| blob | af09b4fb43d291856708eb78197adb74dd1b4f48 |
1 config ARCH
2 string
3 option env="ARCH"
5 config KERNELVERSION
6 string
7 option env="KERNELVERSION"
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"
19 config CONSTRUCTORS
20 bool
21 depends on !UML
23 config IRQ_WORK
24 bool
26 config BUILDTIME_EXTABLE_SORT
27 bool
29 menu "General setup"
31 config BROKEN
32 bool
34 config BROKEN_ON_SMP
35 bool
36 depends on BROKEN || !SMP
37 default y
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.
48 config CROSS_COMPILE
49 string "Cross-compiler tool prefix"
50 help
51 Same as running 'make CROSS_COMPILE=prefix-' but stored for
52 default make runs in this kernel build directory. You don't
53 need to set this unless you want the configured kernel build
54 directory to select the cross-compiler automatically.
56 config COMPILE_TEST
57 bool "Compile also drivers which will not load"
58 default n
59 help
60 Some drivers can be compiled on a different platform than they are
61 intended to be run on. Despite they cannot be loaded there (or even
62 when they load they cannot be used due to missing HW support),
63 developers still, opposing to distributors, might want to build such
64 drivers to compile-test them.
66 If you are a developer and want to build everything available, say Y
67 here. If you are a user/distributor, say N here to exclude useless
68 drivers to be distributed.
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.
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.
88 A string of the format -gxxxxxxxx will be added to the localversion
89 if a git-based tree is found. The string generated by this will be
90 appended after any matching localversion* files, and after the value
91 set in CONFIG_LOCALVERSION.
93 (The actual string used here is the first eight characters produced
94 by running the command:
96 $ git rev-parse --verify HEAD
98 which is done within the script "scripts/setlocalversion".)
100 config HAVE_KERNEL_GZIP
101 bool
103 config HAVE_KERNEL_BZIP2
104 bool
106 config HAVE_KERNEL_LZMA
107 bool
109 config HAVE_KERNEL_XZ
110 bool
112 config HAVE_KERNEL_LZO
113 bool
115 config HAVE_KERNEL_LZ4
116 bool
118 choice
119 prompt "Kernel compression mode"
120 default KERNEL_GZIP
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.
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)
134 High compression options are mostly useful for users, who
135 are low on disk space (embedded systems), but for whom ram
136 size matters less.
138 If in doubt, select 'gzip'
140 config KERNEL_GZIP
141 bool "Gzip"
142 depends on HAVE_KERNEL_GZIP
143 help
144 The old and tried gzip compression. It provides a good balance
145 between compression ratio and decompression speed.
147 config KERNEL_BZIP2
148 bool "Bzip2"
149 depends on HAVE_KERNEL_BZIP2
150 help
151 Its compression ratio and speed is intermediate.
152 Decompression speed is slowest among the choices. The kernel
153 size is about 10% smaller with bzip2, in comparison to gzip.
154 Bzip2 uses a large amount of memory. For modern kernels you
155 will need at least 8MB RAM or more for booting.
157 config KERNEL_LZMA
158 bool "LZMA"
159 depends on HAVE_KERNEL_LZMA
160 help
161 This compression algorithm's ratio is best. Decompression speed
162 is between gzip and bzip2. Compression is slowest.
163 The kernel size is about 33% smaller with LZMA in comparison to gzip.
165 config KERNEL_XZ
166 bool "XZ"
167 depends on HAVE_KERNEL_XZ
168 help
169 XZ uses the LZMA2 algorithm and instruction set specific
170 BCJ filters which can improve compression ratio of executable
171 code. The size of the kernel is about 30% smaller with XZ in
172 comparison to gzip. On architectures for which there is a BCJ
173 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
174 will create a few percent smaller kernel than plain LZMA.
176 The speed is about the same as with LZMA: The decompression
177 speed of XZ is better than that of bzip2 but worse than gzip
178 and LZO. Compression is slow.
180 config KERNEL_LZO
181 bool "LZO"
182 depends on HAVE_KERNEL_LZO
183 help
184 Its compression ratio is the poorest among the choices. The kernel
185 size is about 10% bigger than gzip; however its speed
186 (both compression and decompression) is the fastest.
188 config KERNEL_LZ4
189 bool "LZ4"
190 depends on HAVE_KERNEL_LZ4
191 help
192 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
193 A preliminary version of LZ4 de/compression tool is available at
194 <https://code.google.com/p/lz4/>.
196 Its compression ratio is worse than LZO. The size of the kernel
197 is about 8% bigger than LZO. But the decompression speed is
198 faster than LZO.
200 endchoice
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.
211 config SWAP
212 bool "Support for paging of anonymous memory (swap)"
213 depends on MMU && BLOCK
214 default y
215 help
216 This option allows you to choose whether you want to have support
217 for so called swap devices or swap files in your kernel that are
218 used to provide more virtual memory than the actual RAM present
219 in your computer. If unsure say Y.
221 config SYSVIPC
222 bool "System V IPC"
223 ---help---
224 Inter Process Communication is a suite of library functions and
225 system calls which let processes (running programs) synchronize and
226 exchange information. It is generally considered to be a good thing,
227 and some programs won't run unless you say Y here. In particular, if
228 you want to run the DOS emulator dosemu under Linux (read the
229 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
230 you'll need to say Y here.
232 You can find documentation about IPC with "info ipc" and also in
233 section 6.4 of the Linux Programmer's Guide, available from
234 <http://www.tldp.org/guides.html>.
236 config SYSVIPC_SYSCTL
237 bool
238 depends on SYSVIPC
239 depends on SYSCTL
240 default y
242 config POSIX_MQUEUE
243 bool "POSIX Message Queues"
244 depends on NET
245 ---help---
246 POSIX variant of message queues is a part of IPC. In POSIX message
247 queues every message has a priority which decides about succession
248 of receiving it by a process. If you want to compile and run
249 programs written e.g. for Solaris with use of its POSIX message
250 queues (functions mq_*) say Y here.
252 POSIX message queues are visible as a filesystem called 'mqueue'
253 and can be mounted somewhere if you want to do filesystem
254 operations on message queues.
256 If unsure, say Y.
258 config POSIX_MQUEUE_SYSCTL
259 bool
260 depends on POSIX_MQUEUE
261 depends on SYSCTL
262 default y
264 config CROSS_MEMORY_ATTACH
265 bool "Enable process_vm_readv/writev syscalls"
266 depends on MMU
267 default y
268 help
269 Enabling this option adds the system calls process_vm_readv and
270 process_vm_writev which allow a process with the correct privileges
271 to directly read from or write to another process' address space.
272 See the man page for more details.
274 config FHANDLE
275 bool "open by fhandle syscalls"
276 select EXPORTFS
277 help
278 If you say Y here, a user level program will be able to map
279 file names to handle and then later use the handle for
280 different file system operations. This is useful in implementing
281 userspace file servers, which now track files using handles instead
282 of names. The handle would remain the same even if file names
283 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
284 syscalls.
286 config USELIB
287 bool "uselib syscall"
288 default y
289 help
290 This option enables the uselib syscall, a system call used in the
291 dynamic linker from libc5 and earlier. glibc does not use this
292 system call. If you intend to run programs built on libc5 or
293 earlier, you may need to enable this syscall. Current systems
294 running glibc can safely disable this.
296 config AUDIT
297 bool "Auditing support"
298 depends on NET
299 help
300 Enable auditing infrastructure that can be used with another
301 kernel subsystem, such as SELinux (which requires this for
302 logging of avc messages output). Does not do system-call
303 auditing without CONFIG_AUDITSYSCALL.
305 config HAVE_ARCH_AUDITSYSCALL
306 bool
308 config AUDITSYSCALL
309 bool "Enable system-call auditing support"
310 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
311 default y if SECURITY_SELINUX
312 help
313 Enable low-overhead system-call auditing infrastructure that
314 can be used independently or with another kernel subsystem,
315 such as SELinux.
317 config AUDIT_WATCH
318 def_bool y
319 depends on AUDITSYSCALL
320 select FSNOTIFY
322 config AUDIT_TREE
323 def_bool y
324 depends on AUDITSYSCALL
325 select FSNOTIFY
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
330 menu "CPU/Task time and stats accounting"
332 config VIRT_CPU_ACCOUNTING
333 bool
335 choice
336 prompt "Cputime accounting"
337 default TICK_CPU_ACCOUNTING if !PPC64
338 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
340 # Kind of a stub config for the pure tick based cputime accounting
341 config TICK_CPU_ACCOUNTING
342 bool "Simple tick based cputime accounting"
343 depends on !S390 && !NO_HZ_FULL
344 help
345 This is the basic tick based cputime accounting that maintains
346 statistics about user, system and idle time spent on per jiffies
347 granularity.
349 If unsure, say Y.
351 config VIRT_CPU_ACCOUNTING_NATIVE
352 bool "Deterministic task and CPU time accounting"
353 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
354 select VIRT_CPU_ACCOUNTING
355 help
356 Select this option to enable more accurate task and CPU time
357 accounting. This is done by reading a CPU counter on each
358 kernel entry and exit and on transitions within the kernel
359 between system, softirq and hardirq state, so there is a
360 small performance impact. In the case of s390 or IBM POWER > 5,
361 this also enables accounting of stolen time on logically-partitioned
362 systems.
364 config VIRT_CPU_ACCOUNTING_GEN
365 bool "Full dynticks CPU time accounting"
366 depends on HAVE_CONTEXT_TRACKING
367 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
368 select VIRT_CPU_ACCOUNTING
369 select CONTEXT_TRACKING
370 help
371 Select this option to enable task and CPU time accounting on full
372 dynticks systems. This accounting is implemented by watching every
373 kernel-user boundaries using the context tracking subsystem.
374 The accounting is thus performed at the expense of some significant
375 overhead.
377 For now this is only useful if you are working on the full
378 dynticks subsystem development.
380 If unsure, say N.
382 config IRQ_TIME_ACCOUNTING
383 bool "Fine granularity task level IRQ time accounting"
384 depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
385 help
386 Select this option to enable fine granularity task irq time
387 accounting. This is done by reading a timestamp on each
388 transitions between softirq and hardirq state, so there can be a
389 small performance impact.
391 If in doubt, say N here.
393 endchoice
395 config BSD_PROCESS_ACCT
396 bool "BSD Process Accounting"
397 depends on MULTIUSER
398 help
399 If you say Y here, a user level program will be able to instruct the
400 kernel (via a special system call) to write process accounting
401 information to a file: whenever a process exits, information about
402 that process will be appended to the file by the kernel. The
403 information includes things such as creation time, owning user,
404 command name, memory usage, controlling terminal etc. (the complete
405 list is in the struct acct in <file:include/linux/acct.h>). It is
406 up to the user level program to do useful things with this
407 information. This is generally a good idea, so say Y.
409 config BSD_PROCESS_ACCT_V3
410 bool "BSD Process Accounting version 3 file format"
411 depends on BSD_PROCESS_ACCT
412 default n
413 help
414 If you say Y here, the process accounting information is written
415 in a new file format that also logs the process IDs of each
416 process and it's parent. Note that this file format is incompatible
417 with previous v0/v1/v2 file formats, so you will need updated tools
418 for processing it. A preliminary version of these tools is available
419 at <http://www.gnu.org/software/acct/>.
421 config TASKSTATS
422 bool "Export task/process statistics through netlink"
423 depends on NET
424 depends on MULTIUSER
425 default n
426 help
427 Export selected statistics for tasks/processes through the
428 generic netlink interface. Unlike BSD process accounting, the
429 statistics are available during the lifetime of tasks/processes as
430 responses to commands. Like BSD accounting, they are sent to user
431 space on task exit.
433 Say N if unsure.
435 config TASK_DELAY_ACCT
436 bool "Enable per-task delay accounting"
437 depends on TASKSTATS
438 select SCHED_INFO
439 help
440 Collect information on time spent by a task waiting for system
441 resources like cpu, synchronous block I/O completion and swapping
442 in pages. Such statistics can help in setting a task's priorities
443 relative to other tasks for cpu, io, rss limits etc.
445 Say N if unsure.
447 config TASK_XACCT
448 bool "Enable extended accounting over taskstats"
449 depends on TASKSTATS
450 help
451 Collect extended task accounting data and send the data
452 to userland for processing over the taskstats interface.
454 Say N if unsure.
456 config TASK_IO_ACCOUNTING
457 bool "Enable per-task storage I/O accounting"
458 depends on TASK_XACCT
459 help
460 Collect information on the number of bytes of storage I/O which this
461 task has caused.
463 Say N if unsure.
465 endmenu # "CPU/Task time and stats accounting"
467 menu "RCU Subsystem"
469 config TREE_RCU
470 bool
471 default y if !PREEMPT && SMP
472 help
473 This option selects the RCU implementation that is
474 designed for very large SMP system with hundreds or
475 thousands of CPUs. It also scales down nicely to
476 smaller systems.
478 config PREEMPT_RCU
479 bool
480 default y if PREEMPT
481 help
482 This option selects the RCU implementation that is
483 designed for very large SMP systems with hundreds or
484 thousands of CPUs, but for which real-time response
485 is also required. It also scales down nicely to
486 smaller systems.
488 Select this option if you are unsure.
490 config TINY_RCU
491 bool
492 default y if !PREEMPT && !SMP
493 help
494 This option selects the RCU implementation that is
495 designed for UP systems from which real-time response
496 is not required. This option greatly reduces the
497 memory footprint of RCU.
499 config RCU_EXPERT
500 bool "Make expert-level adjustments to RCU configuration"
501 default n
502 help
503 This option needs to be enabled if you wish to make
504 expert-level adjustments to RCU configuration. By default,
505 no such adjustments can be made, which has the often-beneficial
506 side-effect of preventing "make oldconfig" from asking you all
507 sorts of detailed questions about how you would like numerous
508 obscure RCU options to be set up.
510 Say Y if you need to make expert-level adjustments to RCU.
512 Say N if you are unsure.
514 config SRCU
515 bool
516 help
517 This option selects the sleepable version of RCU. This version
518 permits arbitrary sleeping or blocking within RCU read-side critical
519 sections.
521 config TASKS_RCU
522 bool
523 default n
524 select SRCU
525 help
526 This option enables a task-based RCU implementation that uses
527 only voluntary context switch (not preemption!), idle, and
528 user-mode execution as quiescent states.
530 config RCU_STALL_COMMON
531 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
532 help
533 This option enables RCU CPU stall code that is common between
534 the TINY and TREE variants of RCU. The purpose is to allow
535 the tiny variants to disable RCU CPU stall warnings, while
536 making these warnings mandatory for the tree variants.
538 config CONTEXT_TRACKING
539 bool
541 config RCU_USER_QS
542 bool
543 help
544 This option sets hooks on kernel / userspace boundaries and
545 puts RCU in extended quiescent state when the CPU runs in
546 userspace. It means that when a CPU runs in userspace, it is
547 excluded from the global RCU state machine and thus doesn't
548 try to keep the timer tick on for RCU.
550 config 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.
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.
570 Say Y only if you're working on the development of an
571 architecture backend for the context tracking.
573 Say N otherwise, this option brings an overhead that you
574 don't want in production.
577 config 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.
594 Select a specific number if testing RCU itself.
595 Take the default if unsure.
597 config 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.
618 Select a specific number if testing RCU itself.
620 Select the maximum permissible value for large systems.
622 Take the default if unsure.
624 config 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().
637 Say Y if energy efficiency is critically important, and you
638 don't care about increased grace-period durations.
640 Say N if you are unsure.
642 config 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.
650 config 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.
660 Say Y here if you are working with real-time apps or heavy loads
661 Say N here if you are unsure.
663 config 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.
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.
692 Specify the real-time priority, or take the default if unsure.
694 config 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.
705 Accept the default if unsure.
707 config RCU_NOCB_CPU
708 bool "Offload RCU callback processing from boot-selected CPUs"
709 depends on TREE_RCU || PREEMPT_RCU
710 default n
711 help
712 Use this option to reduce OS jitter for aggressive HPC or
713 real-time workloads. It can also be used to offload RCU
714 callback invocation to energy-efficient CPUs in battery-powered
715 asymmetric multiprocessors.
717 This option offloads callback invocation from the set of
718 CPUs specified at boot time by the rcu_nocbs parameter.
719 For each such CPU, a kthread ("rcuox/N") will be created to
720 invoke callbacks, where the "N" is the CPU being offloaded,
721 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
722 "s" for RCU-sched. Nothing prevents this kthread from running
723 on the specified CPUs, but (1) the kthreads may be preempted
724 between each callback, and (2) affinity or cgroups can be used
725 to force the kthreads to run on whatever set of CPUs is desired.
727 Say Y here if you want to help to debug reduced OS jitter.
728 Say N here if you are unsure.
730 choice
731 prompt "Build-forced no-CBs CPUs"
732 default RCU_NOCB_CPU_NONE
733 depends on RCU_NOCB_CPU
734 help
735 This option allows no-CBs CPUs (whose RCU callbacks are invoked
736 from kthreads rather than from softirq context) to be specified
737 at build time. Additional no-CBs CPUs may be specified by
738 the rcu_nocbs= boot parameter.
740 config RCU_NOCB_CPU_NONE
741 bool "No build_forced no-CBs CPUs"
742 help
743 This option does not force any of the CPUs to be no-CBs CPUs.
744 Only CPUs designated by the rcu_nocbs= boot parameter will be
745 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
746 kthreads whose names begin with "rcuo". All other CPUs will
747 invoke their own RCU callbacks in softirq context.
749 Select this option if you want to choose no-CBs CPUs at
750 boot time, for example, to allow testing of different no-CBs
751 configurations without having to rebuild the kernel each time.
753 config RCU_NOCB_CPU_ZERO
754 bool "CPU 0 is a build_forced no-CBs CPU"
755 help
756 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
757 callbacks are invoked by a per-CPU kthread whose name begins
758 with "rcuo". Additional CPUs may be designated as no-CBs
759 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
760 All other CPUs will invoke their own RCU callbacks in softirq
761 context.
763 Select this if CPU 0 needs to be a no-CBs CPU for real-time
764 or energy-efficiency reasons, but the real reason it exists
765 is to ensure that randconfig testing covers mixed systems.
767 config RCU_NOCB_CPU_ALL
768 bool "All CPUs are build_forced no-CBs CPUs"
769 help
770 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
771 boot parameter will be ignored. All CPUs' RCU callbacks will
772 be executed in the context of per-CPU rcuo kthreads created for
773 this purpose. Assuming that the kthreads whose names start with
774 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
775 on the remaining CPUs, but might decrease memory locality during
776 RCU-callback invocation, thus potentially degrading throughput.
778 Select this if all CPUs need to be no-CBs CPUs for real-time
779 or energy-efficiency reasons.
781 endchoice
783 config RCU_EXPEDITE_BOOT
784 bool
785 default n
786 help
787 This option enables expedited grace periods at boot time,
788 as if rcu_expedite_gp() had been invoked early in boot.
789 The corresponding rcu_unexpedite_gp() is invoked from
790 rcu_end_inkernel_boot(), which is intended to be invoked
791 at the end of the kernel-only boot sequence, just before
792 init is exec'ed.
794 Accept the default if unsure.
796 endmenu # "RCU Subsystem"
798 config BUILD_BIN2C
799 bool
800 default n
802 config IKCONFIG
803 tristate "Kernel .config support"
804 select BUILD_BIN2C
805 ---help---
806 This option enables the complete Linux kernel ".config" file
807 contents to be saved in the kernel. It provides documentation
808 of which kernel options are used in a running kernel or in an
809 on-disk kernel. This information can be extracted from the kernel
810 image file with the script scripts/extract-ikconfig and used as
811 input to rebuild the current kernel or to build another kernel.
812 It can also be extracted from a running kernel by reading
813 /proc/config.gz if enabled (below).
815 config IKCONFIG_PROC
816 bool "Enable access to .config through /proc/config.gz"
817 depends on IKCONFIG && PROC_FS
818 ---help---
819 This option enables access to the kernel configuration file
820 through /proc/config.gz.
822 config LOG_BUF_SHIFT
823 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
824 range 12 25
825 default 17
826 depends on PRINTK
827 help
828 Select the minimal kernel log buffer size as a power of 2.
829 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
830 parameter, see below. Any higher size also might be forced
831 by "log_buf_len" boot parameter.
833 Examples:
834 17 => 128 KB
835 16 => 64 KB
836 15 => 32 KB
837 14 => 16 KB
838 13 => 8 KB
839 12 => 4 KB
841 config LOG_CPU_MAX_BUF_SHIFT
842 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
843 depends on SMP
844 range 0 21
845 default 12 if !BASE_SMALL
846 default 0 if BASE_SMALL
847 depends on PRINTK
848 help
849 This option allows to increase the default ring buffer size
850 according to the number of CPUs. The value defines the contribution
851 of each CPU as a power of 2. The used space is typically only few
852 lines however it might be much more when problems are reported,
853 e.g. backtraces.
855 The increased size means that a new buffer has to be allocated and
856 the original static one is unused. It makes sense only on systems
857 with more CPUs. Therefore this value is used only when the sum of
858 contributions is greater than the half of the default kernel ring
859 buffer as defined by LOG_BUF_SHIFT. The default values are set
860 so that more than 64 CPUs are needed to trigger the allocation.
862 Also this option is ignored when "log_buf_len" kernel parameter is
863 used as it forces an exact (power of two) size of the ring buffer.
865 The number of possible CPUs is used for this computation ignoring
866 hotplugging making the compuation optimal for the the worst case
867 scenerio while allowing a simple algorithm to be used from bootup.
869 Examples shift values and their meaning:
870 17 => 128 KB for each CPU
871 16 => 64 KB for each CPU
872 15 => 32 KB for each CPU
873 14 => 16 KB for each CPU
874 13 => 8 KB for each CPU
875 12 => 4 KB for each CPU
877 #
878 # Architectures with an unreliable sched_clock() should select this:
879 #
880 config HAVE_UNSTABLE_SCHED_CLOCK
881 bool
883 config GENERIC_SCHED_CLOCK
884 bool
886 #
887 # For architectures that want to enable the support for NUMA-affine scheduler
888 # balancing logic:
889 #
890 config ARCH_SUPPORTS_NUMA_BALANCING
891 bool
893 #
894 # For architectures that know their GCC __int128 support is sound
895 #
896 config ARCH_SUPPORTS_INT128
897 bool
899 # For architectures that (ab)use NUMA to represent different memory regions
900 # all cpu-local but of different latencies, such as SuperH.
901 #
902 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
903 bool
905 config NUMA_BALANCING
906 bool "Memory placement aware NUMA scheduler"
907 depends on ARCH_SUPPORTS_NUMA_BALANCING
908 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
909 depends on SMP && NUMA && MIGRATION
910 help
911 This option adds support for automatic NUMA aware memory/task placement.
912 The mechanism is quite primitive and is based on migrating memory when
913 it has references to the node the task is running on.
915 This system will be inactive on UMA systems.
917 config NUMA_BALANCING_DEFAULT_ENABLED
918 bool "Automatically enable NUMA aware memory/task placement"
919 default y
920 depends on NUMA_BALANCING
921 help
922 If set, automatic NUMA balancing will be enabled if running on a NUMA
923 machine.
925 menuconfig CGROUPS
926 bool "Control Group support"
927 select KERNFS
928 select PERCPU_RWSEM
929 help
930 This option adds support for grouping sets of processes together, for
931 use with process control subsystems such as Cpusets, CFS, memory
932 controls or device isolation.
933 See
934 - Documentation/scheduler/sched-design-CFS.txt (CFS)
935 - Documentation/cgroups/ (features for grouping, isolation
936 and resource control)
938 Say N if unsure.
940 if CGROUPS
942 config CGROUP_DEBUG
943 bool "Example debug cgroup subsystem"
944 default n
945 help
946 This option enables a simple cgroup subsystem that
947 exports useful debugging information about the cgroups
948 framework.
950 Say N if unsure.
952 config CGROUP_FREEZER
953 bool "Freezer cgroup subsystem"
954 help
955 Provides a way to freeze and unfreeze all tasks in a
956 cgroup.
958 config CGROUP_DEVICE
959 bool "Device controller for cgroups"
960 help
961 Provides a cgroup implementing whitelists for devices which
962 a process in the cgroup can mknod or open.
964 config CPUSETS
965 bool "Cpuset support"
966 help
967 This option will let you create and manage CPUSETs which
968 allow dynamically partitioning a system into sets of CPUs and
969 Memory Nodes and assigning tasks to run only within those sets.
970 This is primarily useful on large SMP or NUMA systems.
972 Say N if unsure.
974 config PROC_PID_CPUSET
975 bool "Include legacy /proc/<pid>/cpuset file"
976 depends on CPUSETS
977 default y
979 config CGROUP_CPUACCT
980 bool "Simple CPU accounting cgroup subsystem"
981 help
982 Provides a simple Resource Controller for monitoring the
983 total CPU consumed by the tasks in a cgroup.
985 config PAGE_COUNTER
986 bool
988 config MEMCG
989 bool "Memory Resource Controller for Control Groups"
990 select PAGE_COUNTER
991 select EVENTFD
992 help
993 Provides a memory resource controller that manages both anonymous
994 memory and page cache. (See Documentation/cgroups/memory.txt)
996 config MEMCG_SWAP
997 bool "Memory Resource Controller Swap Extension"
998 depends on MEMCG && SWAP
999 help
1000 Add swap management feature to memory resource controller. When you
1001 enable this, you can limit mem+swap usage per cgroup. In other words,
1002 when you disable this, memory resource controller has no cares to
1003 usage of swap...a process can exhaust all of the swap. This extension
1004 is useful when you want to avoid exhaustion swap but this itself
1005 adds more overheads and consumes memory for remembering information.
1006 Especially if you use 32bit system or small memory system, please
1007 be careful about enabling this. When memory resource controller
1008 is disabled by boot option, this will be automatically disabled and
1009 there will be no overhead from this. Even when you set this config=y,
1010 if boot option "swapaccount=0" is set, swap will not be accounted.
1011 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1012 size is 4096bytes, 512k per 1Gbytes of swap.
1013 config MEMCG_SWAP_ENABLED
1014 bool "Memory Resource Controller Swap Extension enabled by default"
1015 depends on MEMCG_SWAP
1016 default y
1017 help
1018 Memory Resource Controller Swap Extension comes with its price in
1019 a bigger memory consumption. General purpose distribution kernels
1020 which want to enable the feature but keep it disabled by default
1021 and let the user enable it by swapaccount=1 boot command line
1022 parameter should have this option unselected.
1023 For those who want to have the feature enabled by default should
1024 select this option (if, for some reason, they need to disable it
1025 then swapaccount=0 does the trick).
1026 config MEMCG_KMEM
1027 bool "Memory Resource Controller Kernel Memory accounting"
1028 depends on MEMCG
1029 depends on SLUB || SLAB
1030 help
1031 The Kernel Memory extension for Memory Resource Controller can limit
1032 the amount of memory used by kernel objects in the system. Those are
1033 fundamentally different from the entities handled by the standard
1034 Memory Controller, which are page-based, and can be swapped. Users of
1035 the kmem extension can use it to guarantee that no group of processes
1036 will ever exhaust kernel resources alone.
1038 config CGROUP_HUGETLB
1039 bool "HugeTLB Resource Controller for Control Groups"
1040 depends on HUGETLB_PAGE
1041 select PAGE_COUNTER
1042 default n
1043 help
1044 Provides a cgroup Resource Controller for HugeTLB pages.
1045 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1046 The limit is enforced during page fault. Since HugeTLB doesn't
1047 support page reclaim, enforcing the limit at page fault time implies
1048 that, the application will get SIGBUS signal if it tries to access
1049 HugeTLB pages beyond its limit. This requires the application to know
1050 beforehand how much HugeTLB pages it would require for its use. The
1051 control group is tracked in the third page lru pointer. This means
1052 that we cannot use the controller with huge page less than 3 pages.
1054 config CGROUP_PERF
1055 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1056 depends on PERF_EVENTS && CGROUPS
1057 help
1058 This option extends the per-cpu mode to restrict monitoring to
1059 threads which belong to the cgroup specified and run on the
1060 designated cpu.
1062 Say N if unsure.
1064 menuconfig CGROUP_SCHED
1065 bool "Group CPU scheduler"
1066 default n
1067 help
1068 This feature lets CPU scheduler recognize task groups and control CPU
1069 bandwidth allocation to such task groups. It uses cgroups to group
1070 tasks.
1072 if CGROUP_SCHED
1073 config FAIR_GROUP_SCHED
1074 bool "Group scheduling for SCHED_OTHER"
1075 depends on CGROUP_SCHED
1076 default CGROUP_SCHED
1078 config CFS_BANDWIDTH
1079 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1080 depends on FAIR_GROUP_SCHED
1081 default n
1082 help
1083 This option allows users to define CPU bandwidth rates (limits) for
1084 tasks running within the fair group scheduler. Groups with no limit
1085 set are considered to be unconstrained and will run with no
1086 restriction.
1087 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1089 config RT_GROUP_SCHED
1090 bool "Group scheduling for SCHED_RR/FIFO"
1091 depends on CGROUP_SCHED
1092 default n
1093 help
1094 This feature lets you explicitly allocate real CPU bandwidth
1095 to task groups. If enabled, it will also make it impossible to
1096 schedule realtime tasks for non-root users until you allocate
1097 realtime bandwidth for them.
1098 See Documentation/scheduler/sched-rt-group.txt for more information.
1100 endif #CGROUP_SCHED
1102 config BLK_CGROUP
1103 bool "Block IO controller"
1104 depends on BLOCK
1105 default n
1106 ---help---
1107 Generic block IO controller cgroup interface. This is the common
1108 cgroup interface which should be used by various IO controlling
1109 policies.
1111 Currently, CFQ IO scheduler uses it to recognize task groups and
1112 control disk bandwidth allocation (proportional time slice allocation)
1113 to such task groups. It is also used by bio throttling logic in
1114 block layer to implement upper limit in IO rates on a device.
1116 This option only enables generic Block IO controller infrastructure.
1117 One needs to also enable actual IO controlling logic/policy. For
1118 enabling proportional weight division of disk bandwidth in CFQ, set
1119 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1120 CONFIG_BLK_DEV_THROTTLING=y.
1122 See Documentation/cgroups/blkio-controller.txt for more information.
1124 config DEBUG_BLK_CGROUP
1125 bool "Enable Block IO controller debugging"
1126 depends on BLK_CGROUP
1127 default n
1128 ---help---
1129 Enable some debugging help. Currently it exports additional stat
1130 files in a cgroup which can be useful for debugging.
1132 config CGROUP_WRITEBACK
1133 bool
1134 depends on MEMCG && BLK_CGROUP
1135 default y
1137 endif # CGROUPS
1139 config CHECKPOINT_RESTORE
1140 bool "Checkpoint/restore support" if EXPERT
1141 select PROC_CHILDREN
1142 default n
1143 help
1144 Enables additional kernel features in a sake of checkpoint/restore.
1145 In particular it adds auxiliary prctl codes to setup process text,
1146 data and heap segment sizes, and a few additional /proc filesystem
1147 entries.
1149 If unsure, say N here.
1151 menuconfig NAMESPACES
1152 bool "Namespaces support" if EXPERT
1153 depends on MULTIUSER
1154 default !EXPERT
1155 help
1156 Provides the way to make tasks work with different objects using
1157 the same id. For example same IPC id may refer to different objects
1158 or same user id or pid may refer to different tasks when used in
1159 different namespaces.
1161 if NAMESPACES
1163 config UTS_NS
1164 bool "UTS namespace"
1165 default y
1166 help
1167 In this namespace tasks see different info provided with the
1168 uname() system call
1170 config IPC_NS
1171 bool "IPC namespace"
1172 depends on (SYSVIPC || POSIX_MQUEUE)
1173 default y
1174 help
1175 In this namespace tasks work with IPC ids which correspond to
1176 different IPC objects in different namespaces.
1178 config USER_NS
1179 bool "User namespace"
1180 default n
1181 help
1182 This allows containers, i.e. vservers, to use user namespaces
1183 to provide different user info for different servers.
1185 When user namespaces are enabled in the kernel it is
1186 recommended that the MEMCG and MEMCG_KMEM options also be
1187 enabled and that user-space use the memory control groups to
1188 limit the amount of memory a memory unprivileged users can
1189 use.
1191 If unsure, say N.
1193 config PID_NS
1194 bool "PID Namespaces"
1195 default y
1196 help
1197 Support process id namespaces. This allows having multiple
1198 processes with the same pid as long as they are in different
1199 pid namespaces. This is a building block of containers.
1201 config NET_NS
1202 bool "Network namespace"
1203 depends on NET
1204 default y
1205 help
1206 Allow user space to create what appear to be multiple instances
1207 of the network stack.
1209 endif # NAMESPACES
1211 config SCHED_AUTOGROUP
1212 bool "Automatic process group scheduling"
1213 select CGROUPS
1214 select CGROUP_SCHED
1215 select FAIR_GROUP_SCHED
1216 help
1217 This option optimizes the scheduler for common desktop workloads by
1218 automatically creating and populating task groups. This separation
1219 of workloads isolates aggressive CPU burners (like build jobs) from
1220 desktop applications. Task group autogeneration is currently based
1221 upon task session.
1223 config SYSFS_DEPRECATED
1224 bool "Enable deprecated sysfs features to support old userspace tools"
1225 depends on SYSFS
1226 default n
1227 help
1228 This option adds code that switches the layout of the "block" class
1229 devices, to not show up in /sys/class/block/, but only in
1230 /sys/block/.
1232 This switch is only active when the sysfs.deprecated=1 boot option is
1233 passed or the SYSFS_DEPRECATED_V2 option is set.
1235 This option allows new kernels to run on old distributions and tools,
1236 which might get confused by /sys/class/block/. Since 2007/2008 all
1237 major distributions and tools handle this just fine.
1239 Recent distributions and userspace tools after 2009/2010 depend on
1240 the existence of /sys/class/block/, and will not work with this
1241 option enabled.
1243 Only if you are using a new kernel on an old distribution, you might
1244 need to say Y here.
1246 config SYSFS_DEPRECATED_V2
1247 bool "Enable deprecated sysfs features by default"
1248 default n
1249 depends on SYSFS
1250 depends on SYSFS_DEPRECATED
1251 help
1252 Enable deprecated sysfs by default.
1254 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1255 option.
1257 Only if you are using a new kernel on an old distribution, you might
1258 need to say Y here. Even then, odds are you would not need it
1259 enabled, you can always pass the boot option if absolutely necessary.
1261 config RELAY
1262 bool "Kernel->user space relay support (formerly relayfs)"
1263 help
1264 This option enables support for relay interface support in
1265 certain file systems (such as debugfs).
1266 It is designed to provide an efficient mechanism for tools and
1267 facilities to relay large amounts of data from kernel space to
1268 user space.
1270 If unsure, say N.
1272 config BLK_DEV_INITRD
1273 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1274 depends on BROKEN || !FRV
1275 help
1276 The initial RAM filesystem is a ramfs which is loaded by the
1277 boot loader (loadlin or lilo) and that is mounted as root
1278 before the normal boot procedure. It is typically used to
1279 load modules needed to mount the "real" root file system,
1280 etc. See <file:Documentation/initrd.txt> for details.
1282 If RAM disk support (BLK_DEV_RAM) is also included, this
1283 also enables initial RAM disk (initrd) support and adds
1284 15 Kbytes (more on some other architectures) to the kernel size.
1286 If unsure say Y.
1288 if BLK_DEV_INITRD
1290 source "usr/Kconfig"
1292 endif
1294 config CC_OPTIMIZE_FOR_SIZE
1295 bool "Optimize for size"
1296 help
1297 Enabling this option will pass "-Os" instead of "-O2" to
1298 your compiler resulting in a smaller kernel.
1300 If unsure, say N.
1302 config SYSCTL
1303 bool
1305 config ANON_INODES
1306 bool
1308 config HAVE_UID16
1309 bool
1311 config SYSCTL_EXCEPTION_TRACE
1312 bool
1313 help
1314 Enable support for /proc/sys/debug/exception-trace.
1316 config SYSCTL_ARCH_UNALIGN_NO_WARN
1317 bool
1318 help
1319 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1320 Allows arch to define/use @no_unaligned_warning to possibly warn
1321 about unaligned access emulation going on under the hood.
1323 config SYSCTL_ARCH_UNALIGN_ALLOW
1324 bool
1325 help
1326 Enable support for /proc/sys/kernel/unaligned-trap
1327 Allows arches to define/use @unaligned_enabled to runtime toggle
1328 the unaligned access emulation.
1329 see arch/parisc/kernel/unaligned.c for reference
1331 config HAVE_PCSPKR_PLATFORM
1332 bool
1334 # interpreter that classic socket filters depend on
1335 config BPF
1336 bool
1338 menuconfig EXPERT
1339 bool "Configure standard kernel features (expert users)"
1340 # Unhide debug options, to make the on-by-default options visible
1341 select DEBUG_KERNEL
1342 help
1343 This option allows certain base kernel options and settings
1344 to be disabled or tweaked. This is for specialized
1345 environments which can tolerate a "non-standard" kernel.
1346 Only use this if you really know what you are doing.
1348 config UID16
1349 bool "Enable 16-bit UID system calls" if EXPERT
1350 depends on HAVE_UID16 && MULTIUSER
1351 default y
1352 help
1353 This enables the legacy 16-bit UID syscall wrappers.
1355 config MULTIUSER
1356 bool "Multiple users, groups and capabilities support" if EXPERT
1357 default y
1358 help
1359 This option enables support for non-root users, groups and
1360 capabilities.
1362 If you say N here, all processes will run with UID 0, GID 0, and all
1363 possible capabilities. Saying N here also compiles out support for
1364 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1365 setgid, and capset.
1367 If unsure, say Y here.
1369 config SGETMASK_SYSCALL
1370 bool "sgetmask/ssetmask syscalls support" if EXPERT
1371 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1372 ---help---
1373 sys_sgetmask and sys_ssetmask are obsolete system calls
1374 no longer supported in libc but still enabled by default in some
1375 architectures.
1377 If unsure, leave the default option here.
1379 config SYSFS_SYSCALL
1380 bool "Sysfs syscall support" if EXPERT
1381 default y
1382 ---help---
1383 sys_sysfs is an obsolete system call no longer supported in libc.
1384 Note that disabling this option is more secure but might break
1385 compatibility with some systems.
1387 If unsure say Y here.
1389 config SYSCTL_SYSCALL
1390 bool "Sysctl syscall support" if EXPERT
1391 depends on PROC_SYSCTL
1392 default n
1393 select SYSCTL
1394 ---help---
1395 sys_sysctl uses binary paths that have been found challenging
1396 to properly maintain and use. The interface in /proc/sys
1397 using paths with ascii names is now the primary path to this
1398 information.
1400 Almost nothing using the binary sysctl interface so if you are
1401 trying to save some space it is probably safe to disable this,
1402 making your kernel marginally smaller.
1404 If unsure say N here.
1406 config KALLSYMS
1407 bool "Load all symbols for debugging/ksymoops" if EXPERT
1408 default y
1409 help
1410 Say Y here to let the kernel print out symbolic crash information and
1411 symbolic stack backtraces. This increases the size of the kernel
1412 somewhat, as all symbols have to be loaded into the kernel image.
1414 config KALLSYMS_ALL
1415 bool "Include all symbols in kallsyms"
1416 depends on DEBUG_KERNEL && KALLSYMS
1417 help
1418 Normally kallsyms only contains the symbols of functions for nicer
1419 OOPS messages and backtraces (i.e., symbols from the text and inittext
1420 sections). This is sufficient for most cases. And only in very rare
1421 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1422 names of variables from the data sections, etc).
1424 This option makes sure that all symbols are loaded into the kernel
1425 image (i.e., symbols from all sections) in cost of increased kernel
1426 size (depending on the kernel configuration, it may be 300KiB or
1427 something like this).
1429 Say N unless you really need all symbols.
1431 config PRINTK
1432 default y
1433 bool "Enable support for printk" if EXPERT
1434 select IRQ_WORK
1435 help
1436 This option enables normal printk support. Removing it
1437 eliminates most of the message strings from the kernel image
1438 and makes the kernel more or less silent. As this makes it
1439 very difficult to diagnose system problems, saying N here is
1440 strongly discouraged.
1442 config BUG
1443 bool "BUG() support" if EXPERT
1444 default y
1445 help
1446 Disabling this option eliminates support for BUG and WARN, reducing
1447 the size of your kernel image and potentially quietly ignoring
1448 numerous fatal conditions. You should only consider disabling this
1449 option for embedded systems with no facilities for reporting errors.
1450 Just say Y.
1452 config ELF_CORE
1453 depends on COREDUMP
1454 default y
1455 bool "Enable ELF core dumps" if EXPERT
1456 help
1457 Enable support for generating core dumps. Disabling saves about 4k.
1460 config PCSPKR_PLATFORM
1461 bool "Enable PC-Speaker support" if EXPERT
1462 depends on HAVE_PCSPKR_PLATFORM
1463 select I8253_LOCK
1464 default y
1465 help
1466 This option allows to disable the internal PC-Speaker
1467 support, saving some memory.
1469 config BASE_FULL
1470 default y
1471 bool "Enable full-sized data structures for core" if EXPERT
1472 help
1473 Disabling this option reduces the size of miscellaneous core
1474 kernel data structures. This saves memory on small machines,
1475 but may reduce performance.
1477 config FUTEX
1478 bool "Enable futex support" if EXPERT
1479 default y
1480 select RT_MUTEXES
1481 help
1482 Disabling this option will cause the kernel to be built without
1483 support for "fast userspace mutexes". The resulting kernel may not
1484 run glibc-based applications correctly.
1486 config HAVE_FUTEX_CMPXCHG
1487 bool
1488 depends on FUTEX
1489 help
1490 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1491 is implemented and always working. This removes a couple of runtime
1492 checks.
1494 config EPOLL
1495 bool "Enable eventpoll support" if EXPERT
1496 default y
1497 select ANON_INODES
1498 help
1499 Disabling this option will cause the kernel to be built without
1500 support for epoll family of system calls.
1502 config SIGNALFD
1503 bool "Enable signalfd() system call" if EXPERT
1504 select ANON_INODES
1505 default y
1506 help
1507 Enable the signalfd() system call that allows to receive signals
1508 on a file descriptor.
1510 If unsure, say Y.
1512 config TIMERFD
1513 bool "Enable timerfd() system call" if EXPERT
1514 select ANON_INODES
1515 default y
1516 help
1517 Enable the timerfd() system call that allows to receive timer
1518 events on a file descriptor.
1520 If unsure, say Y.
1522 config EVENTFD
1523 bool "Enable eventfd() system call" if EXPERT
1524 select ANON_INODES
1525 default y
1526 help
1527 Enable the eventfd() system call that allows to receive both
1528 kernel notification (ie. KAIO) or userspace notifications.
1530 If unsure, say Y.
1532 # syscall, maps, verifier
1533 config BPF_SYSCALL
1534 bool "Enable bpf() system call"
1535 select ANON_INODES
1536 select BPF
1537 default n
1538 help
1539 Enable the bpf() system call that allows to manipulate eBPF
1540 programs and maps via file descriptors.
1542 config SHMEM
1543 bool "Use full shmem filesystem" if EXPERT
1544 default y
1545 depends on MMU
1546 help
1547 The shmem is an internal filesystem used to manage shared memory.
1548 It is backed by swap and manages resource limits. It is also exported
1549 to userspace as tmpfs if TMPFS is enabled. Disabling this
1550 option replaces shmem and tmpfs with the much simpler ramfs code,
1551 which may be appropriate on small systems without swap.
1553 config AIO
1554 bool "Enable AIO support" if EXPERT
1555 default y
1556 help
1557 This option enables POSIX asynchronous I/O which may by used
1558 by some high performance threaded applications. Disabling
1559 this option saves about 7k.
1561 config ADVISE_SYSCALLS
1562 bool "Enable madvise/fadvise syscalls" if EXPERT
1563 default y
1564 help
1565 This option enables the madvise and fadvise syscalls, used by
1566 applications to advise the kernel about their future memory or file
1567 usage, improving performance. If building an embedded system where no
1568 applications use these syscalls, you can disable this option to save
1569 space.
1571 config PCI_QUIRKS
1572 default y
1573 bool "Enable PCI quirk workarounds" if EXPERT
1574 depends on PCI
1575 help
1576 This enables workarounds for various PCI chipset
1577 bugs/quirks. Disable this only if your target machine is
1578 unaffected by PCI quirks.
1580 config EMBEDDED
1581 bool "Embedded system"
1582 option allnoconfig_y
1583 select EXPERT
1584 help
1585 This option should be enabled if compiling the kernel for
1586 an embedded system so certain expert options are available
1587 for configuration.
1589 config HAVE_PERF_EVENTS
1590 bool
1591 help
1592 See tools/perf/design.txt for details.
1594 config PERF_USE_VMALLOC
1595 bool
1596 help
1597 See tools/perf/design.txt for details
1599 menu "Kernel Performance Events And Counters"
1601 config PERF_EVENTS
1602 bool "Kernel performance events and counters"
1603 default y if PROFILING
1604 depends on HAVE_PERF_EVENTS
1605 select ANON_INODES
1606 select IRQ_WORK
1607 select SRCU
1608 help
1609 Enable kernel support for various performance events provided
1610 by software and hardware.
1612 Software events are supported either built-in or via the
1613 use of generic tracepoints.
1615 Most modern CPUs support performance events via performance
1616 counter registers. These registers count the number of certain
1617 types of hw events: such as instructions executed, cachemisses
1618 suffered, or branches mis-predicted - without slowing down the
1619 kernel or applications. These registers can also trigger interrupts
1620 when a threshold number of events have passed - and can thus be
1621 used to profile the code that runs on that CPU.
1623 The Linux Performance Event subsystem provides an abstraction of
1624 these software and hardware event capabilities, available via a
1625 system call and used by the "perf" utility in tools/perf/. It
1626 provides per task and per CPU counters, and it provides event
1627 capabilities on top of those.
1629 Say Y if unsure.
1631 config DEBUG_PERF_USE_VMALLOC
1632 default n
1633 bool "Debug: use vmalloc to back perf mmap() buffers"
1634 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1635 select PERF_USE_VMALLOC
1636 help
1637 Use vmalloc memory to back perf mmap() buffers.
1639 Mostly useful for debugging the vmalloc code on platforms
1640 that don't require it.
1642 Say N if unsure.
1644 endmenu
1646 config VM_EVENT_COUNTERS
1647 default y
1648 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1649 help
1650 VM event counters are needed for event counts to be shown.
1651 This option allows the disabling of the VM event counters
1652 on EXPERT systems. /proc/vmstat will only show page counts
1653 if VM event counters are disabled.
1655 config SLUB_DEBUG
1656 default y
1657 bool "Enable SLUB debugging support" if EXPERT
1658 depends on SLUB && SYSFS
1659 help
1660 SLUB has extensive debug support features. Disabling these can
1661 result in significant savings in code size. This also disables
1662 SLUB sysfs support. /sys/slab will not exist and there will be
1663 no support for cache validation etc.
1665 config COMPAT_BRK
1666 bool "Disable heap randomization"
1667 default y
1668 help
1669 Randomizing heap placement makes heap exploits harder, but it
1670 also breaks ancient binaries (including anything libc5 based).
1671 This option changes the bootup default to heap randomization
1672 disabled, and can be overridden at runtime by setting
1673 /proc/sys/kernel/randomize_va_space to 2.
1675 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1677 choice
1678 prompt "Choose SLAB allocator"
1679 default SLUB
1680 help
1681 This option allows to select a slab allocator.
1683 config SLAB
1684 bool "SLAB"
1685 help
1686 The regular slab allocator that is established and known to work
1687 well in all environments. It organizes cache hot objects in
1688 per cpu and per node queues.
1690 config SLUB
1691 bool "SLUB (Unqueued Allocator)"
1692 help
1693 SLUB is a slab allocator that minimizes cache line usage
1694 instead of managing queues of cached objects (SLAB approach).
1695 Per cpu caching is realized using slabs of objects instead
1696 of queues of objects. SLUB can use memory efficiently
1697 and has enhanced diagnostics. SLUB is the default choice for
1698 a slab allocator.
1700 config SLOB
1701 depends on EXPERT
1702 bool "SLOB (Simple Allocator)"
1703 help
1704 SLOB replaces the stock allocator with a drastically simpler
1705 allocator. SLOB is generally more space efficient but
1706 does not perform as well on large systems.
1708 endchoice
1710 config SLUB_CPU_PARTIAL
1711 default y
1712 depends on SLUB && SMP
1713 bool "SLUB per cpu partial cache"
1714 help
1715 Per cpu partial caches accellerate objects allocation and freeing
1716 that is local to a processor at the price of more indeterminism
1717 in the latency of the free. On overflow these caches will be cleared
1718 which requires the taking of locks that may cause latency spikes.
1719 Typically one would choose no for a realtime system.
1721 config MMAP_ALLOW_UNINITIALIZED
1722 bool "Allow mmapped anonymous memory to be uninitialized"
1723 depends on EXPERT && !MMU
1724 default n
1725 help
1726 Normally, and according to the Linux spec, anonymous memory obtained
1727 from mmap() has it's contents cleared before it is passed to
1728 userspace. Enabling this config option allows you to request that
1729 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1730 providing a huge performance boost. If this option is not enabled,
1731 then the flag will be ignored.
1733 This is taken advantage of by uClibc's malloc(), and also by
1734 ELF-FDPIC binfmt's brk and stack allocator.
1736 Because of the obvious security issues, this option should only be
1737 enabled on embedded devices where you control what is run in
1738 userspace. Since that isn't generally a problem on no-MMU systems,
1739 it is normally safe to say Y here.
1741 See Documentation/nommu-mmap.txt for more information.
1743 config SYSTEM_TRUSTED_KEYRING
1744 bool "Provide system-wide ring of trusted keys"
1745 depends on KEYS
1746 help
1747 Provide a system keyring to which trusted keys can be added. Keys in
1748 the keyring are considered to be trusted. Keys may be added at will
1749 by the kernel from compiled-in data and from hardware key stores, but
1750 userspace may only add extra keys if those keys can be verified by
1751 keys already in the keyring.
1753 Keys in this keyring are used by module signature checking.
1755 config PROFILING
1756 bool "Profiling support"
1757 help
1758 Say Y here to enable the extended profiling support mechanisms used
1759 by profilers such as OProfile.
1761 #
1762 # Place an empty function call at each tracepoint site. Can be
1763 # dynamically changed for a probe function.
1764 #
1765 config TRACEPOINTS
1766 bool
1768 source "arch/Kconfig"
1770 endmenu # General setup
1772 config HAVE_GENERIC_DMA_COHERENT
1773 bool
1774 default n
1776 config SLABINFO
1777 bool
1778 depends on PROC_FS
1779 depends on SLAB || SLUB_DEBUG
1780 default y
1782 config RT_MUTEXES
1783 bool
1785 config BASE_SMALL
1786 int
1787 default 0 if BASE_FULL
1788 default 1 if !BASE_FULL
1790 menuconfig MODULES
1791 bool "Enable loadable module support"
1792 option modules
1793 help
1794 Kernel modules are small pieces of compiled code which can
1795 be inserted in the running kernel, rather than being
1796 permanently built into the kernel. You use the "modprobe"
1797 tool to add (and sometimes remove) them. If you say Y here,
1798 many parts of the kernel can be built as modules (by
1799 answering M instead of Y where indicated): this is most
1800 useful for infrequently used options which are not required
1801 for booting. For more information, see the man pages for
1802 modprobe, lsmod, modinfo, insmod and rmmod.
1804 If you say Y here, you will need to run "make
1805 modules_install" to put the modules under /lib/modules/
1806 where modprobe can find them (you may need to be root to do
1807 this).
1809 If unsure, say Y.
1811 if MODULES
1813 config MODULE_FORCE_LOAD
1814 bool "Forced module loading"
1815 default n
1816 help
1817 Allow loading of modules without version information (ie. modprobe
1818 --force). Forced module loading sets the 'F' (forced) taint flag and
1819 is usually a really bad idea.
1821 config MODULE_UNLOAD
1822 bool "Module unloading"
1823 help
1824 Without this option you will not be able to unload any
1825 modules (note that some modules may not be unloadable
1826 anyway), which makes your kernel smaller, faster
1827 and simpler. If unsure, say Y.
1829 config MODULE_FORCE_UNLOAD
1830 bool "Forced module unloading"
1831 depends on MODULE_UNLOAD
1832 help
1833 This option allows you to force a module to unload, even if the
1834 kernel believes it is unsafe: the kernel will remove the module
1835 without waiting for anyone to stop using it (using the -f option to
1836 rmmod). This is mainly for kernel developers and desperate users.
1837 If unsure, say N.
1839 config MODVERSIONS
1840 bool "Module versioning support"
1841 help
1842 Usually, you have to use modules compiled with your kernel.
1843 Saying Y here makes it sometimes possible to use modules
1844 compiled for different kernels, by adding enough information
1845 to the modules to (hopefully) spot any changes which would
1846 make them incompatible with the kernel you are running. If
1847 unsure, say N.
1849 config MODULE_SRCVERSION_ALL
1850 bool "Source checksum for all modules"
1851 help
1852 Modules which contain a MODULE_VERSION get an extra "srcversion"
1853 field inserted into their modinfo section, which contains a
1854 sum of the source files which made it. This helps maintainers
1855 see exactly which source was used to build a module (since
1856 others sometimes change the module source without updating
1857 the version). With this option, such a "srcversion" field
1858 will be created for all modules. If unsure, say N.
1860 config MODULE_SIG
1861 bool "Module signature verification"
1862 depends on MODULES
1863 select SYSTEM_TRUSTED_KEYRING
1864 select KEYS
1865 select CRYPTO
1866 select ASYMMETRIC_KEY_TYPE
1867 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1868 select PUBLIC_KEY_ALGO_RSA
1869 select ASN1
1870 select OID_REGISTRY
1871 select X509_CERTIFICATE_PARSER
1872 help
1873 Check modules for valid signatures upon load: the signature
1874 is simply appended to the module. For more information see
1875 Documentation/module-signing.txt.
1877 !!!WARNING!!! If you enable this option, you MUST make sure that the
1878 module DOES NOT get stripped after being signed. This includes the
1879 debuginfo strip done by some packagers (such as rpmbuild) and
1880 inclusion into an initramfs that wants the module size reduced.
1882 config MODULE_SIG_FORCE
1883 bool "Require modules to be validly signed"
1884 depends on MODULE_SIG
1885 help
1886 Reject unsigned modules or signed modules for which we don't have a
1887 key. Without this, such modules will simply taint the kernel.
1889 config MODULE_SIG_ALL
1890 bool "Automatically sign all modules"
1891 default y
1892 depends on MODULE_SIG
1893 help
1894 Sign all modules during make modules_install. Without this option,
1895 modules must be signed manually, using the scripts/sign-file tool.
1897 comment "Do not forget to sign required modules with scripts/sign-file"
1898 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1900 choice
1901 prompt "Which hash algorithm should modules be signed with?"
1902 depends on MODULE_SIG
1903 help
1904 This determines which sort of hashing algorithm will be used during
1905 signature generation. This algorithm _must_ be built into the kernel
1906 directly so that signature verification can take place. It is not
1907 possible to load a signed module containing the algorithm to check
1908 the signature on that module.
1910 config MODULE_SIG_SHA1
1911 bool "Sign modules with SHA-1"
1912 select CRYPTO_SHA1
1914 config MODULE_SIG_SHA224
1915 bool "Sign modules with SHA-224"
1916 select CRYPTO_SHA256
1918 config MODULE_SIG_SHA256
1919 bool "Sign modules with SHA-256"
1920 select CRYPTO_SHA256
1922 config MODULE_SIG_SHA384
1923 bool "Sign modules with SHA-384"
1924 select CRYPTO_SHA512
1926 config MODULE_SIG_SHA512
1927 bool "Sign modules with SHA-512"
1928 select CRYPTO_SHA512
1930 endchoice
1932 config MODULE_SIG_HASH
1933 string
1934 depends on MODULE_SIG
1935 default "sha1" if MODULE_SIG_SHA1
1936 default "sha224" if MODULE_SIG_SHA224
1937 default "sha256" if MODULE_SIG_SHA256
1938 default "sha384" if MODULE_SIG_SHA384
1939 default "sha512" if MODULE_SIG_SHA512
1941 config MODULE_COMPRESS
1942 bool "Compress modules on installation"
1943 depends on MODULES
1944 help
1946 Compresses kernel modules when 'make modules_install' is run; gzip or
1947 xz depending on "Compression algorithm" below.
1949 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
1951 Out-of-tree kernel modules installed using Kbuild will also be
1952 compressed upon installation.
1954 Note: for modules inside an initrd or initramfs, it's more efficient
1955 to compress the whole initrd or initramfs instead.
1957 Note: This is fully compatible with signed modules.
1959 If in doubt, say N.
1961 choice
1962 prompt "Compression algorithm"
1963 depends on MODULE_COMPRESS
1964 default MODULE_COMPRESS_GZIP
1965 help
1966 This determines which sort of compression will be used during
1967 'make modules_install'.
1969 GZIP (default) and XZ are supported.
1971 config MODULE_COMPRESS_GZIP
1972 bool "GZIP"
1974 config MODULE_COMPRESS_XZ
1975 bool "XZ"
1977 endchoice
1979 endif # MODULES
1981 config MODULES_TREE_LOOKUP
1982 def_bool y
1983 depends on PERF_EVENTS || TRACING
1985 config INIT_ALL_POSSIBLE
1986 bool
1987 help
1988 Back when each arch used to define their own cpu_online_mask and
1989 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1990 with all 1s, and others with all 0s. When they were centralised,
1991 it was better to provide this option than to break all the archs
1992 and have several arch maintainers pursuing me down dark alleys.
1994 config STOP_MACHINE
1995 bool
1996 default y
1997 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1998 help
1999 Need stop_machine() primitive.
2001 source "block/Kconfig"
2003 config PREEMPT_NOTIFIERS
2004 bool
2006 config PADATA
2007 depends on SMP
2008 bool
2010 # Can be selected by architectures with broken toolchains
2011 # that get confused by correct const<->read_only section
2012 # mappings
2013 config BROKEN_RODATA
2014 bool
2016 config ASN1
2017 tristate
2018 help
2019 Build a simple ASN.1 grammar compiler that produces a bytecode output
2020 that can be interpreted by the ASN.1 stream decoder and used to
2021 inform it as to what tags are to be expected in a stream and what
2022 functions to call on what tags.
2024 source "kernel/Kconfig.locks"