7 option env="KERNELVERSION"
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"
22 bool "Prompt for development and/or incomplete code/drivers"
24 Some of the various things that Linux supports (such as network
25 drivers, file systems, network protocols, etc.) can be in a state
26 of development where the functionality, stability, or the level of
27 testing is not yet high enough for general use. This is usually
28 known as the "alpha-test" phase among developers. If a feature is
29 currently in alpha-test, then the developers usually discourage
30 uninformed widespread use of this feature by the general public to
31 avoid "Why doesn't this work?" type mail messages. However, active
32 testing and use of these systems is welcomed. Just be aware that it
33 may not meet the normal level of reliability or it may fail to work
34 in some special cases. Detailed bug reports from people familiar
35 with the kernel internals are usually welcomed by the developers
36 (before submitting bug reports, please read the documents
37 <file:README>, <file:MAINTAINERS>, <file:REPORTING-BUGS>,
38 <file:Documentation/BUG-HUNTING>, and
39 <file:Documentation/oops-tracing.txt> in the kernel source).
41 This option will also make obsoleted drivers available. These are
42 drivers that have been replaced by something else, and/or are
43 scheduled to be removed in a future kernel release.
45 Unless you intend to help test and develop a feature or driver that
46 falls into this category, or you have a situation that requires
47 using these features, you should probably say N here, which will
48 cause the configurator to present you with fewer choices. If
49 you say Y here, you will be offered the choice of using features or
50 drivers that are currently considered to be in the alpha-test phase.
57 depends on BROKEN || !SMP
62 depends on SMP || PREEMPT
65 config INIT_ENV_ARG_LIMIT
70 Maximum of each of the number of arguments and environment
71 variables passed to init from the kernel command line.
75 string "Local version - append to kernel release"
77 Append an extra string to the end of your kernel version.
78 This will show up when you type uname, for example.
79 The string you set here will be appended after the contents of
80 any files with a filename matching localversion* in your
81 object and source tree, in that order. Your total string can
82 be a maximum of 64 characters.
84 config LOCALVERSION_AUTO
85 bool "Automatically append version information to the version string"
88 This will try to automatically determine if the current tree is a
89 release tree by looking for git tags that belong to the current
92 A string of the format -gxxxxxxxx will be added to the localversion
93 if a git-based tree is found. The string generated by this will be
94 appended after any matching localversion* files, and after the value
95 set in CONFIG_LOCALVERSION.
97 (The actual string used here is the first eight characters produced
98 by running the command:
100 $ git rev-parse --verify HEAD
102 which is done within the script "scripts/setlocalversion".)
105 bool "Support for paging of anonymous memory (swap)"
106 depends on MMU && BLOCK
109 This option allows you to choose whether you want to have support
110 for so called swap devices or swap files in your kernel that are
111 used to provide more virtual memory than the actual RAM present
112 in your computer. If unsure say Y.
117 Inter Process Communication is a suite of library functions and
118 system calls which let processes (running programs) synchronize and
119 exchange information. It is generally considered to be a good thing,
120 and some programs won't run unless you say Y here. In particular, if
121 you want to run the DOS emulator dosemu under Linux (read the
122 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
123 you'll need to say Y here.
125 You can find documentation about IPC with "info ipc" and also in
126 section 6.4 of the Linux Programmer's Guide, available from
127 <http://www.tldp.org/guides.html>.
129 config SYSVIPC_SYSCTL
136 bool "POSIX Message Queues"
137 depends on NET && EXPERIMENTAL
139 POSIX variant of message queues is a part of IPC. In POSIX message
140 queues every message has a priority which decides about succession
141 of receiving it by a process. If you want to compile and run
142 programs written e.g. for Solaris with use of its POSIX message
143 queues (functions mq_*) say Y here.
145 POSIX message queues are visible as a filesystem called 'mqueue'
146 and can be mounted somewhere if you want to do filesystem
147 operations on message queues.
151 config BSD_PROCESS_ACCT
152 bool "BSD Process Accounting"
154 If you say Y here, a user level program will be able to instruct the
155 kernel (via a special system call) to write process accounting
156 information to a file: whenever a process exits, information about
157 that process will be appended to the file by the kernel. The
158 information includes things such as creation time, owning user,
159 command name, memory usage, controlling terminal etc. (the complete
160 list is in the struct acct in <file:include/linux/acct.h>). It is
161 up to the user level program to do useful things with this
162 information. This is generally a good idea, so say Y.
164 config BSD_PROCESS_ACCT_V3
165 bool "BSD Process Accounting version 3 file format"
166 depends on BSD_PROCESS_ACCT
169 If you say Y here, the process accounting information is written
170 in a new file format that also logs the process IDs of each
171 process and it's parent. Note that this file format is incompatible
172 with previous v0/v1/v2 file formats, so you will need updated tools
173 for processing it. A preliminary version of these tools is available
174 at <http://www.gnu.org/software/acct/>.
177 bool "Export task/process statistics through netlink (EXPERIMENTAL)"
181 Export selected statistics for tasks/processes through the
182 generic netlink interface. Unlike BSD process accounting, the
183 statistics are available during the lifetime of tasks/processes as
184 responses to commands. Like BSD accounting, they are sent to user
189 config TASK_DELAY_ACCT
190 bool "Enable per-task delay accounting (EXPERIMENTAL)"
193 Collect information on time spent by a task waiting for system
194 resources like cpu, synchronous block I/O completion and swapping
195 in pages. Such statistics can help in setting a task's priorities
196 relative to other tasks for cpu, io, rss limits etc.
201 bool "Enable extended accounting over taskstats (EXPERIMENTAL)"
204 Collect extended task accounting data and send the data
205 to userland for processing over the taskstats interface.
209 config TASK_IO_ACCOUNTING
210 bool "Enable per-task storage I/O accounting (EXPERIMENTAL)"
211 depends on TASK_XACCT
213 Collect information on the number of bytes of storage I/O which this
219 bool "Auditing support"
222 Enable auditing infrastructure that can be used with another
223 kernel subsystem, such as SELinux (which requires this for
224 logging of avc messages output). Does not do system-call
225 auditing without CONFIG_AUDITSYSCALL.
228 bool "Enable system-call auditing support"
229 depends on AUDIT && (X86 || PPC || PPC64 || S390 || IA64 || UML || SPARC64|| SUPERH)
230 default y if SECURITY_SELINUX
232 Enable low-overhead system-call auditing infrastructure that
233 can be used independently or with another kernel subsystem,
234 such as SELinux. To use audit's filesystem watch feature, please
235 ensure that INOTIFY is configured.
239 depends on AUDITSYSCALL && INOTIFY
242 tristate "Kernel .config support"
244 This option enables the complete Linux kernel ".config" file
245 contents to be saved in the kernel. It provides documentation
246 of which kernel options are used in a running kernel or in an
247 on-disk kernel. This information can be extracted from the kernel
248 image file with the script scripts/extract-ikconfig and used as
249 input to rebuild the current kernel or to build another kernel.
250 It can also be extracted from a running kernel by reading
251 /proc/config.gz if enabled (below).
254 bool "Enable access to .config through /proc/config.gz"
255 depends on IKCONFIG && PROC_FS
257 This option enables access to the kernel configuration file
258 through /proc/config.gz.
261 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
265 Select kernel log buffer size as a power of 2.
275 # Architectures with an unreliable sched_clock() should select this:
277 config HAVE_UNSTABLE_SCHED_CLOCK
281 bool "Group CPU scheduler"
282 depends on EXPERIMENTAL
285 This feature lets CPU scheduler recognize task groups and control CPU
286 bandwidth allocation to such task groups.
287 In order to create a group from arbitrary set of processes, use
288 CONFIG_CGROUPS. (See Control Group support.)
290 config FAIR_GROUP_SCHED
291 bool "Group scheduling for SCHED_OTHER"
292 depends on GROUP_SCHED
295 config RT_GROUP_SCHED
296 bool "Group scheduling for SCHED_RR/FIFO"
297 depends on EXPERIMENTAL
298 depends on GROUP_SCHED
301 This feature lets you explicitly allocate real CPU bandwidth
302 to users or control groups (depending on the "Basis for grouping tasks"
303 setting below. If enabled, it will also make it impossible to
304 schedule realtime tasks for non-root users until you allocate
305 realtime bandwidth for them.
306 See Documentation/scheduler/sched-rt-group.txt for more information.
309 depends on GROUP_SCHED
310 prompt "Basis for grouping tasks"
316 This option will choose userid as the basis for grouping
317 tasks, thus providing equal CPU bandwidth to each user.
320 bool "Control groups"
323 This option allows you to create arbitrary task groups
324 using the "cgroup" pseudo filesystem and control
325 the cpu bandwidth allocated to each such task group.
326 Refer to Documentation/cgroups.txt for more information
327 on "cgroup" pseudo filesystem.
331 menu "Control Group support"
333 bool "Control Group support"
335 This option add support for grouping sets of processes together, for
336 use with process control subsystems such as Cpusets, CFS, memory
337 controls or device isolation.
339 - Documentation/cpusets.txt (Cpusets)
340 - Documentation/scheduler/sched-design-CFS.txt (CFS)
341 - Documentation/cgroups/ (features for grouping, isolation)
342 - Documentation/controllers/ (features for resource control)
347 bool "Example debug cgroup subsystem"
351 This option enables a simple cgroup subsystem that
352 exports useful debugging information about the cgroups
358 bool "Namespace cgroup subsystem"
361 Provides a simple namespace cgroup subsystem to
362 provide hierarchical naming of sets of namespaces,
363 for instance virtual servers and checkpoint/restart
366 config CGROUP_FREEZER
367 bool "control group freezer subsystem"
370 Provides a way to freeze and unfreeze all tasks in a
374 bool "Device controller for cgroups"
375 depends on CGROUPS && EXPERIMENTAL
377 Provides a cgroup implementing whitelists for devices which
378 a process in the cgroup can mknod or open.
381 bool "Cpuset support"
382 depends on SMP && CGROUPS
384 This option will let you create and manage CPUSETs which
385 allow dynamically partitioning a system into sets of CPUs and
386 Memory Nodes and assigning tasks to run only within those sets.
387 This is primarily useful on large SMP or NUMA systems.
391 config CGROUP_CPUACCT
392 bool "Simple CPU accounting cgroup subsystem"
395 Provides a simple Resource Controller for monitoring the
396 total CPU consumed by the tasks in a cgroup
398 config RESOURCE_COUNTERS
399 bool "Resource counters"
401 This option enables controller independent resource accounting
402 infrastructure that works with cgroups
405 config CGROUP_MEM_RES_CTLR
406 bool "Memory Resource Controller for Control Groups"
407 depends on CGROUPS && RESOURCE_COUNTERS
410 Provides a memory resource controller that manages both anonymous
411 memory and page cache. (See Documentation/controllers/memory.txt)
413 Note that setting this option increases fixed memory overhead
414 associated with each page of memory in the system. By this,
415 20(40)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
416 usage tracking struct at boot. Total amount of this is printed out
419 Only enable when you're ok with these trade offs and really
420 sure you need the memory resource controller. Even when you enable
421 this, you can set "cgroup_disable=memory" at your boot option to
422 disable memory resource controller and you can avoid overheads.
423 (and lose benefits of memory resource controller)
425 This config option also selects MM_OWNER config option, which
426 could in turn add some fork/exit overhead.
433 config SYSFS_DEPRECATED
436 config SYSFS_DEPRECATED_V2
437 bool "Create deprecated sysfs layout for older userspace tools"
440 select SYSFS_DEPRECATED
442 This option switches the layout of sysfs to the deprecated
445 The current sysfs layout features a unified device tree at
446 /sys/devices/, which is able to express a hierarchy between
447 class devices. If the deprecated option is set to Y, the
448 unified device tree is split into a bus device tree at
449 /sys/devices/ and several individual class device trees at
450 /sys/class/. The class and bus devices will be connected by
451 "<subsystem>:<name>" and the "device" links. The "block"
452 class devices, will not show up in /sys/class/block/. Some
453 subsystems will suppress the creation of some devices which
454 depend on the unified device tree.
456 This option is not a pure compatibility option that can
457 be safely enabled on newer distributions. It will change the
458 layout of sysfs to the non-extensible deprecated version,
459 and disable some features, which can not be exported without
460 confusing older userspace tools. Since 2007/2008 all major
461 distributions do not enable this option, and ship no tools which
462 depend on the deprecated layout or this option.
464 If you are using a new kernel on an older distribution, or use
465 older userspace tools, you might need to say Y here. Do not say Y,
466 if the original kernel, that came with your distribution, has
467 this option set to N.
469 config PROC_PID_CPUSET
470 bool "Include legacy /proc/<pid>/cpuset file"
475 bool "Kernel->user space relay support (formerly relayfs)"
477 This option enables support for relay interface support in
478 certain file systems (such as debugfs).
479 It is designed to provide an efficient mechanism for tools and
480 facilities to relay large amounts of data from kernel space to
486 bool "Namespaces support" if EMBEDDED
489 Provides the way to make tasks work with different objects using
490 the same id. For example same IPC id may refer to different objects
491 or same user id or pid may refer to different tasks when used in
492 different namespaces.
496 depends on NAMESPACES
498 In this namespace tasks see different info provided with the
503 depends on NAMESPACES && SYSVIPC
505 In this namespace tasks work with IPC ids which correspond to
506 different IPC objects in different namespaces
509 bool "User namespace (EXPERIMENTAL)"
510 depends on NAMESPACES && EXPERIMENTAL
512 This allows containers, i.e. vservers, to use user namespaces
513 to provide different user info for different servers.
517 bool "PID Namespaces (EXPERIMENTAL)"
519 depends on NAMESPACES && EXPERIMENTAL
521 Support process id namespaces. This allows having multiple
522 process with the same pid as long as they are in different
523 pid namespaces. This is a building block of containers.
525 Unless you want to work with an experimental feature
528 config BLK_DEV_INITRD
529 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
530 depends on BROKEN || !FRV
532 The initial RAM filesystem is a ramfs which is loaded by the
533 boot loader (loadlin or lilo) and that is mounted as root
534 before the normal boot procedure. It is typically used to
535 load modules needed to mount the "real" root file system,
536 etc. See <file:Documentation/initrd.txt> for details.
538 If RAM disk support (BLK_DEV_RAM) is also included, this
539 also enables initial RAM disk (initrd) support and adds
540 15 Kbytes (more on some other architectures) to the kernel size.
550 config CC_OPTIMIZE_FOR_SIZE
551 bool "Optimize for size"
554 Enabling this option will pass "-Os" instead of "-O2" to gcc
555 resulting in a smaller kernel.
563 bool "Configure standard kernel features (for small systems)"
565 This option allows certain base kernel options and settings
566 to be disabled or tweaked. This is for specialized
567 environments which can tolerate a "non-standard" kernel.
568 Only use this if you really know what you are doing.
571 bool "Enable 16-bit UID system calls" if EMBEDDED
572 depends on ARM || BLACKFIN || CRIS || FRV || H8300 || X86_32 || M68K || (S390 && !64BIT) || SUPERH || SPARC32 || (SPARC64 && COMPAT) || UML || (X86_64 && IA32_EMULATION)
575 This enables the legacy 16-bit UID syscall wrappers.
577 config SYSCTL_SYSCALL
578 bool "Sysctl syscall support" if EMBEDDED
582 sys_sysctl uses binary paths that have been found challenging
583 to properly maintain and use. The interface in /proc/sys
584 using paths with ascii names is now the primary path to this
587 Almost nothing using the binary sysctl interface so if you are
588 trying to save some space it is probably safe to disable this,
589 making your kernel marginally smaller.
591 If unsure say Y here.
594 bool "Load all symbols for debugging/ksymoops" if EMBEDDED
597 Say Y here to let the kernel print out symbolic crash information and
598 symbolic stack backtraces. This increases the size of the kernel
599 somewhat, as all symbols have to be loaded into the kernel image.
602 bool "Include all symbols in kallsyms"
603 depends on DEBUG_KERNEL && KALLSYMS
605 Normally kallsyms only contains the symbols of functions, for nicer
606 OOPS messages. Some debuggers can use kallsyms for other
607 symbols too: say Y here to include all symbols, if you need them
608 and you don't care about adding 300k to the size of your kernel.
612 config KALLSYMS_STRIP_GENERATED
613 bool "Strip machine generated symbols from kallsyms"
614 depends on KALLSYMS_ALL
617 Say N if you want kallsyms to retain even machine generated symbols.
619 config KALLSYMS_EXTRA_PASS
620 bool "Do an extra kallsyms pass"
623 If kallsyms is not working correctly, the build will fail with
624 inconsistent kallsyms data. If that occurs, log a bug report and
625 turn on KALLSYMS_EXTRA_PASS which should result in a stable build.
626 Always say N here unless you find a bug in kallsyms, which must be
627 reported. KALLSYMS_EXTRA_PASS is only a temporary workaround while
628 you wait for kallsyms to be fixed.
632 bool "Support for hot-pluggable devices" if EMBEDDED
635 This option is provided for the case where no hotplug or uevent
636 capabilities is wanted by the kernel. You should only consider
637 disabling this option for embedded systems that do not use modules, a
638 dynamic /dev tree, or dynamic device discovery. Just say Y.
642 bool "Enable support for printk" if EMBEDDED
644 This option enables normal printk support. Removing it
645 eliminates most of the message strings from the kernel image
646 and makes the kernel more or less silent. As this makes it
647 very difficult to diagnose system problems, saying N here is
648 strongly discouraged.
651 bool "BUG() support" if EMBEDDED
654 Disabling this option eliminates support for BUG and WARN, reducing
655 the size of your kernel image and potentially quietly ignoring
656 numerous fatal conditions. You should only consider disabling this
657 option for embedded systems with no facilities for reporting errors.
662 bool "Enable ELF core dumps" if EMBEDDED
664 Enable support for generating core dumps. Disabling saves about 4k.
666 config PCSPKR_PLATFORM
667 bool "Enable PC-Speaker support" if EMBEDDED
668 depends on ALPHA || X86 || MIPS || PPC_PREP || PPC_CHRP || PPC_PSERIES
671 This option allows to disable the internal PC-Speaker
672 support, saving some memory.
675 bool "Disable heap randomization"
678 Randomizing heap placement makes heap exploits harder, but it
679 also breaks ancient binaries (including anything libc5 based).
680 This option changes the bootup default to heap randomization
681 disabled, and can be overriden runtime by setting
682 /proc/sys/kernel/randomize_va_space to 2.
684 On non-ancient distros (post-2000 ones) N is usually a safe choice.
688 bool "Enable full-sized data structures for core" if EMBEDDED
690 Disabling this option reduces the size of miscellaneous core
691 kernel data structures. This saves memory on small machines,
692 but may reduce performance.
695 bool "Enable futex support" if EMBEDDED
699 Disabling this option will cause the kernel to be built without
700 support for "fast userspace mutexes". The resulting kernel may not
701 run glibc-based applications correctly.
707 bool "Enable eventpoll support" if EMBEDDED
711 Disabling this option will cause the kernel to be built without
712 support for epoll family of system calls.
715 bool "Enable signalfd() system call" if EMBEDDED
719 Enable the signalfd() system call that allows to receive signals
720 on a file descriptor.
725 bool "Enable timerfd() system call" if EMBEDDED
729 Enable the timerfd() system call that allows to receive timer
730 events on a file descriptor.
735 bool "Enable eventfd() system call" if EMBEDDED
739 Enable the eventfd() system call that allows to receive both
740 kernel notification (ie. KAIO) or userspace notifications.
745 bool "Use full shmem filesystem" if EMBEDDED
749 The shmem is an internal filesystem used to manage shared memory.
750 It is backed by swap and manages resource limits. It is also exported
751 to userspace as tmpfs if TMPFS is enabled. Disabling this
752 option replaces shmem and tmpfs with the much simpler ramfs code,
753 which may be appropriate on small systems without swap.
756 bool "Enable AIO support" if EMBEDDED
759 This option enables POSIX asynchronous I/O which may by used
760 by some high performance threaded applications. Disabling
761 this option saves about 7k.
763 config VM_EVENT_COUNTERS
765 bool "Enable VM event counters for /proc/vmstat" if EMBEDDED
767 VM event counters are needed for event counts to be shown.
768 This option allows the disabling of the VM event counters
769 on EMBEDDED systems. /proc/vmstat will only show page counts
770 if VM event counters are disabled.
774 bool "Enable PCI quirk workarounds" if EMBEDDED
777 This enables workarounds for various PCI chipset
778 bugs/quirks. Disable this only if your target machine is
779 unaffected by PCI quirks.
783 bool "Enable SLUB debugging support" if EMBEDDED
784 depends on SLUB && SYSFS
786 SLUB has extensive debug support features. Disabling these can
787 result in significant savings in code size. This also disables
788 SLUB sysfs support. /sys/slab will not exist and there will be
789 no support for cache validation etc.
792 prompt "Choose SLAB allocator"
795 This option allows to select a slab allocator.
800 The regular slab allocator that is established and known to work
801 well in all environments. It organizes cache hot objects in
802 per cpu and per node queues.
805 bool "SLUB (Unqueued Allocator)"
807 SLUB is a slab allocator that minimizes cache line usage
808 instead of managing queues of cached objects (SLAB approach).
809 Per cpu caching is realized using slabs of objects instead
810 of queues of objects. SLUB can use memory efficiently
811 and has enhanced diagnostics. SLUB is the default choice for
816 bool "SLOB (Simple Allocator)"
818 SLOB replaces the stock allocator with a drastically simpler
819 allocator. SLOB is generally more space efficient but
820 does not perform as well on large systems.
825 bool "Profiling support (EXPERIMENTAL)"
827 Say Y here to enable the extended profiling support mechanisms used
828 by profilers such as OProfile.
831 # Place an empty function call at each tracepoint site. Can be
832 # dynamically changed for a probe function.
838 bool "Activate markers"
839 depends on TRACEPOINTS
841 Place an empty function call at each marker site. Can be
842 dynamically changed for a probe function.
844 source "arch/Kconfig"
846 endmenu # General setup
848 config HAVE_GENERIC_DMA_COHERENT
855 depends on SLAB || SLUB_DEBUG
864 default 0 if BASE_FULL
865 default 1 if !BASE_FULL
868 bool "Enable loadable module support"
870 Kernel modules are small pieces of compiled code which can
871 be inserted in the running kernel, rather than being
872 permanently built into the kernel. You use the "modprobe"
873 tool to add (and sometimes remove) them. If you say Y here,
874 many parts of the kernel can be built as modules (by
875 answering M instead of Y where indicated): this is most
876 useful for infrequently used options which are not required
877 for booting. For more information, see the man pages for
878 modprobe, lsmod, modinfo, insmod and rmmod.
880 If you say Y here, you will need to run "make
881 modules_install" to put the modules under /lib/modules/
882 where modprobe can find them (you may need to be root to do
889 config MODULE_FORCE_LOAD
890 bool "Forced module loading"
893 Allow loading of modules without version information (ie. modprobe
894 --force). Forced module loading sets the 'F' (forced) taint flag and
895 is usually a really bad idea.
898 bool "Module unloading"
900 Without this option you will not be able to unload any
901 modules (note that some modules may not be unloadable
902 anyway), which makes your kernel smaller, faster
903 and simpler. If unsure, say Y.
905 config MODULE_FORCE_UNLOAD
906 bool "Forced module unloading"
907 depends on MODULE_UNLOAD && EXPERIMENTAL
909 This option allows you to force a module to unload, even if the
910 kernel believes it is unsafe: the kernel will remove the module
911 without waiting for anyone to stop using it (using the -f option to
912 rmmod). This is mainly for kernel developers and desperate users.
916 bool "Module versioning support"
918 Usually, you have to use modules compiled with your kernel.
919 Saying Y here makes it sometimes possible to use modules
920 compiled for different kernels, by adding enough information
921 to the modules to (hopefully) spot any changes which would
922 make them incompatible with the kernel you are running. If
925 config MODULE_SRCVERSION_ALL
926 bool "Source checksum for all modules"
928 Modules which contain a MODULE_VERSION get an extra "srcversion"
929 field inserted into their modinfo section, which contains a
930 sum of the source files which made it. This helps maintainers
931 see exactly which source was used to build a module (since
932 others sometimes change the module source without updating
933 the version). With this option, such a "srcversion" field
934 will be created for all modules. If unsure, say N.
938 config INIT_ALL_POSSIBLE
941 Back when each arch used to define their own cpu_online_map and
942 cpu_possible_map, some of them chose to initialize cpu_possible_map
943 with all 1s, and others with all 0s. When they were centralised,
944 it was better to provide this option than to break all the archs
945 and have several arch maintainers persuing me down dark alleys.
950 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
952 Need stop_machine() primitive.
954 source "block/Kconfig"
956 config PREEMPT_NOTIFIERS
960 prompt "RCU Implementation"
966 This option selects the classic RCU implementation that is
967 designed for best read-side performance on non-realtime
970 Select this option if you are unsure.
973 bool "Tree-based hierarchical RCU"
975 This option selects the RCU implementation that is
976 designed for very large SMP system with hundreds or
980 bool "Preemptible RCU"
983 This option reduces the latency of the kernel by making certain
984 RCU sections preemptible. Normally RCU code is non-preemptible, if
985 this option is selected then read-only RCU sections become
986 preemptible. This helps latency, but may expose bugs due to
987 now-naive assumptions about each RCU read-side critical section
988 remaining on a given CPU through its execution.
993 bool "Enable tracing for RCU"
994 depends on TREE_RCU || PREEMPT_RCU
996 This option provides tracing in RCU which presents stats
997 in debugfs for debugging RCU implementation.
999 Say Y here if you want to enable RCU tracing
1000 Say N if you are unsure.
1003 int "Tree-based hierarchical RCU fanout value"
1005 range 2 32 if !64BIT
1008 default 32 if !64BIT
1010 This option controls the fanout of hierarchical implementations
1011 of RCU, allowing RCU to work efficiently on machines with
1012 large numbers of CPUs. This value must be at least the cube
1013 root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit
1014 systems and up to 262,144 for 64-bit systems.
1016 Select a specific number if testing RCU itself.
1017 Take the default if unsure.
1019 config RCU_FANOUT_EXACT
1020 bool "Disable tree-based hierarchical RCU auto-balancing"
1024 This option forces use of the exact RCU_FANOUT value specified,
1025 regardless of imbalances in the hierarchy. This is useful for
1026 testing RCU itself, and might one day be useful on systems with
1027 strong NUMA behavior.
1029 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
1033 config TREE_RCU_TRACE
1034 def_bool RCU_TRACE && TREE_RCU
1037 This option provides tracing for the TREE_RCU implementation,
1038 permitting Makefile to trivially select kernel/rcutree_trace.c.
1040 config PREEMPT_RCU_TRACE
1041 def_bool RCU_TRACE && PREEMPT_RCU
1044 This option provides tracing for the PREEMPT_RCU implementation,
1045 permitting Makefile to trivially select kernel/rcupreempt_trace.c.
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