framework.
1163
1164 Say N.
1165
1166endif
1167
1168config CHECKPOINT_RESTORE
1169 bool "Checkpoint/restore support" if EXPERT
1170 select PROC_CHILDREN
1171 default n
1172 help
1173 Enables additional kernel features in a sake of checkpoint/restore.
1174 In particular it adds auxiliary prctl codes to setup process text,
1175 data and heap segment sizes, and a few additional /proc filesystem
1176 entries.
1177
1178 If unsure, say N here.
1179
1180menuconfig NAMESPACES
1181 bool "Namespaces support" if EXPERT
1182 depends on MULTIUSER
1183 default !EXPERT
1184 help
1185 Provides the way to make tasks work with different objects using
1186 the same id. For example same IPC id may refer to different objects
1187 or same user id or pid may refer to different tasks when used in
1188 different namespaces.
1189
1190if NAMESPACES
1191
1192config UTS_NS
1193 bool "UTS namespace"
1194 default y
1195 help
1196 In this namespace tasks see different info provided with the
1197 uname() system call
1198
1199config IPC_NS
1200 bool "IPC namespace"
1201 depends on (SYSVIPC || POSIX_MQUEUE)
1202 default y
1203 help
1204 In this namespace tasks work with IPC ids which correspond to
1205 different IPC objects in different namespaces.
1206
1207config USER_NS
1208 bool "User namespace"
1209 default n
1210 help
1211 This allows containers, i.e. vservers, to use user namespaces
1212 to provide different user info for different servers.
1213
1214 When user namespaces are enabled in the kernel it is
1215 recommended that the MEMCG option also be enabled and that
1216 user-space use the memory control groups to limit the amount
1217 of memory a memory unprivileged users can use.
1218
1219 If unsure, say N.
1220
1221config PID_NS
1222 bool "PID Namespaces"
1223 default y
1224 help
1225 Support process id namespaces. This allows having multiple
1226 processes with the same pid as long as they are in different
1227 pid namespaces. This is a building block of containers.
1228
1229config NET_NS
1230 bool "Network namespace"
1231 depends on NET
1232 default y
1233 help
1234 Allow user space to create what appear to be multiple instances
1235 of the network stack.
1236
1237endif
1238
1239config SCHED_AUTOGROUP
1240 bool "Automatic process group scheduling"
1241 select CGROUPS
1242 select CGROUP_SCHED
1243 select FAIR_GROUP_SCHED
1244 help
1245 This option optimizes the scheduler for common desktop workloads by
1246 automatically creating and populating task groups. This separation
1247 of workloads isolates aggressive CPU burners (like build jobs) from
1248 desktop applications. Task group autogeneration is currently based
1249 upon task session.
1250
1251config SYSFS_DEPRECATED
1252 bool "Enable deprecated sysfs features to support old userspace tools"
1253 depends on SYSFS
1254 default n
1255 help
1256 This option adds code that switches the layout of the "block" class
1257 devices, to not show up in /sys/class/block/, but only in
1258 /sys/block/.
1259
1260 This switch is only active when the sysfs.deprecated=1 boot option is
1261 passed or the SYSFS_DEPRECATED_V2 option is set.
1262
1263 This option allows new kernels to run on old distributions and tools,
1264 which might get confused by /sys/class/block/. Since 2007/2008 all
1265 major distributions and tools handle this just fine.
1266
1267 Recent distributions and userspace tools after 2009/2010 depend on
1268 the existence of /sys/class/block/, and will not work with this
1269 option enabled.
1270
1271 Only if you are using a new kernel on an old distribution, you might
1272 need to say Y here.
1273
1274config SYSFS_DEPRECATED_V2
1275 bool "Enable deprecated sysfs features by default"
1276 default n
1277 depends on SYSFS
1278 depends on SYSFS_DEPRECATED
1279 help
1280 Enable deprecated sysfs by default.
1281
1282 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1283 option.
1284
1285 Only if you are using a new kernel on an old distribution, you might
1286 need to say Y here. Even then, odds are you would not need it
1287 enabled, you can always pass the boot option if absolutely necessary.
1288
1289config RELAY
1290 bool "Kernel->user space relay support (formerly relayfs)"
1291 select IRQ_WORK
1292 help
1293 This option enables support for relay interface support in
1294 certain file systems (such as debugfs).
1295 It is designed to provide an efficient mechanism for tools and
1296 facilities to relay large amounts of data from kernel space to
1297 user space.
1298
1299 If unsure, say N.
1300
1301config BLK_DEV_INITRD
1302 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1303 depends on BROKEN || !FRV
1304 help
1305 The initial RAM filesystem is a ramfs which is loaded by the
1306 boot loader (loadlin or lilo) and that is mounted as root
1307 before the normal boot procedure. It is typically used to
1308 load modules needed to mount the "real" root file system,
1309 etc. See <file:Documentation/initrd.txt> for details.
1310
1311 If RAM disk support (BLK_DEV_RAM) is also included, this
1312 also enables initial RAM disk (initrd) support and adds
1313 15 Kbytes (more on some other architectures) to the kernel size.
1314
1315 If unsure say Y.
1316
1317if BLK_DEV_INITRD
1318
1319source "usr/Kconfig"
1320
1321endif
1322
1323choice
1324 prompt "Compiler optimization level"
1325 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1326
1327config CC_OPTIMIZE_FOR_PERFORMANCE
1328 bool "Optimize for performance"
1329 help
1330 This is the default optimization level for the kernel, building
1331 with the "-O2" compiler flag for best performance and most
1332 helpful compile-time warnings.
1333
1334config CC_OPTIMIZE_FOR_SIZE
1335 bool "Optimize for size"
1336 help
1337 Enabling this option will pass "-Os" instead of "-O2" to
1338 your compiler resulting in a smaller kernel.
1339
1340 If unsure, say N.
1341
1342endchoice
1343
1344config SYSCTL
1345 bool
1346
1347config ANON_INODES
1348 bool
1349
1350config HAVE_UID16
1351 bool
1352
1353config SYSCTL_EXCEPTION_TRACE
1354 bool
1355 help
1356 Enable support for /proc/sys/debug/exception-trace.
1357
1358config SYSCTL_ARCH_UNALIGN_NO_WARN
1359 bool
1360 help
1361 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1362 Allows arch to define/use @no_unaligned_warning to possibly warn
1363 about unaligned access emulation going on under the hood.
1364
1365config SYSCTL_ARCH_UNALIGN_ALLOW
1366 bool
1367 help
1368 Enable support for /proc/sys/kernel/unaligned-trap
1369 Allows arches to define/use @unaligned_enabled to runtime toggle
1370 the unaligned access emulation.
1371 see arch/parisc/kernel/unaligned.c for reference
1372
1373config HAVE_PCSPKR_PLATFORM
1374 bool
1375
1376
1377config BPF
1378 bool
1379
1380menuconfig EXPERT
1381 bool "Configure standard kernel features (expert users)"
1382
1383 select DEBUG_KERNEL
1384 help
1385 This option allows certain base kernel options and settings
1386 to be disabled or tweaked. This is for specialized
1387 environments which can tolerate a "non-standard" kernel.
1388 Only use this if you really know what you are doing.
1389
1390config UID16
1391 bool "Enable 16-bit UID system calls" if EXPERT
1392 depends on HAVE_UID16 && MULTIUSER
1393 default y
1394 help
1395 This enables the legacy 16-bit UID syscall wrappers.
1396
1397config MULTIUSER
1398 bool "Multiple users, groups and capabilities support" if EXPERT
1399 default y
1400 help
1401 This option enables support for non-root users, groups and
1402 capabilities.
1403
1404 If you say N here, all processes will run with UID 0, GID 0, and all
1405 possible capabilities. Saying N here also compiles out support for
1406 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1407 setgid, and capset.
1408
1409 If unsure, say Y here.
1410
1411config SGETMASK_SYSCALL
1412 bool "sgetmask/ssetmask syscalls support" if EXPERT
1413 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1414 ---help---
1415 sys_sgetmask and sys_ssetmask are obsolete system calls
1416 no longer supported in libc but still enabled by default in some
1417 architectures.
1418
1419 If unsure, leave the default option here.
1420
1421config SYSFS_SYSCALL
1422 bool "Sysfs syscall support" if EXPERT
1423 default y
1424 ---help---
1425 sys_sysfs is an obsolete system call no longer supported in libc.
1426 Note that disabling this option is more secure but might break
1427 compatibility with some systems.
1428
1429 If unsure say Y here.
1430
1431config SYSCTL_SYSCALL
1432 bool "Sysctl syscall support" if EXPERT
1433 depends on PROC_SYSCTL
1434 default n
1435 select SYSCTL
1436 ---help---
1437 sys_sysctl uses binary paths that have been found challenging
1438 to properly maintain and use. The interface in /proc/sys
1439 using paths with ascii names is now the primary path to this
1440 information.
1441
1442 Almost nothing using the binary sysctl interface so if you are
1443 trying to save some space it is probably safe to disable this,
1444 making your kernel marginally smaller.
1445
1446 If unsure say N here.
1447
1448config KALLSYMS
1449 bool "Load all symbols for debugging/ksymoops" if EXPERT
1450 default y
1451 help
1452 Say Y here to let the kernel print out symbolic crash information and
1453 symbolic stack backtraces. This increases the size of the kernel
1454 somewhat, as all symbols have to be loaded into the kernel image.
1455
1456config KALLSYMS_ALL
1457 bool "Include all symbols in kallsyms"
1458 depends on DEBUG_KERNEL && KALLSYMS
1459 help
1460 Normally kallsyms only contains the symbols of functions for nicer
1461 OOPS messages and backtraces (i.e., symbols from the text and inittext
1462 sections). This is sufficient for most cases. And only in very rare
1463 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1464 names of variables from the data sections, etc).
1465
1466 This option makes sure that all symbols are loaded into the kernel
1467 image (i.e., symbols from all sections) in cost of increased kernel
1468 size (depending on the kernel configuration, it may be 300KiB or
1469 something like this).
1470
1471 Say N unless you really need all symbols.
1472
1473config KALLSYMS_ABSOLUTE_PERCPU
1474 bool
1475 depends on KALLSYMS
1476 default X86_64 && SMP
1477
1478config KALLSYMS_BASE_RELATIVE
1479 bool
1480 depends on KALLSYMS
1481 default !IA64 && !(TILE && 64BIT)
1482 help
1483 Instead of emitting them as absolute values in the native word size,
1484 emit the symbol references in the kallsyms table as 32-bit entries,
1485 each containing a relative value in the range [base, base + U32_MAX]
1486 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1487 an absolute value in the range [0, S32_MAX] or a relative value in the
1488 range [base, base + S32_MAX], where base is the lowest relative symbol
1489 address encountered in the image.
1490
1491 On 64-bit builds, this reduces the size of the address table by 50%,
1492 but more importantly, it results in entries whose values are build
1493 time constants, and no relocation pass is required at runtime to fix
1494 up the entries based on the runtime load address of the kernel.
1495
1496config PRINTK
1497 default y
1498 bool "Enable support for printk" if EXPERT
1499 select IRQ_WORK
1500 help
1501 This option enables normal printk support. Removing it
1502 eliminates most of the message strings from the kernel image
1503 and makes the kernel more or less silent. As this makes it
1504 very difficult to diagnose system problems, saying N here is
1505 strongly discouraged.
1506
1507config PRINTK_NMI
1508 def_bool y
1509 depends on PRINTK
1510 depends on HAVE_NMI
1511
1512config BUG
1513 bool "BUG() support" if EXPERT
1514 default y
1515 help
1516 Disabling this option eliminates support for BUG and WARN, reducing
1517 the size of your kernel image and potentially quietly ignoring
1518 numerous fatal conditions. You should only consider disabling this
1519 option for embedded systems with no facilities for reporting errors.
1520 Just say Y.
1521
1522config ELF_CORE
1523 depends on COREDUMP
1524 default y
1525 bool "Enable ELF core dumps" if EXPERT
1526 help
1527 Enable support for generating core dumps. Disabling saves about 4k.
1528
1529
1530config PCSPKR_PLATFORM
1531 bool "Enable PC-Speaker support" if EXPERT
1532 depends on HAVE_PCSPKR_PLATFORM
1533 select I8253_LOCK
1534 default y
1535 help
1536 This option allows to disable the internal PC-Speaker
1537 support, saving some memory.
1538
1539config BASE_FULL
1540 default y
1541 bool "Enable full-sized data structures for core" if EXPERT
1542 help
1543 Disabling this option reduces the size of miscellaneous core
1544 kernel data structures. This saves memory on small machines,
1545 but may reduce performance.
1546
1547config FUTEX
1548 bool "Enable futex support" if EXPERT
1549 default y
1550 select RT_MUTEXES
1551 help
1552 Disabling this option will cause the kernel to be built without
1553 support for "fast userspace mutexes". The resulting kernel may not
1554 run glibc-based applications correctly.
1555
1556config HAVE_FUTEX_CMPXCHG
1557 bool
1558 depends on FUTEX
1559 help
1560 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1561 is implemented and always working. This removes a couple of runtime
1562 checks.
1563
1564config EPOLL
1565 bool "Enable eventpoll support" if EXPERT
1566 default y
1567 select ANON_INODES
1568 help
1569 Disabling this option will cause the kernel to be built without
1570 support for epoll family of system calls.
1571
1572config SIGNALFD
1573 bool "Enable signalfd() system call" if EXPERT
1574 select ANON_INODES
1575 default y
1576 help
1577 Enable the signalfd() system call that allows to receive signals
1578 on a file descriptor.
1579
1580 If unsure, say Y.
1581
1582config TIMERFD
1583 bool "Enable timerfd() system call" if EXPERT
1584 select ANON_INODES
1585 default y
1586 help
1587 Enable the timerfd() system call that allows to receive timer
1588 events on a file descriptor.
1589
1590 If unsure, say Y.
1591
1592config EVENTFD
1593 bool "Enable eventfd() system call" if EXPERT
1594 select ANON_INODES
1595 default y
1596 help
1597 Enable the eventfd() system call that allows to receive both
1598 kernel notification (ie. KAIO) or userspace notifications.
1599
1600 If unsure, say Y.
1601
1602
1603config BPF_SYSCALL
1604 bool "Enable bpf() system call"
1605 select ANON_INODES
1606 select BPF
1607 default n
1608 help
1609 Enable the bpf() system call that allows to manipulate eBPF
1610 programs and maps via file descriptors.
1611
1612config SHMEM
1613 bool "Use full shmem filesystem" if EXPERT
1614 default y
1615 depends on MMU
1616 help
1617 The shmem is an internal filesystem used to manage shared memory.
1618 It is backed by swap and manages resource limits. It is also exported
1619 to userspace as tmpfs if TMPFS is enabled. Disabling this
1620 option replaces shmem and tmpfs with the much simpler ramfs code,
1621 which may be appropriate on small systems without swap.
1622
1623config AIO
1624 bool "Enable AIO support" if EXPERT
1625 default y
1626 help
1627 This option enables POSIX asynchronous I/O which may by used
1628 by some high performance threaded applications. Disabling
1629 this option saves about 7k.
1630
1631config ADVISE_SYSCALLS
1632 bool "Enable madvise/fadvise syscalls" if EXPERT
1633 default y
1634 help
1635 This option enables the madvise and fadvise syscalls, used by
1636 applications to advise the kernel about their future memory or file
1637 usage, improving performance. If building an embedded system where no
1638 applications use these syscalls, you can disable this option to save
1639 space.
1640
1641config USERFAULTFD
1642 bool "Enable userfaultfd() system call"
1643 select ANON_INODES
1644 depends on MMU
1645 help
1646 Enable the userfaultfd() system call that allows to intercept and
1647 handle page faults in userland.
1648
1649config PCI_QUIRKS
1650 default y
1651 bool "Enable PCI quirk workarounds" if EXPERT
1652 depends on PCI
1653 help
1654 This enables workarounds for various PCI chipset
1655 bugs/quirks. Disable this only if your target machine is
1656 unaffected by PCI quirks.
1657
1658config MEMBARRIER
1659 bool "Enable membarrier() system call" if EXPERT
1660 default y
1661 help
1662 Enable the membarrier() system call that allows issuing memory
1663 barriers across all running threads, which can be used to distribute
1664 the cost of user-space memory barriers asymmetrically by transforming
1665 pairs of memory barriers into pairs consisting of membarrier() and a
1666 compiler barrier.
1667
1668 If unsure, say Y.
1669
1670config EMBEDDED
1671 bool "Embedded system"
1672 option allnoconfig_y
1673 select EXPERT
1674 help
1675 This option should be enabled if compiling the kernel for
1676 an embedded system so certain expert options are available
1677 for configuration.
1678
1679config HAVE_PERF_EVENTS
1680 bool
1681 help
1682 See tools/perf/design.txt for details.
1683
1684config PERF_USE_VMALLOC
1685 bool
1686 help
1687 See tools/perf/design.txt for details
1688
1689menu "Kernel Performance Events And Counters"
1690
1691config PERF_EVENTS
1692 bool "Kernel performance events and counters"
1693 default y if PROFILING
1694 depends on HAVE_PERF_EVENTS
1695 select ANON_INODES
1696 select IRQ_WORK
1697 select SRCU
1698 help
1699 Enable kernel support for various performance events provided
1700 by software and hardware.
1701
1702 Software events are supported either built-in or via the
1703 use of generic tracepoints.
1704
1705 Most modern CPUs support performance events via performance
1706 counter registers. These registers count the number of certain
1707 types of hw events: such as instructions executed, cachemisses
1708 suffered, or branches mis-predicted - without slowing down the
1709 kernel or applications. These registers can also trigger interrupts
1710 when a threshold number of events have passed - and can thus be
1711 used to profile the code that runs on that CPU.
1712
1713 The Linux Performance Event subsystem provides an abstraction of
1714 these software and hardware event capabilities, available via a
1715 system call and used by the "perf" utility in tools/perf/. It
1716 provides per task and per CPU counters, and it provides event
1717 capabilities on top of those.
1718
1719 Say Y if unsure.
1720
1721config DEBUG_PERF_USE_VMALLOC
1722 default n
1723 bool "Debug: use vmalloc to back perf mmap() buffers"
1724 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1725 select PERF_USE_VMALLOC
1726 help
1727 Use vmalloc memory to back perf mmap() buffers.
1728
1729 Mostly useful for debugging the vmalloc code on platforms
1730 that don't require it.
1731
1732 Say N if unsure.
1733
1734endmenu
1735
1736config VM_EVENT_COUNTERS
1737 default y
1738 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1739 help
1740 VM event counters are needed for event counts to be shown.
1741 This option allows the disabling of the VM event counters
1742 on EXPERT systems. /proc/vmstat will only show page counts
1743 if VM event counters are disabled.
1744
1745config SLUB_DEBUG
1746 default y
1747 bool "Enable SLUB debugging support" if EXPERT
1748 depends on SLUB && SYSFS
1749 help
1750 SLUB has extensive debug support features. Disabling these can
1751 result in significant savings in code size. This also disables
1752 SLUB sysfs support. /sys/slab will not exist and there will be
1753 no support for cache validation etc.
1754
1755config COMPAT_BRK
1756 bool "Disable heap randomization"
1757 default y
1758 help
1759 Randomizing heap placement makes heap exploits harder, but it
1760 also breaks ancient binaries (including anything libc5 based).
1761 This option changes the bootup default to heap randomization
1762 disabled, and can be overridden at runtime by setting
1763 /proc/sys/kernel/randomize_va_space to 2.
1764
1765 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1766
1767choice
1768 prompt "Choose SLAB allocator"
1769 default SLUB
1770 help
1771 This option allows to select a slab allocator.
1772
1773config SLAB
1774 bool "SLAB"
1775 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1776 help
1777 The regular slab allocator that is established and known to work
1778 well in all environments. It organizes cache hot objects in
1779 per cpu and per node queues.
1780
1781config SLUB
1782 bool "SLUB (Unqueued Allocator)"
1783 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1784 help
1785 SLUB is a slab allocator that minimizes cache line usage
1786 instead of managing queues of cached objects (SLAB approach).
1787 Per cpu caching is realized using slabs of objects instead
1788 of queues of objects. SLUB can use memory efficiently
1789 and has enhanced diagnostics. SLUB is the default choice for
1790 a slab allocator.
1791
1792config SLOB
1793 depends on EXPERT
1794 bool "SLOB (Simple Allocator)"
1795 help
1796 SLOB replaces the stock allocator with a drastically simpler
1797 allocator. SLOB is generally more space efficient but
1798 does not perform as well on large systems.
1799
1800endchoice
1801
1802config SLAB_FREELIST_RANDOM
1803 default n
1804 depends on SLAB || SLUB
1805 bool "SLAB freelist randomization"
1806 help
1807 Randomizes the freelist order used on creating new pages. This
1808 security feature reduces the predictability of the kernel slab
1809 allocator against heap overflows.
1810
1811config SLUB_CPU_PARTIAL
1812 default y
1813 depends on SLUB && SMP
1814 bool "SLUB per cpu partial cache"
1815 help
1816 Per cpu partial caches accellerate objects allocation and freeing
1817 that is local to a processor at the price of more indeterminism
1818 in the latency of the free. On overflow these caches will be cleared
1819 which requires the taking of locks that may cause latency spikes.
1820 Typically one would choose no for a realtime system.
1821
1822config MMAP_ALLOW_UNINITIALIZED
1823 bool "Allow mmapped anonymous memory to be uninitialized"
1824 depends on EXPERT && !MMU
1825 default n
1826 help
1827 Normally, and according to the Linux spec, anonymous memory obtained
1828 from mmap() has it's contents cleared before it is passed to
1829 userspace. Enabling this config option allows you to request that
1830 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1831 providing a huge performance boost. If this option is not enabled,
1832 then the flag will be ignored.
1833
1834 This is taken advantage of by uClibc's malloc(), and also by
1835 ELF-FDPIC binfmt's brk and stack allocator.
1836
1837 Because of the obvious security issues, this option should only be
1838 enabled on embedded devices where you control what is run in
1839 userspace. Since that isn't generally a problem on no-MMU systems,
1840 it is normally safe to say Y here.
1841
1842 See Documentation/nommu-mmap.txt for more information.
1843
1844config SYSTEM_DATA_VERIFICATION
1845 def_bool n
1846 select SYSTEM_TRUSTED_KEYRING
1847 select KEYS
1848 select CRYPTO
1849 select CRYPTO_RSA
1850 select ASYMMETRIC_KEY_TYPE
1851 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1852 select ASN1
1853 select OID_REGISTRY
1854 select X509_CERTIFICATE_PARSER
1855 select PKCS7_MESSAGE_PARSER
1856 help
1857 Provide PKCS#7 message verification using the contents of the system
1858 trusted keyring to provide public keys. This then can be used for
1859 module verification, kexec image verification and firmware blob
1860 verification.
1861
1862config PROFILING
1863 bool "Profiling support"
1864 help
1865 Say Y here to enable the extended profiling support mechanisms used
1866 by profilers such as OProfile.
1867
1868
1869
1870
1871
1872config TRACEPOINTS
1873 bool
1874
1875source "arch/Kconfig"
1876
1877endmenu
1878
1879config HAVE_GENERIC_DMA_COHERENT
1880 bool
1881 default n
1882
1883config SLABINFO
1884 bool
1885 depends on PROC_FS
1886 depends on SLAB || SLUB_DEBUG
1887 default y
1888
1889config RT_MUTEXES
1890 bool
1891
1892config BASE_SMALL
1893 int
1894 default 0 if BASE_FULL
1895 default 1 if !BASE_FULL
1896
1897menuconfig MODULES
1898 bool "Enable loadable module support"
1899 option modules
1900 help
1901 Kernel modules are small pieces of compiled code which can
1902 be inserted in the running kernel, rather than being
1903 permanently built into the kernel. You use the "modprobe"
1904 tool to add (and sometimes remove) them. If you say Y here,
1905 many parts of the kernel can be built as modules (by
1906 answering M instead of Y where indicated): this is most
1907 useful for infrequently used options which are not required
1908 for booting. For more information, see the man pages for
1909 modprobe, lsmod, modinfo, insmod and rmmod.
1910
1911 If you say Y here, you will need to run "make
1912 modules_install" to put the modules under /lib/modules/
1913 where modprobe can find them (you may need to be root to do
1914 this).
1915
1916 If unsure, say Y.
1917
1918if MODULES
1919
1920config MODULE_FORCE_LOAD
1921 bool "Forced module loading"
1922 default n
1923 help
1924 Allow loading of modules without version information (ie. modprobe
1925 --force). Forced module loading sets the 'F' (forced) taint flag and
1926 is usually a really bad idea.
1927
1928config MODULE_UNLOAD
1929 bool "Module unloading"
1930 help
1931 Without this option you will not be able to unload any
1932 modules (note that some modules may not be unloadable
1933 anyway), which makes your kernel smaller, faster
1934 and simpler. If unsure, say Y.
1935
1936config MODULE_FORCE_UNLOAD
1937 bool "Forced module unloading"
1938 depends on MODULE_UNLOAD
1939 help
1940 This option allows you to force a module to unload, even if the
1941 kernel believes it is unsafe: the kernel will remove the module
1942 without waiting for anyone to stop using it (using the -f option to
1943 rmmod). This is mainly for kernel developers and desperate users.
1944 If unsure, say N.
1945
1946config MODVERSIONS
1947 bool "Module versioning support"
1948 help
1949 Usually, you have to use modules compiled with your kernel.
1950 Saying Y here makes it sometimes possible to use modules
1951 compiled for different kernels, by adding enough information
1952 to the modules to (hopefully) spot any changes which would
1953 make them incompatible with the kernel you are running. If
1954 unsure, say N.
1955
1956config MODULE_SRCVERSION_ALL
1957 bool "Source checksum for all modules"
1958 help
1959 Modules which contain a MODULE_VERSION get an extra "srcversion"
1960 field inserted into their modinfo section, which contains a
1961 sum of the source files which made it. This helps maintainers
1962 see exactly which source was used to build a module (since
1963 others sometimes change the module source without updating
1964 the version). With this option, such a "srcversion" field
1965 will be created for all modules. If unsure, say N.
1966
1967config MODULE_SIG
1968 bool "Module signature verification"
1969 depends on MODULES
1970 select SYSTEM_DATA_VERIFICATION
1971 help
1972 Check modules for valid signatures upon load: the signature
1973 is simply appended to the module. For more information see
1974 Documentation/module-signing.txt.
1975
1976 Note that this option adds the OpenSSL development packages as a
1977 kernel build dependency so that the signing tool can use its crypto
1978 library.
1979
1980 !!!WARNING!!! If you enable this option, you MUST make sure that the
1981 module DOES NOT get stripped after being signed. This includes the
1982 debuginfo strip done by some packagers (such as rpmbuild) and
1983 inclusion into an initramfs that wants the module size reduced.
1984
1985config MODULE_SIG_FORCE
1986 bool "Require modules to be validly signed"
1987 depends on MODULE_SIG
1988 help
1989 Reject unsigned modules or signed modules for which we don't have a
1990 key. Without this, such modules will simply taint the kernel.
1991
1992config MODULE_SIG_ALL
1993 bool "Automatically sign all modules"
1994 default y
1995 depends on MODULE_SIG
1996 help
1997 Sign all modules during make modules_install. Without this option,
1998 modules must be signed manually, using the scripts/sign-file tool.
1999
2000comment "Do not forget to sign required modules with scripts/sign-file"
2001 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2002
2003choice
2004 prompt "Which hash algorithm should modules be signed with?"
2005 depends on MODULE_SIG
2006 help
2007 This determines which sort of hashing algorithm will be used during
2008 signature generation. This algorithm _must_ be built into the kernel
2009 directly so that signature verification can take place. It is not
2010 possible to load a signed module containing the algorithm to check
2011 the signature on that module.
2012
2013config MODULE_SIG_SHA1
2014 bool "Sign modules with SHA-1"
2015 select CRYPTO_SHA1
2016
2017config MODULE_SIG_SHA224
2018 bool "Sign modules with SHA-224"
2019 select CRYPTO_SHA256
2020
2021config MODULE_SIG_SHA256
2022 bool "Sign modules with SHA-256"
2023 select CRYPTO_SHA256
2024
2025config MODULE_SIG_SHA384
2026 bool "Sign modules with SHA-384"
2027 select CRYPTO_SHA512
2028
2029config MODULE_SIG_SHA512
2030 bool "Sign modules with SHA-512"
2031 select CRYPTO_SHA512
2032
2033endchoice
2034
2035config MODULE_SIG_HASH
2036 string
2037 depends on MODULE_SIG
2038 default "sha1" if MODULE_SIG_SHA1
2039 default "sha224" if MODULE_SIG_SHA224
2040 default "sha256" if MODULE_SIG_SHA256
2041 default "sha384" if MODULE_SIG_SHA384
2042 default "sha512" if MODULE_SIG_SHA512
2043
2044config MODULE_COMPRESS
2045 bool "Compress modules on installation"
2046 depends on MODULES
2047 help
2048
2049 Compresses kernel modules when 'make modules_install' is run; gzip or
2050 xz depending on "Compression algorithm" below.
2051
2052 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2053
2054 Out-of-tree kernel modules installed using Kbuild will also be
2055 compressed upon installation.
2056
2057 Note: for modules inside an initrd or initramfs, it's more efficient
2058 to compress the whole initrd or initramfs instead.
2059
2060 Note: This is fully compatible with signed modules.
2061
2062 If in doubt, say N.
2063
2064choice
2065 prompt "Compression algorithm"
2066 depends on MODULE_COMPRESS
2067 default MODULE_COMPRESS_GZIP
2068 help
2069 This determines which sort of compression will be used during
2070 'make modules_install'.
2071
2072 GZIP (default) and XZ are supported.
2073
2074config MODULE_COMPRESS_GZIP
2075 bool "GZIP"
2076
2077config MODULE_COMPRESS_XZ
2078 bool "XZ"
2079
2080endchoice
2081
2082config TRIM_UNUSED_KSYMS
2083 bool "Trim unused exported kernel symbols"
2084 depends on MODULES && !UNUSED_SYMBOLS
2085 help
2086 The kernel and some modules make many symbols available for
2087 other modules to use via EXPORT_SYMBOL() and variants. Depending
2088 on the set of modules being selected in your kernel configuration,
2089 many of those exported symbols might never be used.
2090
2091 This option allows for unused exported symbols to be dropped from
2092 the build. In turn, this provides the compiler more opportunities
2093 (especially when using LTO) for optimizing the code and reducing
2094 binary size. This might have some security advantages as well.
2095
2096 If unsure, or if you need to build out-of-tree modules, say N.
2097
2098endif
2099
2100config MODULES_TREE_LOOKUP
2101 def_bool y
2102 depends on PERF_EVENTS || TRACING
2103
2104config INIT_ALL_POSSIBLE
2105 bool
2106 help
2107 Back when each arch used to define their own cpu_online_mask and
2108 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2109 with all 1s, and others with all 0s. When they were centralised,
2110 it was better to provide this option than to break all the archs
2111 and have several arch maintainers pursuing me down dark alleys.
2112
2113source "block/Kconfig"
2114
2115config PREEMPT_NOTIFIERS
2116 bool
2117
2118config PADATA
2119 depends on SMP
2120 bool
2121
2122config ASN1
2123 tristate
2124 help
2125 Build a simple ASN.1 grammar compiler that produces a bytecode output
2126 that can be interpreted by the ASN.1 stream decoder and used to
2127 inform it as to what tags are to be expected in a stream and what
2128 functions to call on what tags.
2129
2130source "kernel/Kconfig.locks"
2131
