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"
26 config BUILDTIME_EXTABLE_SORT
36 depends on BROKEN || !SMP
39 config INIT_ENV_ARG_LIMIT
44 Maximum of each of the number of arguments and environment
45 variables passed to init from the kernel command line.
49 string "Cross-compiler tool prefix"
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.
57 bool "Compile also drivers which will not load"
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.
71 string "Local version - append to kernel release"
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"
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
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
103 config HAVE_KERNEL_BZIP2
106 config HAVE_KERNEL_LZMA
109 config HAVE_KERNEL_XZ
112 config HAVE_KERNEL_LZO
115 config HAVE_KERNEL_LZ4
119 prompt "Kernel compression mode"
121 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
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
138 If in doubt, select 'gzip'
142 depends on HAVE_KERNEL_GZIP
144 The old and tried gzip compression. It provides a good balance
145 between compression ratio and decompression speed.
149 depends on HAVE_KERNEL_BZIP2
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.
159 depends on HAVE_KERNEL_LZMA
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.
167 depends on HAVE_KERNEL_XZ
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.
182 depends on HAVE_KERNEL_LZO
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.
190 depends on HAVE_KERNEL_LZ4
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
202 config DEFAULT_HOSTNAME
203 string "Default hostname"
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.
212 bool "Support for paging of anonymous memory (swap)"
213 depends on MMU && BLOCK
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.
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
243 bool "POSIX Message Queues"
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.
258 config POSIX_MQUEUE_SYSCTL
260 depends on POSIX_MQUEUE
264 config CROSS_MEMORY_ATTACH
265 bool "Enable process_vm_readv/writev syscalls"
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.
275 bool "open by fhandle syscalls"
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)
287 bool "uselib syscall"
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.
297 bool "Auditing support"
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
309 bool "Enable system-call auditing support"
310 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
311 default y if SECURITY_SELINUX
313 Enable low-overhead system-call auditing infrastructure that
314 can be used independently or with another kernel subsystem,
319 depends on AUDITSYSCALL
324 depends on AUDITSYSCALL
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
330 menu "CPU/Task time and stats accounting"
332 config VIRT_CPU_ACCOUNTING
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
345 This is the basic tick based cputime accounting that maintains
346 statistics about user, system and idle time spent on per jiffies
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
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
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
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
377 For now this is only useful if you are working on the full
378 dynticks subsystem development.
382 config IRQ_TIME_ACCOUNTING
383 bool "Fine granularity task level IRQ time accounting"
384 depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
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.
395 config BSD_PROCESS_ACCT
396 bool "BSD Process Accounting"
398 If you say Y here, a user level program will be able to instruct the
399 kernel (via a special system call) to write process accounting
400 information to a file: whenever a process exits, information about
401 that process will be appended to the file by the kernel. The
402 information includes things such as creation time, owning user,
403 command name, memory usage, controlling terminal etc. (the complete
404 list is in the struct acct in <file:include/linux/acct.h>). It is
405 up to the user level program to do useful things with this
406 information. This is generally a good idea, so say Y.
408 config BSD_PROCESS_ACCT_V3
409 bool "BSD Process Accounting version 3 file format"
410 depends on BSD_PROCESS_ACCT
413 If you say Y here, the process accounting information is written
414 in a new file format that also logs the process IDs of each
415 process and it's parent. Note that this file format is incompatible
416 with previous v0/v1/v2 file formats, so you will need updated tools
417 for processing it. A preliminary version of these tools is available
418 at <http://www.gnu.org/software/acct/>.
421 bool "Export task/process statistics through netlink"
425 Export selected statistics for tasks/processes through the
426 generic netlink interface. Unlike BSD process accounting, the
427 statistics are available during the lifetime of tasks/processes as
428 responses to commands. Like BSD accounting, they are sent to user
433 config TASK_DELAY_ACCT
434 bool "Enable per-task delay accounting"
437 Collect information on time spent by a task waiting for system
438 resources like cpu, synchronous block I/O completion and swapping
439 in pages. Such statistics can help in setting a task's priorities
440 relative to other tasks for cpu, io, rss limits etc.
445 bool "Enable extended accounting over taskstats"
448 Collect extended task accounting data and send the data
449 to userland for processing over the taskstats interface.
453 config TASK_IO_ACCOUNTING
454 bool "Enable per-task storage I/O accounting"
455 depends on TASK_XACCT
457 Collect information on the number of bytes of storage I/O which this
462 endmenu # "CPU/Task time and stats accounting"
467 prompt "RCU Implementation"
471 bool "Tree-based hierarchical RCU"
472 depends on !PREEMPT && SMP
475 This option selects the RCU implementation that is
476 designed for very large SMP system with hundreds or
477 thousands of CPUs. It also scales down nicely to
481 bool "Preemptible tree-based hierarchical RCU"
485 This option selects the RCU implementation that is
486 designed for very large SMP systems with hundreds or
487 thousands of CPUs, but for which real-time response
488 is also required. It also scales down nicely to
491 Select this option if you are unsure.
494 bool "UP-only small-memory-footprint RCU"
495 depends on !PREEMPT && !SMP
497 This option selects the RCU implementation that is
498 designed for UP systems from which real-time response
499 is not required. This option greatly reduces the
500 memory footprint of RCU.
505 bool "Task_based RCU implementation using voluntary context switch"
508 This option enables a task-based RCU implementation that uses
509 only voluntary context switch (not preemption!), idle, and
510 user-mode execution as quiescent states.
514 config RCU_STALL_COMMON
515 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
517 This option enables RCU CPU stall code that is common between
518 the TINY and TREE variants of RCU. The purpose is to allow
519 the tiny variants to disable RCU CPU stall warnings, while
520 making these warnings mandatory for the tree variants.
522 config CONTEXT_TRACKING
526 bool "Consider userspace as in RCU extended quiescent state"
527 depends on HAVE_CONTEXT_TRACKING && SMP
528 select CONTEXT_TRACKING
530 This option sets hooks on kernel / userspace boundaries and
531 puts RCU in extended quiescent state when the CPU runs in
532 userspace. It means that when a CPU runs in userspace, it is
533 excluded from the global RCU state machine and thus doesn't
534 try to keep the timer tick on for RCU.
536 Unless you want to hack and help the development of the full
537 dynticks mode, you shouldn't enable this option. It also
538 adds unnecessary overhead.
542 config CONTEXT_TRACKING_FORCE
543 bool "Force context tracking"
544 depends on CONTEXT_TRACKING
545 default y if !NO_HZ_FULL
547 The major pre-requirement for full dynticks to work is to
548 support the context tracking subsystem. But there are also
549 other dependencies to provide in order to make the full
552 This option stands for testing when an arch implements the
553 context tracking backend but doesn't yet fullfill all the
554 requirements to make the full dynticks feature working.
555 Without the full dynticks, there is no way to test the support
556 for context tracking and the subsystems that rely on it: RCU
557 userspace extended quiescent state and tickless cputime
558 accounting. This option copes with the absence of the full
559 dynticks subsystem by forcing the context tracking on all
562 Say Y only if you're working on the development of an
563 architecture backend for the context tracking.
565 Say N otherwise, this option brings an overhead that you
566 don't want in production.
570 int "Tree-based hierarchical RCU fanout value"
573 depends on TREE_RCU || PREEMPT_RCU
577 This option controls the fanout of hierarchical implementations
578 of RCU, allowing RCU to work efficiently on machines with
579 large numbers of CPUs. This value must be at least the fourth
580 root of NR_CPUS, which allows NR_CPUS to be insanely large.
581 The default value of RCU_FANOUT should be used for production
582 systems, but if you are stress-testing the RCU implementation
583 itself, small RCU_FANOUT values allow you to test large-system
584 code paths on small(er) systems.
586 Select a specific number if testing RCU itself.
587 Take the default if unsure.
589 config RCU_FANOUT_LEAF
590 int "Tree-based hierarchical RCU leaf-level fanout value"
591 range 2 RCU_FANOUT if 64BIT
592 range 2 RCU_FANOUT if !64BIT
593 depends on TREE_RCU || PREEMPT_RCU
596 This option controls the leaf-level fanout of hierarchical
597 implementations of RCU, and allows trading off cache misses
598 against lock contention. Systems that synchronize their
599 scheduling-clock interrupts for energy-efficiency reasons will
600 want the default because the smaller leaf-level fanout keeps
601 lock contention levels acceptably low. Very large systems
602 (hundreds or thousands of CPUs) will instead want to set this
603 value to the maximum value possible in order to reduce the
604 number of cache misses incurred during RCU's grace-period
605 initialization. These systems tend to run CPU-bound, and thus
606 are not helped by synchronized interrupts, and thus tend to
607 skew them, which reduces lock contention enough that large
608 leaf-level fanouts work well.
610 Select a specific number if testing RCU itself.
612 Select the maximum permissible value for large systems.
614 Take the default if unsure.
616 config RCU_FANOUT_EXACT
617 bool "Disable tree-based hierarchical RCU auto-balancing"
618 depends on TREE_RCU || PREEMPT_RCU
621 This option forces use of the exact RCU_FANOUT value specified,
622 regardless of imbalances in the hierarchy. This is useful for
623 testing RCU itself, and might one day be useful on systems with
624 strong NUMA behavior.
626 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
630 config RCU_FAST_NO_HZ
631 bool "Accelerate last non-dyntick-idle CPU's grace periods"
632 depends on NO_HZ_COMMON && SMP
635 This option permits CPUs to enter dynticks-idle state even if
636 they have RCU callbacks queued, and prevents RCU from waking
637 these CPUs up more than roughly once every four jiffies (by
638 default, you can adjust this using the rcutree.rcu_idle_gp_delay
639 parameter), thus improving energy efficiency. On the other
640 hand, this option increases the duration of RCU grace periods,
641 for example, slowing down synchronize_rcu().
643 Say Y if energy efficiency is critically important, and you
644 don't care about increased grace-period durations.
646 Say N if you are unsure.
648 config TREE_RCU_TRACE
649 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
652 This option provides tracing for the TREE_RCU and
653 PREEMPT_RCU implementations, permitting Makefile to
654 trivially select kernel/rcutree_trace.c.
657 bool "Enable RCU priority boosting"
658 depends on RT_MUTEXES && PREEMPT_RCU
661 This option boosts the priority of preempted RCU readers that
662 block the current preemptible RCU grace period for too long.
663 This option also prevents heavy loads from blocking RCU
664 callback invocation for all flavors of RCU.
666 Say Y here if you are working with real-time apps or heavy loads
667 Say N here if you are unsure.
669 config RCU_KTHREAD_PRIO
670 int "Real-time priority to use for RCU worker threads"
675 This option specifies the SCHED_FIFO priority value that will be
676 assigned to the rcuc/n and rcub/n threads and is also the value
677 used for RCU_BOOST (if enabled). If you are working with a
678 real-time application that has one or more CPU-bound threads
679 running at a real-time priority level, you should set
680 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
681 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
682 value of 1 is appropriate in the common case, which is real-time
683 applications that do not have any CPU-bound threads.
685 Some real-time applications might not have a single real-time
686 thread that saturates a given CPU, but instead might have
687 multiple real-time threads that, taken together, fully utilize
688 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
689 a priority higher than the lowest-priority thread that is
690 conspiring to prevent the CPU from running any non-real-time
691 tasks. For example, if one thread at priority 10 and another
692 thread at priority 5 are between themselves fully consuming
693 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
694 set to priority 6 or higher.
696 Specify the real-time priority, or take the default if unsure.
698 config RCU_BOOST_DELAY
699 int "Milliseconds to delay boosting after RCU grace-period start"
704 This option specifies the time to wait after the beginning of
705 a given grace period before priority-boosting preempted RCU
706 readers blocking that grace period. Note that any RCU reader
707 blocking an expedited RCU grace period is boosted immediately.
709 Accept the default if unsure.
712 bool "Offload RCU callback processing from boot-selected CPUs"
713 depends on TREE_RCU || PREEMPT_RCU
716 Use this option to reduce OS jitter for aggressive HPC or
717 real-time workloads. It can also be used to offload RCU
718 callback invocation to energy-efficient CPUs in battery-powered
719 asymmetric multiprocessors.
721 This option offloads callback invocation from the set of
722 CPUs specified at boot time by the rcu_nocbs parameter.
723 For each such CPU, a kthread ("rcuox/N") will be created to
724 invoke callbacks, where the "N" is the CPU being offloaded,
725 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
726 "s" for RCU-sched. Nothing prevents this kthread from running
727 on the specified CPUs, but (1) the kthreads may be preempted
728 between each callback, and (2) affinity or cgroups can be used
729 to force the kthreads to run on whatever set of CPUs is desired.
731 Say Y here if you want to help to debug reduced OS jitter.
732 Say N here if you are unsure.
735 prompt "Build-forced no-CBs CPUs"
736 default RCU_NOCB_CPU_NONE
737 depends on RCU_NOCB_CPU
739 This option allows no-CBs CPUs (whose RCU callbacks are invoked
740 from kthreads rather than from softirq context) to be specified
741 at build time. Additional no-CBs CPUs may be specified by
742 the rcu_nocbs= boot parameter.
744 config RCU_NOCB_CPU_NONE
745 bool "No build_forced no-CBs CPUs"
747 This option does not force any of the CPUs to be no-CBs CPUs.
748 Only CPUs designated by the rcu_nocbs= boot parameter will be
749 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
750 kthreads whose names begin with "rcuo". All other CPUs will
751 invoke their own RCU callbacks in softirq context.
753 Select this option if you want to choose no-CBs CPUs at
754 boot time, for example, to allow testing of different no-CBs
755 configurations without having to rebuild the kernel each time.
757 config RCU_NOCB_CPU_ZERO
758 bool "CPU 0 is a build_forced no-CBs CPU"
760 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
761 callbacks are invoked by a per-CPU kthread whose name begins
762 with "rcuo". Additional CPUs may be designated as no-CBs
763 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
764 All other CPUs will invoke their own RCU callbacks in softirq
767 Select this if CPU 0 needs to be a no-CBs CPU for real-time
768 or energy-efficiency reasons, but the real reason it exists
769 is to ensure that randconfig testing covers mixed systems.
771 config RCU_NOCB_CPU_ALL
772 bool "All CPUs are build_forced no-CBs CPUs"
774 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
775 boot parameter will be ignored. All CPUs' RCU callbacks will
776 be executed in the context of per-CPU rcuo kthreads created for
777 this purpose. Assuming that the kthreads whose names start with
778 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
779 on the remaining CPUs, but might decrease memory locality during
780 RCU-callback invocation, thus potentially degrading throughput.
782 Select this if all CPUs need to be no-CBs CPUs for real-time
783 or energy-efficiency reasons.
787 endmenu # "RCU Subsystem"
794 tristate "Kernel .config support"
797 This option enables the complete Linux kernel ".config" file
798 contents to be saved in the kernel. It provides documentation
799 of which kernel options are used in a running kernel or in an
800 on-disk kernel. This information can be extracted from the kernel
801 image file with the script scripts/extract-ikconfig and used as
802 input to rebuild the current kernel or to build another kernel.
803 It can also be extracted from a running kernel by reading
804 /proc/config.gz if enabled (below).
807 bool "Enable access to .config through /proc/config.gz"
808 depends on IKCONFIG && PROC_FS
810 This option enables access to the kernel configuration file
811 through /proc/config.gz.
814 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
819 Select the minimal kernel log buffer size as a power of 2.
820 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
821 parameter, see below. Any higher size also might be forced
822 by "log_buf_len" boot parameter.
832 config LOG_CPU_MAX_BUF_SHIFT
833 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
836 default 12 if !BASE_SMALL
837 default 0 if BASE_SMALL
840 This option allows to increase the default ring buffer size
841 according to the number of CPUs. The value defines the contribution
842 of each CPU as a power of 2. The used space is typically only few
843 lines however it might be much more when problems are reported,
846 The increased size means that a new buffer has to be allocated and
847 the original static one is unused. It makes sense only on systems
848 with more CPUs. Therefore this value is used only when the sum of
849 contributions is greater than the half of the default kernel ring
850 buffer as defined by LOG_BUF_SHIFT. The default values are set
851 so that more than 64 CPUs are needed to trigger the allocation.
853 Also this option is ignored when "log_buf_len" kernel parameter is
854 used as it forces an exact (power of two) size of the ring buffer.
856 The number of possible CPUs is used for this computation ignoring
857 hotplugging making the compuation optimal for the the worst case
858 scenerio while allowing a simple algorithm to be used from bootup.
860 Examples shift values and their meaning:
861 17 => 128 KB for each CPU
862 16 => 64 KB for each CPU
863 15 => 32 KB for each CPU
864 14 => 16 KB for each CPU
865 13 => 8 KB for each CPU
866 12 => 4 KB for each CPU
869 # Architectures with an unreliable sched_clock() should select this:
871 config HAVE_UNSTABLE_SCHED_CLOCK
874 config GENERIC_SCHED_CLOCK
878 # For architectures that want to enable the support for NUMA-affine scheduler
881 config ARCH_SUPPORTS_NUMA_BALANCING
885 # For architectures that know their GCC __int128 support is sound
887 config ARCH_SUPPORTS_INT128
890 # For architectures that (ab)use NUMA to represent different memory regions
891 # all cpu-local but of different latencies, such as SuperH.
893 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
896 config NUMA_BALANCING
897 bool "Memory placement aware NUMA scheduler"
898 depends on ARCH_SUPPORTS_NUMA_BALANCING
899 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
900 depends on SMP && NUMA && MIGRATION
902 This option adds support for automatic NUMA aware memory/task placement.
903 The mechanism is quite primitive and is based on migrating memory when
904 it has references to the node the task is running on.
906 This system will be inactive on UMA systems.
908 config NUMA_BALANCING_DEFAULT_ENABLED
909 bool "Automatically enable NUMA aware memory/task placement"
911 depends on NUMA_BALANCING
913 If set, automatic NUMA balancing will be enabled if running on a NUMA
917 boolean "Control Group support"
920 This option adds support for grouping sets of processes together, for
921 use with process control subsystems such as Cpusets, CFS, memory
922 controls or device isolation.
924 - Documentation/scheduler/sched-design-CFS.txt (CFS)
925 - Documentation/cgroups/ (features for grouping, isolation
926 and resource control)
933 bool "Example debug cgroup subsystem"
936 This option enables a simple cgroup subsystem that
937 exports useful debugging information about the cgroups
942 config CGROUP_FREEZER
943 bool "Freezer cgroup subsystem"
945 Provides a way to freeze and unfreeze all tasks in a
949 bool "Device controller for cgroups"
951 Provides a cgroup implementing whitelists for devices which
952 a process in the cgroup can mknod or open.
955 bool "Cpuset support"
957 This option will let you create and manage CPUSETs which
958 allow dynamically partitioning a system into sets of CPUs and
959 Memory Nodes and assigning tasks to run only within those sets.
960 This is primarily useful on large SMP or NUMA systems.
964 config PROC_PID_CPUSET
965 bool "Include legacy /proc/<pid>/cpuset file"
969 config CGROUP_CPUACCT
970 bool "Simple CPU accounting cgroup subsystem"
972 Provides a simple Resource Controller for monitoring the
973 total CPU consumed by the tasks in a cgroup.
979 bool "Memory Resource Controller for Control Groups"
983 Provides a memory resource controller that manages both anonymous
984 memory and page cache. (See Documentation/cgroups/memory.txt)
987 bool "Memory Resource Controller Swap Extension"
988 depends on MEMCG && SWAP
990 Add swap management feature to memory resource controller. When you
991 enable this, you can limit mem+swap usage per cgroup. In other words,
992 when you disable this, memory resource controller has no cares to
993 usage of swap...a process can exhaust all of the swap. This extension
994 is useful when you want to avoid exhaustion swap but this itself
995 adds more overheads and consumes memory for remembering information.
996 Especially if you use 32bit system or small memory system, please
997 be careful about enabling this. When memory resource controller
998 is disabled by boot option, this will be automatically disabled and
999 there will be no overhead from this. Even when you set this config=y,
1000 if boot option "swapaccount=0" is set, swap will not be accounted.
1001 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1002 size is 4096bytes, 512k per 1Gbytes of swap.
1003 config MEMCG_SWAP_ENABLED
1004 bool "Memory Resource Controller Swap Extension enabled by default"
1005 depends on MEMCG_SWAP
1008 Memory Resource Controller Swap Extension comes with its price in
1009 a bigger memory consumption. General purpose distribution kernels
1010 which want to enable the feature but keep it disabled by default
1011 and let the user enable it by swapaccount=1 boot command line
1012 parameter should have this option unselected.
1013 For those who want to have the feature enabled by default should
1014 select this option (if, for some reason, they need to disable it
1015 then swapaccount=0 does the trick).
1017 bool "Memory Resource Controller Kernel Memory accounting"
1019 depends on SLUB || SLAB
1021 The Kernel Memory extension for Memory Resource Controller can limit
1022 the amount of memory used by kernel objects in the system. Those are
1023 fundamentally different from the entities handled by the standard
1024 Memory Controller, which are page-based, and can be swapped. Users of
1025 the kmem extension can use it to guarantee that no group of processes
1026 will ever exhaust kernel resources alone.
1028 WARNING: Current implementation lacks reclaim support. That means
1029 allocation attempts will fail when close to the limit even if there
1030 are plenty of kmem available for reclaim. That makes this option
1031 unusable in real life so DO NOT SELECT IT unless for development
1034 config CGROUP_HUGETLB
1035 bool "HugeTLB Resource Controller for Control Groups"
1036 depends on HUGETLB_PAGE
1040 Provides a cgroup Resource Controller for HugeTLB pages.
1041 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1042 The limit is enforced during page fault. Since HugeTLB doesn't
1043 support page reclaim, enforcing the limit at page fault time implies
1044 that, the application will get SIGBUS signal if it tries to access
1045 HugeTLB pages beyond its limit. This requires the application to know
1046 beforehand how much HugeTLB pages it would require for its use. The
1047 control group is tracked in the third page lru pointer. This means
1048 that we cannot use the controller with huge page less than 3 pages.
1051 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1052 depends on PERF_EVENTS && CGROUPS
1054 This option extends the per-cpu mode to restrict monitoring to
1055 threads which belong to the cgroup specified and run on the
1060 menuconfig CGROUP_SCHED
1061 bool "Group CPU scheduler"
1064 This feature lets CPU scheduler recognize task groups and control CPU
1065 bandwidth allocation to such task groups. It uses cgroups to group
1069 config FAIR_GROUP_SCHED
1070 bool "Group scheduling for SCHED_OTHER"
1071 depends on CGROUP_SCHED
1072 default CGROUP_SCHED
1074 config CFS_BANDWIDTH
1075 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1076 depends on FAIR_GROUP_SCHED
1079 This option allows users to define CPU bandwidth rates (limits) for
1080 tasks running within the fair group scheduler. Groups with no limit
1081 set are considered to be unconstrained and will run with no
1083 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1085 config RT_GROUP_SCHED
1086 bool "Group scheduling for SCHED_RR/FIFO"
1087 depends on CGROUP_SCHED
1090 This feature lets you explicitly allocate real CPU bandwidth
1091 to task groups. If enabled, it will also make it impossible to
1092 schedule realtime tasks for non-root users until you allocate
1093 realtime bandwidth for them.
1094 See Documentation/scheduler/sched-rt-group.txt for more information.
1099 bool "Block IO controller"
1103 Generic block IO controller cgroup interface. This is the common
1104 cgroup interface which should be used by various IO controlling
1107 Currently, CFQ IO scheduler uses it to recognize task groups and
1108 control disk bandwidth allocation (proportional time slice allocation)
1109 to such task groups. It is also used by bio throttling logic in
1110 block layer to implement upper limit in IO rates on a device.
1112 This option only enables generic Block IO controller infrastructure.
1113 One needs to also enable actual IO controlling logic/policy. For
1114 enabling proportional weight division of disk bandwidth in CFQ, set
1115 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1116 CONFIG_BLK_DEV_THROTTLING=y.
1118 See Documentation/cgroups/blkio-controller.txt for more information.
1120 config DEBUG_BLK_CGROUP
1121 bool "Enable Block IO controller debugging"
1122 depends on BLK_CGROUP
1125 Enable some debugging help. Currently it exports additional stat
1126 files in a cgroup which can be useful for debugging.
1130 config CHECKPOINT_RESTORE
1131 bool "Checkpoint/restore support" if EXPERT
1134 Enables additional kernel features in a sake of checkpoint/restore.
1135 In particular it adds auxiliary prctl codes to setup process text,
1136 data and heap segment sizes, and a few additional /proc filesystem
1139 If unsure, say N here.
1141 menuconfig NAMESPACES
1142 bool "Namespaces support" if EXPERT
1145 Provides the way to make tasks work with different objects using
1146 the same id. For example same IPC id may refer to different objects
1147 or same user id or pid may refer to different tasks when used in
1148 different namespaces.
1153 bool "UTS namespace"
1156 In this namespace tasks see different info provided with the
1160 bool "IPC namespace"
1161 depends on (SYSVIPC || POSIX_MQUEUE)
1164 In this namespace tasks work with IPC ids which correspond to
1165 different IPC objects in different namespaces.
1168 bool "User namespace"
1171 This allows containers, i.e. vservers, to use user namespaces
1172 to provide different user info for different servers.
1174 When user namespaces are enabled in the kernel it is
1175 recommended that the MEMCG and MEMCG_KMEM options also be
1176 enabled and that user-space use the memory control groups to
1177 limit the amount of memory a memory unprivileged users can
1183 bool "PID Namespaces"
1186 Support process id namespaces. This allows having multiple
1187 processes with the same pid as long as they are in different
1188 pid namespaces. This is a building block of containers.
1191 bool "Network namespace"
1195 Allow user space to create what appear to be multiple instances
1196 of the network stack.
1200 config SCHED_AUTOGROUP
1201 bool "Automatic process group scheduling"
1204 select FAIR_GROUP_SCHED
1206 This option optimizes the scheduler for common desktop workloads by
1207 automatically creating and populating task groups. This separation
1208 of workloads isolates aggressive CPU burners (like build jobs) from
1209 desktop applications. Task group autogeneration is currently based
1212 config SYSFS_DEPRECATED
1213 bool "Enable deprecated sysfs features to support old userspace tools"
1217 This option adds code that switches the layout of the "block" class
1218 devices, to not show up in /sys/class/block/, but only in
1221 This switch is only active when the sysfs.deprecated=1 boot option is
1222 passed or the SYSFS_DEPRECATED_V2 option is set.
1224 This option allows new kernels to run on old distributions and tools,
1225 which might get confused by /sys/class/block/. Since 2007/2008 all
1226 major distributions and tools handle this just fine.
1228 Recent distributions and userspace tools after 2009/2010 depend on
1229 the existence of /sys/class/block/, and will not work with this
1232 Only if you are using a new kernel on an old distribution, you might
1235 config SYSFS_DEPRECATED_V2
1236 bool "Enable deprecated sysfs features by default"
1239 depends on SYSFS_DEPRECATED
1241 Enable deprecated sysfs by default.
1243 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1246 Only if you are using a new kernel on an old distribution, you might
1247 need to say Y here. Even then, odds are you would not need it
1248 enabled, you can always pass the boot option if absolutely necessary.
1251 bool "Kernel->user space relay support (formerly relayfs)"
1253 This option enables support for relay interface support in
1254 certain file systems (such as debugfs).
1255 It is designed to provide an efficient mechanism for tools and
1256 facilities to relay large amounts of data from kernel space to
1261 config BLK_DEV_INITRD
1262 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1263 depends on BROKEN || !FRV
1265 The initial RAM filesystem is a ramfs which is loaded by the
1266 boot loader (loadlin or lilo) and that is mounted as root
1267 before the normal boot procedure. It is typically used to
1268 load modules needed to mount the "real" root file system,
1269 etc. See <file:Documentation/initrd.txt> for details.
1271 If RAM disk support (BLK_DEV_RAM) is also included, this
1272 also enables initial RAM disk (initrd) support and adds
1273 15 Kbytes (more on some other architectures) to the kernel size.
1279 source "usr/Kconfig"
1283 config INIT_FALLBACK
1284 bool "Fall back to defaults if init= parameter is bad"
1287 If enabled, the kernel will try the default init binaries if an
1288 explicit request from the init= parameter fails.
1290 This can have unexpected effects. For example, booting
1291 with init=/sbin/kiosk_app will run /sbin/init or even /bin/sh
1292 if /sbin/kiosk_app cannot be executed.
1294 The default value of Y is consistent with historical behavior.
1295 Selecting N is likely to be more appropriate for most uses,
1296 especially on kiosks and on kernels that are intended to be
1297 run under the control of a script.
1299 config CC_OPTIMIZE_FOR_SIZE
1300 bool "Optimize for size"
1302 Enabling this option will pass "-Os" instead of "-O2" to gcc
1303 resulting in a smaller kernel.
1316 config SYSCTL_EXCEPTION_TRACE
1319 Enable support for /proc/sys/debug/exception-trace.
1321 config SYSCTL_ARCH_UNALIGN_NO_WARN
1324 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1325 Allows arch to define/use @no_unaligned_warning to possibly warn
1326 about unaligned access emulation going on under the hood.
1328 config SYSCTL_ARCH_UNALIGN_ALLOW
1331 Enable support for /proc/sys/kernel/unaligned-trap
1332 Allows arches to define/use @unaligned_enabled to runtime toggle
1333 the unaligned access emulation.
1334 see arch/parisc/kernel/unaligned.c for reference
1336 config HAVE_PCSPKR_PLATFORM
1339 # interpreter that classic socket filters depend on
1344 bool "Configure standard kernel features (expert users)"
1345 # Unhide debug options, to make the on-by-default options visible
1348 This option allows certain base kernel options and settings
1349 to be disabled or tweaked. This is for specialized
1350 environments which can tolerate a "non-standard" kernel.
1351 Only use this if you really know what you are doing.
1354 bool "Enable 16-bit UID system calls" if EXPERT
1355 depends on HAVE_UID16
1358 This enables the legacy 16-bit UID syscall wrappers.
1360 config SGETMASK_SYSCALL
1361 bool "sgetmask/ssetmask syscalls support" if EXPERT
1362 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1364 sys_sgetmask and sys_ssetmask are obsolete system calls
1365 no longer supported in libc but still enabled by default in some
1368 If unsure, leave the default option here.
1370 config SYSFS_SYSCALL
1371 bool "Sysfs syscall support" if EXPERT
1374 sys_sysfs is an obsolete system call no longer supported in libc.
1375 Note that disabling this option is more secure but might break
1376 compatibility with some systems.
1378 If unsure say Y here.
1380 config SYSCTL_SYSCALL
1381 bool "Sysctl syscall support" if EXPERT
1382 depends on PROC_SYSCTL
1386 sys_sysctl uses binary paths that have been found challenging
1387 to properly maintain and use. The interface in /proc/sys
1388 using paths with ascii names is now the primary path to this
1391 Almost nothing using the binary sysctl interface so if you are
1392 trying to save some space it is probably safe to disable this,
1393 making your kernel marginally smaller.
1395 If unsure say N here.
1398 bool "Load all symbols for debugging/ksymoops" if EXPERT
1401 Say Y here to let the kernel print out symbolic crash information and
1402 symbolic stack backtraces. This increases the size of the kernel
1403 somewhat, as all symbols have to be loaded into the kernel image.
1406 bool "Include all symbols in kallsyms"
1407 depends on DEBUG_KERNEL && KALLSYMS
1409 Normally kallsyms only contains the symbols of functions for nicer
1410 OOPS messages and backtraces (i.e., symbols from the text and inittext
1411 sections). This is sufficient for most cases. And only in very rare
1412 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1413 names of variables from the data sections, etc).
1415 This option makes sure that all symbols are loaded into the kernel
1416 image (i.e., symbols from all sections) in cost of increased kernel
1417 size (depending on the kernel configuration, it may be 300KiB or
1418 something like this).
1420 Say N unless you really need all symbols.
1424 bool "Enable support for printk" if EXPERT
1427 This option enables normal printk support. Removing it
1428 eliminates most of the message strings from the kernel image
1429 and makes the kernel more or less silent. As this makes it
1430 very difficult to diagnose system problems, saying N here is
1431 strongly discouraged.
1434 bool "BUG() support" if EXPERT
1437 Disabling this option eliminates support for BUG and WARN, reducing
1438 the size of your kernel image and potentially quietly ignoring
1439 numerous fatal conditions. You should only consider disabling this
1440 option for embedded systems with no facilities for reporting errors.
1446 bool "Enable ELF core dumps" if EXPERT
1448 Enable support for generating core dumps. Disabling saves about 4k.
1451 config PCSPKR_PLATFORM
1452 bool "Enable PC-Speaker support" if EXPERT
1453 depends on HAVE_PCSPKR_PLATFORM
1457 This option allows to disable the internal PC-Speaker
1458 support, saving some memory.
1462 bool "Enable full-sized data structures for core" if EXPERT
1464 Disabling this option reduces the size of miscellaneous core
1465 kernel data structures. This saves memory on small machines,
1466 but may reduce performance.
1469 bool "Enable futex support" if EXPERT
1473 Disabling this option will cause the kernel to be built without
1474 support for "fast userspace mutexes". The resulting kernel may not
1475 run glibc-based applications correctly.
1477 config HAVE_FUTEX_CMPXCHG
1481 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1482 is implemented and always working. This removes a couple of runtime
1486 bool "Enable eventpoll support" if EXPERT
1490 Disabling this option will cause the kernel to be built without
1491 support for epoll family of system calls.
1494 bool "Enable signalfd() system call" if EXPERT
1498 Enable the signalfd() system call that allows to receive signals
1499 on a file descriptor.
1504 bool "Enable timerfd() system call" if EXPERT
1508 Enable the timerfd() system call that allows to receive timer
1509 events on a file descriptor.
1514 bool "Enable eventfd() system call" if EXPERT
1518 Enable the eventfd() system call that allows to receive both
1519 kernel notification (ie. KAIO) or userspace notifications.
1523 # syscall, maps, verifier
1525 bool "Enable bpf() system call" if EXPERT
1530 Enable the bpf() system call that allows to manipulate eBPF
1531 programs and maps via file descriptors.
1534 bool "Use full shmem filesystem" if EXPERT
1538 The shmem is an internal filesystem used to manage shared memory.
1539 It is backed by swap and manages resource limits. It is also exported
1540 to userspace as tmpfs if TMPFS is enabled. Disabling this
1541 option replaces shmem and tmpfs with the much simpler ramfs code,
1542 which may be appropriate on small systems without swap.
1545 bool "Enable AIO support" if EXPERT
1548 This option enables POSIX asynchronous I/O which may by used
1549 by some high performance threaded applications. Disabling
1550 this option saves about 7k.
1552 config ADVISE_SYSCALLS
1553 bool "Enable madvise/fadvise syscalls" if EXPERT
1556 This option enables the madvise and fadvise syscalls, used by
1557 applications to advise the kernel about their future memory or file
1558 usage, improving performance. If building an embedded system where no
1559 applications use these syscalls, you can disable this option to save
1564 bool "Enable PCI quirk workarounds" if EXPERT
1567 This enables workarounds for various PCI chipset
1568 bugs/quirks. Disable this only if your target machine is
1569 unaffected by PCI quirks.
1572 bool "Embedded system"
1573 option allnoconfig_y
1576 This option should be enabled if compiling the kernel for
1577 an embedded system so certain expert options are available
1580 config HAVE_PERF_EVENTS
1583 See tools/perf/design.txt for details.
1585 config PERF_USE_VMALLOC
1588 See tools/perf/design.txt for details
1590 menu "Kernel Performance Events And Counters"
1593 bool "Kernel performance events and counters"
1594 default y if PROFILING
1595 depends on HAVE_PERF_EVENTS
1599 Enable kernel support for various performance events provided
1600 by software and hardware.
1602 Software events are supported either built-in or via the
1603 use of generic tracepoints.
1605 Most modern CPUs support performance events via performance
1606 counter registers. These registers count the number of certain
1607 types of hw events: such as instructions executed, cachemisses
1608 suffered, or branches mis-predicted - without slowing down the
1609 kernel or applications. These registers can also trigger interrupts
1610 when a threshold number of events have passed - and can thus be
1611 used to profile the code that runs on that CPU.
1613 The Linux Performance Event subsystem provides an abstraction of
1614 these software and hardware event capabilities, available via a
1615 system call and used by the "perf" utility in tools/perf/. It
1616 provides per task and per CPU counters, and it provides event
1617 capabilities on top of those.
1621 config DEBUG_PERF_USE_VMALLOC
1623 bool "Debug: use vmalloc to back perf mmap() buffers"
1624 depends on PERF_EVENTS && DEBUG_KERNEL
1625 select PERF_USE_VMALLOC
1627 Use vmalloc memory to back perf mmap() buffers.
1629 Mostly useful for debugging the vmalloc code on platforms
1630 that don't require it.
1636 config VM_EVENT_COUNTERS
1638 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1640 VM event counters are needed for event counts to be shown.
1641 This option allows the disabling of the VM event counters
1642 on EXPERT systems. /proc/vmstat will only show page counts
1643 if VM event counters are disabled.
1647 bool "Enable SLUB debugging support" if EXPERT
1648 depends on SLUB && SYSFS
1650 SLUB has extensive debug support features. Disabling these can
1651 result in significant savings in code size. This also disables
1652 SLUB sysfs support. /sys/slab will not exist and there will be
1653 no support for cache validation etc.
1656 bool "Disable heap randomization"
1659 Randomizing heap placement makes heap exploits harder, but it
1660 also breaks ancient binaries (including anything libc5 based).
1661 This option changes the bootup default to heap randomization
1662 disabled, and can be overridden at runtime by setting
1663 /proc/sys/kernel/randomize_va_space to 2.
1665 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1668 prompt "Choose SLAB allocator"
1671 This option allows to select a slab allocator.
1676 The regular slab allocator that is established and known to work
1677 well in all environments. It organizes cache hot objects in
1678 per cpu and per node queues.
1681 bool "SLUB (Unqueued Allocator)"
1683 SLUB is a slab allocator that minimizes cache line usage
1684 instead of managing queues of cached objects (SLAB approach).
1685 Per cpu caching is realized using slabs of objects instead
1686 of queues of objects. SLUB can use memory efficiently
1687 and has enhanced diagnostics. SLUB is the default choice for
1692 bool "SLOB (Simple Allocator)"
1694 SLOB replaces the stock allocator with a drastically simpler
1695 allocator. SLOB is generally more space efficient but
1696 does not perform as well on large systems.
1700 config SLUB_CPU_PARTIAL
1702 depends on SLUB && SMP
1703 bool "SLUB per cpu partial cache"
1705 Per cpu partial caches accellerate objects allocation and freeing
1706 that is local to a processor at the price of more indeterminism
1707 in the latency of the free. On overflow these caches will be cleared
1708 which requires the taking of locks that may cause latency spikes.
1709 Typically one would choose no for a realtime system.
1711 config MMAP_ALLOW_UNINITIALIZED
1712 bool "Allow mmapped anonymous memory to be uninitialized"
1713 depends on EXPERT && !MMU
1716 Normally, and according to the Linux spec, anonymous memory obtained
1717 from mmap() has it's contents cleared before it is passed to
1718 userspace. Enabling this config option allows you to request that
1719 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1720 providing a huge performance boost. If this option is not enabled,
1721 then the flag will be ignored.
1723 This is taken advantage of by uClibc's malloc(), and also by
1724 ELF-FDPIC binfmt's brk and stack allocator.
1726 Because of the obvious security issues, this option should only be
1727 enabled on embedded devices where you control what is run in
1728 userspace. Since that isn't generally a problem on no-MMU systems,
1729 it is normally safe to say Y here.
1731 See Documentation/nommu-mmap.txt for more information.
1733 config SYSTEM_TRUSTED_KEYRING
1734 bool "Provide system-wide ring of trusted keys"
1737 Provide a system keyring to which trusted keys can be added. Keys in
1738 the keyring are considered to be trusted. Keys may be added at will
1739 by the kernel from compiled-in data and from hardware key stores, but
1740 userspace may only add extra keys if those keys can be verified by
1741 keys already in the keyring.
1743 Keys in this keyring are used by module signature checking.
1746 bool "Profiling support"
1748 Say Y here to enable the extended profiling support mechanisms used
1749 by profilers such as OProfile.
1752 # Place an empty function call at each tracepoint site. Can be
1753 # dynamically changed for a probe function.
1758 source "arch/Kconfig"
1760 endmenu # General setup
1762 config HAVE_GENERIC_DMA_COHERENT
1769 depends on SLAB || SLUB_DEBUG
1777 default 0 if BASE_FULL
1778 default 1 if !BASE_FULL
1781 bool "Enable loadable module support"
1784 Kernel modules are small pieces of compiled code which can
1785 be inserted in the running kernel, rather than being
1786 permanently built into the kernel. You use the "modprobe"
1787 tool to add (and sometimes remove) them. If you say Y here,
1788 many parts of the kernel can be built as modules (by
1789 answering M instead of Y where indicated): this is most
1790 useful for infrequently used options which are not required
1791 for booting. For more information, see the man pages for
1792 modprobe, lsmod, modinfo, insmod and rmmod.
1794 If you say Y here, you will need to run "make
1795 modules_install" to put the modules under /lib/modules/
1796 where modprobe can find them (you may need to be root to do
1803 config MODULE_FORCE_LOAD
1804 bool "Forced module loading"
1807 Allow loading of modules without version information (ie. modprobe
1808 --force). Forced module loading sets the 'F' (forced) taint flag and
1809 is usually a really bad idea.
1811 config MODULE_UNLOAD
1812 bool "Module unloading"
1814 Without this option you will not be able to unload any
1815 modules (note that some modules may not be unloadable
1816 anyway), which makes your kernel smaller, faster
1817 and simpler. If unsure, say Y.
1819 config MODULE_FORCE_UNLOAD
1820 bool "Forced module unloading"
1821 depends on MODULE_UNLOAD
1823 This option allows you to force a module to unload, even if the
1824 kernel believes it is unsafe: the kernel will remove the module
1825 without waiting for anyone to stop using it (using the -f option to
1826 rmmod). This is mainly for kernel developers and desperate users.
1830 bool "Module versioning support"
1832 Usually, you have to use modules compiled with your kernel.
1833 Saying Y here makes it sometimes possible to use modules
1834 compiled for different kernels, by adding enough information
1835 to the modules to (hopefully) spot any changes which would
1836 make them incompatible with the kernel you are running. If
1839 config MODULE_SRCVERSION_ALL
1840 bool "Source checksum for all modules"
1842 Modules which contain a MODULE_VERSION get an extra "srcversion"
1843 field inserted into their modinfo section, which contains a
1844 sum of the source files which made it. This helps maintainers
1845 see exactly which source was used to build a module (since
1846 others sometimes change the module source without updating
1847 the version). With this option, such a "srcversion" field
1848 will be created for all modules. If unsure, say N.
1851 bool "Module signature verification"
1853 select SYSTEM_TRUSTED_KEYRING
1856 select ASYMMETRIC_KEY_TYPE
1857 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1858 select PUBLIC_KEY_ALGO_RSA
1861 select X509_CERTIFICATE_PARSER
1863 Check modules for valid signatures upon load: the signature
1864 is simply appended to the module. For more information see
1865 Documentation/module-signing.txt.
1867 !!!WARNING!!! If you enable this option, you MUST make sure that the
1868 module DOES NOT get stripped after being signed. This includes the
1869 debuginfo strip done by some packagers (such as rpmbuild) and
1870 inclusion into an initramfs that wants the module size reduced.
1872 config MODULE_SIG_FORCE
1873 bool "Require modules to be validly signed"
1874 depends on MODULE_SIG
1876 Reject unsigned modules or signed modules for which we don't have a
1877 key. Without this, such modules will simply taint the kernel.
1879 config MODULE_SIG_ALL
1880 bool "Automatically sign all modules"
1882 depends on MODULE_SIG
1884 Sign all modules during make modules_install. Without this option,
1885 modules must be signed manually, using the scripts/sign-file tool.
1887 comment "Do not forget to sign required modules with scripts/sign-file"
1888 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1891 prompt "Which hash algorithm should modules be signed with?"
1892 depends on MODULE_SIG
1894 This determines which sort of hashing algorithm will be used during
1895 signature generation. This algorithm _must_ be built into the kernel
1896 directly so that signature verification can take place. It is not
1897 possible to load a signed module containing the algorithm to check
1898 the signature on that module.
1900 config MODULE_SIG_SHA1
1901 bool "Sign modules with SHA-1"
1904 config MODULE_SIG_SHA224
1905 bool "Sign modules with SHA-224"
1906 select CRYPTO_SHA256
1908 config MODULE_SIG_SHA256
1909 bool "Sign modules with SHA-256"
1910 select CRYPTO_SHA256
1912 config MODULE_SIG_SHA384
1913 bool "Sign modules with SHA-384"
1914 select CRYPTO_SHA512
1916 config MODULE_SIG_SHA512
1917 bool "Sign modules with SHA-512"
1918 select CRYPTO_SHA512
1922 config MODULE_SIG_HASH
1924 depends on MODULE_SIG
1925 default "sha1" if MODULE_SIG_SHA1
1926 default "sha224" if MODULE_SIG_SHA224
1927 default "sha256" if MODULE_SIG_SHA256
1928 default "sha384" if MODULE_SIG_SHA384
1929 default "sha512" if MODULE_SIG_SHA512
1931 config MODULE_COMPRESS
1932 bool "Compress modules on installation"
1935 This option compresses the kernel modules when 'make
1936 modules_install' is run.
1938 The modules will be compressed either using gzip or xz depend on the
1939 choice made in "Compression algorithm".
1941 module-init-tools has support for gzip format while kmod handle gzip
1942 and xz compressed modules.
1944 When a kernel module is installed from outside of the main kernel
1945 source and uses the Kbuild system for installing modules then that
1946 kernel module will also be compressed when it is installed.
1948 This option provides little benefit when the modules are to be used inside
1949 an initrd or initramfs, it generally is more efficient to compress the whole
1950 initrd or initramfs instead.
1952 This is fully compatible with signed modules while the signed module is
1953 compressed. module-init-tools or kmod handles decompression and provide to
1954 other layer the uncompressed but signed payload.
1957 prompt "Compression algorithm"
1958 depends on MODULE_COMPRESS
1959 default MODULE_COMPRESS_GZIP
1961 This determines which sort of compression will be used during
1962 'make modules_install'.
1964 GZIP (default) and XZ are supported.
1966 config MODULE_COMPRESS_GZIP
1969 config MODULE_COMPRESS_XZ
1976 config INIT_ALL_POSSIBLE
1979 Back when each arch used to define their own cpu_online_mask and
1980 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1981 with all 1s, and others with all 0s. When they were centralised,
1982 it was better to provide this option than to break all the archs
1983 and have several arch maintainers pursuing me down dark alleys.
1988 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1990 Need stop_machine() primitive.
1992 source "block/Kconfig"
1994 config PREEMPT_NOTIFIERS
2001 # Can be selected by architectures with broken toolchains
2002 # that get confused by correct const<->read_only section
2004 config BROKEN_RODATA
2010 Build a simple ASN.1 grammar compiler that produces a bytecode output
2011 that can be interpreted by the ASN.1 stream decoder and used to
2012 inform it as to what tags are to be expected in a stream and what
2013 functions to call on what tags.
2015 source "kernel/Kconfig.locks"
projects / deliverable / linux.git / blob