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"
28 depends on HAVE_IRQ_WORK
33 bool "Prompt for development and/or incomplete code/drivers"
35 Some of the various things that Linux supports (such as network
36 drivers, file systems, network protocols, etc.) can be in a state
37 of development where the functionality, stability, or the level of
38 testing is not yet high enough for general use. This is usually
39 known as the "alpha-test" phase among developers. If a feature is
40 currently in alpha-test, then the developers usually discourage
41 uninformed widespread use of this feature by the general public to
42 avoid "Why doesn't this work?" type mail messages. However, active
43 testing and use of these systems is welcomed. Just be aware that it
44 may not meet the normal level of reliability or it may fail to work
45 in some special cases. Detailed bug reports from people familiar
46 with the kernel internals are usually welcomed by the developers
47 (before submitting bug reports, please read the documents
48 <file:README>, <file:MAINTAINERS>, <file:REPORTING-BUGS>,
49 <file:Documentation/BUG-HUNTING>, and
50 <file:Documentation/oops-tracing.txt> in the kernel source).
52 This option will also make obsoleted drivers available. These are
53 drivers that have been replaced by something else, and/or are
54 scheduled to be removed in a future kernel release.
56 Unless you intend to help test and develop a feature or driver that
57 falls into this category, or you have a situation that requires
58 using these features, you should probably say N here, which will
59 cause the configurator to present you with fewer choices. If
60 you say Y here, you will be offered the choice of using features or
61 drivers that are currently considered to be in the alpha-test phase.
68 depends on BROKEN || !SMP
71 config INIT_ENV_ARG_LIMIT
76 Maximum of each of the number of arguments and environment
77 variables passed to init from the kernel command line.
81 string "Cross-compiler tool prefix"
83 Same as running 'make CROSS_COMPILE=prefix-' but stored for
84 default make runs in this kernel build directory. You don't
85 need to set this unless you want the configured kernel build
86 directory to select the cross-compiler automatically.
89 string "Local version - append to kernel release"
91 Append an extra string to the end of your kernel version.
92 This will show up when you type uname, for example.
93 The string you set here will be appended after the contents of
94 any files with a filename matching localversion* in your
95 object and source tree, in that order. Your total string can
96 be a maximum of 64 characters.
98 config LOCALVERSION_AUTO
99 bool "Automatically append version information to the version string"
102 This will try to automatically determine if the current tree is a
103 release tree by looking for git tags that belong to the current
104 top of tree revision.
106 A string of the format -gxxxxxxxx will be added to the localversion
107 if a git-based tree is found. The string generated by this will be
108 appended after any matching localversion* files, and after the value
109 set in CONFIG_LOCALVERSION.
111 (The actual string used here is the first eight characters produced
112 by running the command:
114 $ git rev-parse --verify HEAD
116 which is done within the script "scripts/setlocalversion".)
118 config HAVE_KERNEL_GZIP
121 config HAVE_KERNEL_BZIP2
124 config HAVE_KERNEL_LZMA
127 config HAVE_KERNEL_XZ
130 config HAVE_KERNEL_LZO
134 prompt "Kernel compression mode"
136 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO
138 The linux kernel is a kind of self-extracting executable.
139 Several compression algorithms are available, which differ
140 in efficiency, compression and decompression speed.
141 Compression speed is only relevant when building a kernel.
142 Decompression speed is relevant at each boot.
144 If you have any problems with bzip2 or lzma compressed
145 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
146 version of this functionality (bzip2 only), for 2.4, was
147 supplied by Christian Ludwig)
149 High compression options are mostly useful for users, who
150 are low on disk space (embedded systems), but for whom ram
153 If in doubt, select 'gzip'
157 depends on HAVE_KERNEL_GZIP
159 The old and tried gzip compression. It provides a good balance
160 between compression ratio and decompression speed.
164 depends on HAVE_KERNEL_BZIP2
166 Its compression ratio and speed is intermediate.
167 Decompression speed is slowest among the three. The kernel
168 size is about 10% smaller with bzip2, in comparison to gzip.
169 Bzip2 uses a large amount of memory. For modern kernels you
170 will need at least 8MB RAM or more for booting.
174 depends on HAVE_KERNEL_LZMA
176 The most recent compression algorithm.
177 Its ratio is best, decompression speed is between the other
178 two. Compression is slowest. The kernel size is about 33%
179 smaller with LZMA in comparison to gzip.
183 depends on HAVE_KERNEL_XZ
185 XZ uses the LZMA2 algorithm and instruction set specific
186 BCJ filters which can improve compression ratio of executable
187 code. The size of the kernel is about 30% smaller with XZ in
188 comparison to gzip. On architectures for which there is a BCJ
189 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
190 will create a few percent smaller kernel than plain LZMA.
192 The speed is about the same as with LZMA: The decompression
193 speed of XZ is better than that of bzip2 but worse than gzip
194 and LZO. Compression is slow.
198 depends on HAVE_KERNEL_LZO
200 Its compression ratio is the poorest among the 4. The kernel
201 size is about 10% bigger than gzip; however its speed
202 (both compression and decompression) is the fastest.
206 config DEFAULT_HOSTNAME
207 string "Default hostname"
210 This option determines the default system hostname before userspace
211 calls sethostname(2). The kernel traditionally uses "(none)" here,
212 but you may wish to use a different default here to make a minimal
213 system more usable with less configuration.
216 bool "Support for paging of anonymous memory (swap)"
217 depends on MMU && BLOCK
220 This option allows you to choose whether you want to have support
221 for so called swap devices or swap files in your kernel that are
222 used to provide more virtual memory than the actual RAM present
223 in your computer. If unsure say Y.
228 Inter Process Communication is a suite of library functions and
229 system calls which let processes (running programs) synchronize and
230 exchange information. It is generally considered to be a good thing,
231 and some programs won't run unless you say Y here. In particular, if
232 you want to run the DOS emulator dosemu under Linux (read the
233 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
234 you'll need to say Y here.
236 You can find documentation about IPC with "info ipc" and also in
237 section 6.4 of the Linux Programmer's Guide, available from
238 <http://www.tldp.org/guides.html>.
240 config SYSVIPC_SYSCTL
247 bool "POSIX Message Queues"
248 depends on NET && EXPERIMENTAL
250 POSIX variant of message queues is a part of IPC. In POSIX message
251 queues every message has a priority which decides about succession
252 of receiving it by a process. If you want to compile and run
253 programs written e.g. for Solaris with use of its POSIX message
254 queues (functions mq_*) say Y here.
256 POSIX message queues are visible as a filesystem called 'mqueue'
257 and can be mounted somewhere if you want to do filesystem
258 operations on message queues.
262 config POSIX_MQUEUE_SYSCTL
264 depends on POSIX_MQUEUE
268 config BSD_PROCESS_ACCT
269 bool "BSD Process Accounting"
271 If you say Y here, a user level program will be able to instruct the
272 kernel (via a special system call) to write process accounting
273 information to a file: whenever a process exits, information about
274 that process will be appended to the file by the kernel. The
275 information includes things such as creation time, owning user,
276 command name, memory usage, controlling terminal etc. (the complete
277 list is in the struct acct in <file:include/linux/acct.h>). It is
278 up to the user level program to do useful things with this
279 information. This is generally a good idea, so say Y.
281 config BSD_PROCESS_ACCT_V3
282 bool "BSD Process Accounting version 3 file format"
283 depends on BSD_PROCESS_ACCT
286 If you say Y here, the process accounting information is written
287 in a new file format that also logs the process IDs of each
288 process and it's parent. Note that this file format is incompatible
289 with previous v0/v1/v2 file formats, so you will need updated tools
290 for processing it. A preliminary version of these tools is available
291 at <http://www.gnu.org/software/acct/>.
294 bool "open by fhandle syscalls"
297 If you say Y here, a user level program will be able to map
298 file names to handle and then later use the handle for
299 different file system operations. This is useful in implementing
300 userspace file servers, which now track files using handles instead
301 of names. The handle would remain the same even if file names
302 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
306 bool "Export task/process statistics through netlink (EXPERIMENTAL)"
310 Export selected statistics for tasks/processes through the
311 generic netlink interface. Unlike BSD process accounting, the
312 statistics are available during the lifetime of tasks/processes as
313 responses to commands. Like BSD accounting, they are sent to user
318 config TASK_DELAY_ACCT
319 bool "Enable per-task delay accounting (EXPERIMENTAL)"
322 Collect information on time spent by a task waiting for system
323 resources like cpu, synchronous block I/O completion and swapping
324 in pages. Such statistics can help in setting a task's priorities
325 relative to other tasks for cpu, io, rss limits etc.
330 bool "Enable extended accounting over taskstats (EXPERIMENTAL)"
333 Collect extended task accounting data and send the data
334 to userland for processing over the taskstats interface.
338 config TASK_IO_ACCOUNTING
339 bool "Enable per-task storage I/O accounting (EXPERIMENTAL)"
340 depends on TASK_XACCT
342 Collect information on the number of bytes of storage I/O which this
348 bool "Auditing support"
351 Enable auditing infrastructure that can be used with another
352 kernel subsystem, such as SELinux (which requires this for
353 logging of avc messages output). Does not do system-call
354 auditing without CONFIG_AUDITSYSCALL.
357 bool "Enable system-call auditing support"
358 depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH)
359 default y if SECURITY_SELINUX
361 Enable low-overhead system-call auditing infrastructure that
362 can be used independently or with another kernel subsystem,
367 depends on AUDITSYSCALL
372 depends on AUDITSYSCALL
375 source "kernel/irq/Kconfig"
380 prompt "RCU Implementation"
384 bool "Tree-based hierarchical RCU"
385 depends on !PREEMPT && SMP
387 This option selects the RCU implementation that is
388 designed for very large SMP system with hundreds or
389 thousands of CPUs. It also scales down nicely to
392 config TREE_PREEMPT_RCU
393 bool "Preemptible tree-based hierarchical RCU"
396 This option selects the RCU implementation that is
397 designed for very large SMP systems with hundreds or
398 thousands of CPUs, but for which real-time response
399 is also required. It also scales down nicely to
403 bool "UP-only small-memory-footprint RCU"
406 This option selects the RCU implementation that is
407 designed for UP systems from which real-time response
408 is not required. This option greatly reduces the
409 memory footprint of RCU.
411 config TINY_PREEMPT_RCU
412 bool "Preemptible UP-only small-memory-footprint RCU"
413 depends on !SMP && PREEMPT
415 This option selects the RCU implementation that is designed
416 for real-time UP systems. This option greatly reduces the
417 memory footprint of RCU.
422 def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
424 This option enables preemptible-RCU code that is common between
425 the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
428 bool "Enable tracing for RCU"
430 This option provides tracing in RCU which presents stats
431 in debugfs for debugging RCU implementation.
433 Say Y here if you want to enable RCU tracing
434 Say N if you are unsure.
437 int "Tree-based hierarchical RCU fanout value"
440 depends on TREE_RCU || TREE_PREEMPT_RCU
444 This option controls the fanout of hierarchical implementations
445 of RCU, allowing RCU to work efficiently on machines with
446 large numbers of CPUs. This value must be at least the fourth
447 root of NR_CPUS, which allows NR_CPUS to be insanely large.
448 The default value of RCU_FANOUT should be used for production
449 systems, but if you are stress-testing the RCU implementation
450 itself, small RCU_FANOUT values allow you to test large-system
451 code paths on small(er) systems.
453 Select a specific number if testing RCU itself.
454 Take the default if unsure.
456 config RCU_FANOUT_EXACT
457 bool "Disable tree-based hierarchical RCU auto-balancing"
458 depends on TREE_RCU || TREE_PREEMPT_RCU
461 This option forces use of the exact RCU_FANOUT value specified,
462 regardless of imbalances in the hierarchy. This is useful for
463 testing RCU itself, and might one day be useful on systems with
464 strong NUMA behavior.
466 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
470 config RCU_FAST_NO_HZ
471 bool "Accelerate last non-dyntick-idle CPU's grace periods"
472 depends on TREE_RCU && NO_HZ && SMP
475 This option causes RCU to attempt to accelerate grace periods
476 in order to allow the final CPU to enter dynticks-idle state
477 more quickly. On the other hand, this option increases the
478 overhead of the dynticks-idle checking, particularly on systems
479 with large numbers of CPUs.
481 Say Y if energy efficiency is critically important, particularly
482 if you have relatively few CPUs.
484 Say N if you are unsure.
486 config TREE_RCU_TRACE
487 def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
490 This option provides tracing for the TREE_RCU and
491 TREE_PREEMPT_RCU implementations, permitting Makefile to
492 trivially select kernel/rcutree_trace.c.
495 bool "Enable RCU priority boosting"
496 depends on RT_MUTEXES && PREEMPT_RCU
499 This option boosts the priority of preempted RCU readers that
500 block the current preemptible RCU grace period for too long.
501 This option also prevents heavy loads from blocking RCU
502 callback invocation for all flavors of RCU.
504 Say Y here if you are working with real-time apps or heavy loads
505 Say N here if you are unsure.
507 config RCU_BOOST_PRIO
508 int "Real-time priority to boost RCU readers to"
513 This option specifies the real-time priority to which preempted
514 RCU readers are to be boosted. If you are working with CPU-bound
515 real-time applications, you should specify a priority higher then
516 the highest-priority CPU-bound application.
518 Specify the real-time priority, or take the default if unsure.
520 config RCU_BOOST_DELAY
521 int "Milliseconds to delay boosting after RCU grace-period start"
526 This option specifies the time to wait after the beginning of
527 a given grace period before priority-boosting preempted RCU
528 readers blocking that grace period. Note that any RCU reader
529 blocking an expedited RCU grace period is boosted immediately.
531 Accept the default if unsure.
533 endmenu # "RCU Subsystem"
536 tristate "Kernel .config support"
538 This option enables the complete Linux kernel ".config" file
539 contents to be saved in the kernel. It provides documentation
540 of which kernel options are used in a running kernel or in an
541 on-disk kernel. This information can be extracted from the kernel
542 image file with the script scripts/extract-ikconfig and used as
543 input to rebuild the current kernel or to build another kernel.
544 It can also be extracted from a running kernel by reading
545 /proc/config.gz if enabled (below).
548 bool "Enable access to .config through /proc/config.gz"
549 depends on IKCONFIG && PROC_FS
551 This option enables access to the kernel configuration file
552 through /proc/config.gz.
555 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
559 Select kernel log buffer size as a power of 2.
569 # Architectures with an unreliable sched_clock() should select this:
571 config HAVE_UNSTABLE_SCHED_CLOCK
575 boolean "Control Group support"
578 This option adds support for grouping sets of processes together, for
579 use with process control subsystems such as Cpusets, CFS, memory
580 controls or device isolation.
582 - Documentation/scheduler/sched-design-CFS.txt (CFS)
583 - Documentation/cgroups/ (features for grouping, isolation
584 and resource control)
591 bool "Example debug cgroup subsystem"
594 This option enables a simple cgroup subsystem that
595 exports useful debugging information about the cgroups
600 config CGROUP_FREEZER
601 bool "Freezer cgroup subsystem"
603 Provides a way to freeze and unfreeze all tasks in a
607 bool "Device controller for cgroups"
609 Provides a cgroup implementing whitelists for devices which
610 a process in the cgroup can mknod or open.
613 bool "Cpuset support"
615 This option will let you create and manage CPUSETs which
616 allow dynamically partitioning a system into sets of CPUs and
617 Memory Nodes and assigning tasks to run only within those sets.
618 This is primarily useful on large SMP or NUMA systems.
622 config PROC_PID_CPUSET
623 bool "Include legacy /proc/<pid>/cpuset file"
627 config CGROUP_CPUACCT
628 bool "Simple CPU accounting cgroup subsystem"
630 Provides a simple Resource Controller for monitoring the
631 total CPU consumed by the tasks in a cgroup.
633 config RESOURCE_COUNTERS
634 bool "Resource counters"
636 This option enables controller independent resource accounting
637 infrastructure that works with cgroups.
639 config CGROUP_MEM_RES_CTLR
640 bool "Memory Resource Controller for Control Groups"
641 depends on RESOURCE_COUNTERS
644 Provides a memory resource controller that manages both anonymous
645 memory and page cache. (See Documentation/cgroups/memory.txt)
647 Note that setting this option increases fixed memory overhead
648 associated with each page of memory in the system. By this,
649 20(40)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
650 usage tracking struct at boot. Total amount of this is printed out
653 Only enable when you're ok with these trade offs and really
654 sure you need the memory resource controller. Even when you enable
655 this, you can set "cgroup_disable=memory" at your boot option to
656 disable memory resource controller and you can avoid overheads.
657 (and lose benefits of memory resource controller)
659 This config option also selects MM_OWNER config option, which
660 could in turn add some fork/exit overhead.
662 config CGROUP_MEM_RES_CTLR_SWAP
663 bool "Memory Resource Controller Swap Extension"
664 depends on CGROUP_MEM_RES_CTLR && SWAP
666 Add swap management feature to memory resource controller. When you
667 enable this, you can limit mem+swap usage per cgroup. In other words,
668 when you disable this, memory resource controller has no cares to
669 usage of swap...a process can exhaust all of the swap. This extension
670 is useful when you want to avoid exhaustion swap but this itself
671 adds more overheads and consumes memory for remembering information.
672 Especially if you use 32bit system or small memory system, please
673 be careful about enabling this. When memory resource controller
674 is disabled by boot option, this will be automatically disabled and
675 there will be no overhead from this. Even when you set this config=y,
676 if boot option "swapaccount=0" is set, swap will not be accounted.
677 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
678 size is 4096bytes, 512k per 1Gbytes of swap.
679 config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
680 bool "Memory Resource Controller Swap Extension enabled by default"
681 depends on CGROUP_MEM_RES_CTLR_SWAP
684 Memory Resource Controller Swap Extension comes with its price in
685 a bigger memory consumption. General purpose distribution kernels
686 which want to enable the feature but keep it disabled by default
687 and let the user enable it by swapaccount boot command line
688 parameter should have this option unselected.
689 For those who want to have the feature enabled by default should
690 select this option (if, for some reason, they need to disable it
691 then swapaccount=0 does the trick).
694 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
695 depends on PERF_EVENTS && CGROUPS
697 This option extends the per-cpu mode to restrict monitoring to
698 threads which belong to the cgroup specified and run on the
703 menuconfig CGROUP_SCHED
704 bool "Group CPU scheduler"
705 depends on EXPERIMENTAL
708 This feature lets CPU scheduler recognize task groups and control CPU
709 bandwidth allocation to such task groups. It uses cgroups to group
713 config FAIR_GROUP_SCHED
714 bool "Group scheduling for SCHED_OTHER"
715 depends on CGROUP_SCHED
718 config RT_GROUP_SCHED
719 bool "Group scheduling for SCHED_RR/FIFO"
720 depends on EXPERIMENTAL
721 depends on CGROUP_SCHED
724 This feature lets you explicitly allocate real CPU bandwidth
725 to task groups. If enabled, it will also make it impossible to
726 schedule realtime tasks for non-root users until you allocate
727 realtime bandwidth for them.
728 See Documentation/scheduler/sched-rt-group.txt for more information.
733 tristate "Block IO controller"
737 Generic block IO controller cgroup interface. This is the common
738 cgroup interface which should be used by various IO controlling
741 Currently, CFQ IO scheduler uses it to recognize task groups and
742 control disk bandwidth allocation (proportional time slice allocation)
743 to such task groups. It is also used by bio throttling logic in
744 block layer to implement upper limit in IO rates on a device.
746 This option only enables generic Block IO controller infrastructure.
747 One needs to also enable actual IO controlling logic/policy. For
748 enabling proportional weight division of disk bandwidth in CFQ, set
749 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
750 CONFIG_BLK_DEV_THROTTLING=y.
752 See Documentation/cgroups/blkio-controller.txt for more information.
754 config DEBUG_BLK_CGROUP
755 bool "Enable Block IO controller debugging"
756 depends on BLK_CGROUP
759 Enable some debugging help. Currently it exports additional stat
760 files in a cgroup which can be useful for debugging.
764 menuconfig NAMESPACES
765 bool "Namespaces support" if EXPERT
768 Provides the way to make tasks work with different objects using
769 the same id. For example same IPC id may refer to different objects
770 or same user id or pid may refer to different tasks when used in
771 different namespaces.
779 In this namespace tasks see different info provided with the
784 depends on (SYSVIPC || POSIX_MQUEUE)
787 In this namespace tasks work with IPC ids which correspond to
788 different IPC objects in different namespaces.
791 bool "User namespace (EXPERIMENTAL)"
792 depends on EXPERIMENTAL
795 This allows containers, i.e. vservers, to use user namespaces
796 to provide different user info for different servers.
800 bool "PID Namespaces"
803 Support process id namespaces. This allows having multiple
804 processes with the same pid as long as they are in different
805 pid namespaces. This is a building block of containers.
808 bool "Network namespace"
812 Allow user space to create what appear to be multiple instances
813 of the network stack.
817 config SCHED_AUTOGROUP
818 bool "Automatic process group scheduling"
822 select FAIR_GROUP_SCHED
824 This option optimizes the scheduler for common desktop workloads by
825 automatically creating and populating task groups. This separation
826 of workloads isolates aggressive CPU burners (like build jobs) from
827 desktop applications. Task group autogeneration is currently based
833 config SYSFS_DEPRECATED
834 bool "Enable deprecated sysfs features to support old userspace tools"
838 This option adds code that switches the layout of the "block" class
839 devices, to not show up in /sys/class/block/, but only in
842 This switch is only active when the sysfs.deprecated=1 boot option is
843 passed or the SYSFS_DEPRECATED_V2 option is set.
845 This option allows new kernels to run on old distributions and tools,
846 which might get confused by /sys/class/block/. Since 2007/2008 all
847 major distributions and tools handle this just fine.
849 Recent distributions and userspace tools after 2009/2010 depend on
850 the existence of /sys/class/block/, and will not work with this
853 Only if you are using a new kernel on an old distribution, you might
856 config SYSFS_DEPRECATED_V2
857 bool "Enable deprecated sysfs features by default"
860 depends on SYSFS_DEPRECATED
862 Enable deprecated sysfs by default.
864 See the CONFIG_SYSFS_DEPRECATED option for more details about this
867 Only if you are using a new kernel on an old distribution, you might
868 need to say Y here. Even then, odds are you would not need it
869 enabled, you can always pass the boot option if absolutely necessary.
872 bool "Kernel->user space relay support (formerly relayfs)"
874 This option enables support for relay interface support in
875 certain file systems (such as debugfs).
876 It is designed to provide an efficient mechanism for tools and
877 facilities to relay large amounts of data from kernel space to
882 config BLK_DEV_INITRD
883 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
884 depends on BROKEN || !FRV
886 The initial RAM filesystem is a ramfs which is loaded by the
887 boot loader (loadlin or lilo) and that is mounted as root
888 before the normal boot procedure. It is typically used to
889 load modules needed to mount the "real" root file system,
890 etc. See <file:Documentation/initrd.txt> for details.
892 If RAM disk support (BLK_DEV_RAM) is also included, this
893 also enables initial RAM disk (initrd) support and adds
894 15 Kbytes (more on some other architectures) to the kernel size.
904 config CC_OPTIMIZE_FOR_SIZE
905 bool "Optimize for size"
907 Enabling this option will pass "-Os" instead of "-O2" to gcc
908 resulting in a smaller kernel.
919 bool "Configure standard kernel features (expert users)"
920 # Unhide debug options, to make the on-by-default options visible
923 This option allows certain base kernel options and settings
924 to be disabled or tweaked. This is for specialized
925 environments which can tolerate a "non-standard" kernel.
926 Only use this if you really know what you are doing.
929 bool "Enable 16-bit UID system calls" if EXPERT
930 depends on ARM || BLACKFIN || CRIS || FRV || H8300 || X86_32 || M68K || (S390 && !64BIT) || SUPERH || SPARC32 || (SPARC64 && COMPAT) || UML || (X86_64 && IA32_EMULATION)
933 This enables the legacy 16-bit UID syscall wrappers.
935 config SYSCTL_SYSCALL
936 bool "Sysctl syscall support" if EXPERT
937 depends on PROC_SYSCTL
941 sys_sysctl uses binary paths that have been found challenging
942 to properly maintain and use. The interface in /proc/sys
943 using paths with ascii names is now the primary path to this
946 Almost nothing using the binary sysctl interface so if you are
947 trying to save some space it is probably safe to disable this,
948 making your kernel marginally smaller.
950 If unsure say Y here.
953 bool "Load all symbols for debugging/ksymoops" if EXPERT
956 Say Y here to let the kernel print out symbolic crash information and
957 symbolic stack backtraces. This increases the size of the kernel
958 somewhat, as all symbols have to be loaded into the kernel image.
961 bool "Include all symbols in kallsyms"
962 depends on DEBUG_KERNEL && KALLSYMS
964 Normally kallsyms only contains the symbols of functions for nicer
965 OOPS messages and backtraces (i.e., symbols from the text and inittext
966 sections). This is sufficient for most cases. And only in very rare
967 cases (e.g., when a debugger is used) all symbols are required (e.g.,
968 names of variables from the data sections, etc).
970 This option makes sure that all symbols are loaded into the kernel
971 image (i.e., symbols from all sections) in cost of increased kernel
972 size (depending on the kernel configuration, it may be 300KiB or
973 something like this).
975 Say N unless you really need all symbols.
978 bool "Support for hot-pluggable devices" if EXPERT
981 This option is provided for the case where no hotplug or uevent
982 capabilities is wanted by the kernel. You should only consider
983 disabling this option for embedded systems that do not use modules, a
984 dynamic /dev tree, or dynamic device discovery. Just say Y.
988 bool "Enable support for printk" if EXPERT
990 This option enables normal printk support. Removing it
991 eliminates most of the message strings from the kernel image
992 and makes the kernel more or less silent. As this makes it
993 very difficult to diagnose system problems, saying N here is
994 strongly discouraged.
997 bool "BUG() support" if EXPERT
1000 Disabling this option eliminates support for BUG and WARN, reducing
1001 the size of your kernel image and potentially quietly ignoring
1002 numerous fatal conditions. You should only consider disabling this
1003 option for embedded systems with no facilities for reporting errors.
1008 bool "Enable ELF core dumps" if EXPERT
1010 Enable support for generating core dumps. Disabling saves about 4k.
1013 config PCSPKR_PLATFORM
1014 bool "Enable PC-Speaker support" if EXPERT
1015 depends on HAVE_PCSPKR_PLATFORM
1019 This option allows to disable the internal PC-Speaker
1020 support, saving some memory.
1022 config HAVE_PCSPKR_PLATFORM
1027 bool "Enable full-sized data structures for core" if EXPERT
1029 Disabling this option reduces the size of miscellaneous core
1030 kernel data structures. This saves memory on small machines,
1031 but may reduce performance.
1034 bool "Enable futex support" if EXPERT
1038 Disabling this option will cause the kernel to be built without
1039 support for "fast userspace mutexes". The resulting kernel may not
1040 run glibc-based applications correctly.
1043 bool "Enable eventpoll support" if EXPERT
1047 Disabling this option will cause the kernel to be built without
1048 support for epoll family of system calls.
1051 bool "Enable signalfd() system call" if EXPERT
1055 Enable the signalfd() system call that allows to receive signals
1056 on a file descriptor.
1061 bool "Enable timerfd() system call" if EXPERT
1065 Enable the timerfd() system call that allows to receive timer
1066 events on a file descriptor.
1071 bool "Enable eventfd() system call" if EXPERT
1075 Enable the eventfd() system call that allows to receive both
1076 kernel notification (ie. KAIO) or userspace notifications.
1081 bool "Use full shmem filesystem" if EXPERT
1085 The shmem is an internal filesystem used to manage shared memory.
1086 It is backed by swap and manages resource limits. It is also exported
1087 to userspace as tmpfs if TMPFS is enabled. Disabling this
1088 option replaces shmem and tmpfs with the much simpler ramfs code,
1089 which may be appropriate on small systems without swap.
1092 bool "Enable AIO support" if EXPERT
1095 This option enables POSIX asynchronous I/O which may by used
1096 by some high performance threaded applications. Disabling
1097 this option saves about 7k.
1100 bool "Embedded system"
1103 This option should be enabled if compiling the kernel for
1104 an embedded system so certain expert options are available
1107 config HAVE_PERF_EVENTS
1110 See tools/perf/design.txt for details.
1112 config PERF_USE_VMALLOC
1115 See tools/perf/design.txt for details
1117 menu "Kernel Performance Events And Counters"
1120 bool "Kernel performance events and counters"
1121 default y if (PROFILING || PERF_COUNTERS)
1122 depends on HAVE_PERF_EVENTS
1126 Enable kernel support for various performance events provided
1127 by software and hardware.
1129 Software events are supported either built-in or via the
1130 use of generic tracepoints.
1132 Most modern CPUs support performance events via performance
1133 counter registers. These registers count the number of certain
1134 types of hw events: such as instructions executed, cachemisses
1135 suffered, or branches mis-predicted - without slowing down the
1136 kernel or applications. These registers can also trigger interrupts
1137 when a threshold number of events have passed - and can thus be
1138 used to profile the code that runs on that CPU.
1140 The Linux Performance Event subsystem provides an abstraction of
1141 these software and hardware event capabilities, available via a
1142 system call and used by the "perf" utility in tools/perf/. It
1143 provides per task and per CPU counters, and it provides event
1144 capabilities on top of those.
1148 config PERF_COUNTERS
1149 bool "Kernel performance counters (old config option)"
1150 depends on HAVE_PERF_EVENTS
1152 This config has been obsoleted by the PERF_EVENTS
1153 config option - please see that one for details.
1155 It has no effect on the kernel whether you enable
1156 it or not, it is a compatibility placeholder.
1160 config DEBUG_PERF_USE_VMALLOC
1162 bool "Debug: use vmalloc to back perf mmap() buffers"
1163 depends on PERF_EVENTS && DEBUG_KERNEL
1164 select PERF_USE_VMALLOC
1166 Use vmalloc memory to back perf mmap() buffers.
1168 Mostly useful for debugging the vmalloc code on platforms
1169 that don't require it.
1175 config VM_EVENT_COUNTERS
1177 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1179 VM event counters are needed for event counts to be shown.
1180 This option allows the disabling of the VM event counters
1181 on EXPERT systems. /proc/vmstat will only show page counts
1182 if VM event counters are disabled.
1186 bool "Enable PCI quirk workarounds" if EXPERT
1189 This enables workarounds for various PCI chipset
1190 bugs/quirks. Disable this only if your target machine is
1191 unaffected by PCI quirks.
1195 bool "Enable SLUB debugging support" if EXPERT
1196 depends on SLUB && SYSFS
1198 SLUB has extensive debug support features. Disabling these can
1199 result in significant savings in code size. This also disables
1200 SLUB sysfs support. /sys/slab will not exist and there will be
1201 no support for cache validation etc.
1204 bool "Disable heap randomization"
1207 Randomizing heap placement makes heap exploits harder, but it
1208 also breaks ancient binaries (including anything libc5 based).
1209 This option changes the bootup default to heap randomization
1210 disabled, and can be overridden at runtime by setting
1211 /proc/sys/kernel/randomize_va_space to 2.
1213 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1216 prompt "Choose SLAB allocator"
1219 This option allows to select a slab allocator.
1224 The regular slab allocator that is established and known to work
1225 well in all environments. It organizes cache hot objects in
1226 per cpu and per node queues.
1229 bool "SLUB (Unqueued Allocator)"
1231 SLUB is a slab allocator that minimizes cache line usage
1232 instead of managing queues of cached objects (SLAB approach).
1233 Per cpu caching is realized using slabs of objects instead
1234 of queues of objects. SLUB can use memory efficiently
1235 and has enhanced diagnostics. SLUB is the default choice for
1240 bool "SLOB (Simple Allocator)"
1242 SLOB replaces the stock allocator with a drastically simpler
1243 allocator. SLOB is generally more space efficient but
1244 does not perform as well on large systems.
1248 config MMAP_ALLOW_UNINITIALIZED
1249 bool "Allow mmapped anonymous memory to be uninitialized"
1250 depends on EXPERT && !MMU
1253 Normally, and according to the Linux spec, anonymous memory obtained
1254 from mmap() has it's contents cleared before it is passed to
1255 userspace. Enabling this config option allows you to request that
1256 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1257 providing a huge performance boost. If this option is not enabled,
1258 then the flag will be ignored.
1260 This is taken advantage of by uClibc's malloc(), and also by
1261 ELF-FDPIC binfmt's brk and stack allocator.
1263 Because of the obvious security issues, this option should only be
1264 enabled on embedded devices where you control what is run in
1265 userspace. Since that isn't generally a problem on no-MMU systems,
1266 it is normally safe to say Y here.
1268 See Documentation/nommu-mmap.txt for more information.
1271 bool "Profiling support"
1273 Say Y here to enable the extended profiling support mechanisms used
1274 by profilers such as OProfile.
1277 # Place an empty function call at each tracepoint site. Can be
1278 # dynamically changed for a probe function.
1283 source "arch/Kconfig"
1285 endmenu # General setup
1287 config HAVE_GENERIC_DMA_COHERENT
1294 depends on SLAB || SLUB_DEBUG
1302 default 0 if BASE_FULL
1303 default 1 if !BASE_FULL
1306 bool "Enable loadable module support"
1308 Kernel modules are small pieces of compiled code which can
1309 be inserted in the running kernel, rather than being
1310 permanently built into the kernel. You use the "modprobe"
1311 tool to add (and sometimes remove) them. If you say Y here,
1312 many parts of the kernel can be built as modules (by
1313 answering M instead of Y where indicated): this is most
1314 useful for infrequently used options which are not required
1315 for booting. For more information, see the man pages for
1316 modprobe, lsmod, modinfo, insmod and rmmod.
1318 If you say Y here, you will need to run "make
1319 modules_install" to put the modules under /lib/modules/
1320 where modprobe can find them (you may need to be root to do
1327 config MODULE_FORCE_LOAD
1328 bool "Forced module loading"
1331 Allow loading of modules without version information (ie. modprobe
1332 --force). Forced module loading sets the 'F' (forced) taint flag and
1333 is usually a really bad idea.
1335 config MODULE_UNLOAD
1336 bool "Module unloading"
1338 Without this option you will not be able to unload any
1339 modules (note that some modules may not be unloadable
1340 anyway), which makes your kernel smaller, faster
1341 and simpler. If unsure, say Y.
1343 config MODULE_FORCE_UNLOAD
1344 bool "Forced module unloading"
1345 depends on MODULE_UNLOAD && EXPERIMENTAL
1347 This option allows you to force a module to unload, even if the
1348 kernel believes it is unsafe: the kernel will remove the module
1349 without waiting for anyone to stop using it (using the -f option to
1350 rmmod). This is mainly for kernel developers and desperate users.
1354 bool "Module versioning support"
1356 Usually, you have to use modules compiled with your kernel.
1357 Saying Y here makes it sometimes possible to use modules
1358 compiled for different kernels, by adding enough information
1359 to the modules to (hopefully) spot any changes which would
1360 make them incompatible with the kernel you are running. If
1363 config MODULE_SRCVERSION_ALL
1364 bool "Source checksum for all modules"
1366 Modules which contain a MODULE_VERSION get an extra "srcversion"
1367 field inserted into their modinfo section, which contains a
1368 sum of the source files which made it. This helps maintainers
1369 see exactly which source was used to build a module (since
1370 others sometimes change the module source without updating
1371 the version). With this option, such a "srcversion" field
1372 will be created for all modules. If unsure, say N.
1376 config INIT_ALL_POSSIBLE
1379 Back when each arch used to define their own cpu_online_map and
1380 cpu_possible_map, some of them chose to initialize cpu_possible_map
1381 with all 1s, and others with all 0s. When they were centralised,
1382 it was better to provide this option than to break all the archs
1383 and have several arch maintainers pursuing me down dark alleys.
1388 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1390 Need stop_machine() primitive.
1392 source "block/Kconfig"
1394 config PREEMPT_NOTIFIERS
1401 source "kernel/Kconfig.locks"