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" if EXPERT
279 If you say Y here, a user level program will be able to map
280 file names to handle and then later use the handle for
281 different file system operations. This is useful in implementing
282 userspace file servers, which now track files using handles instead
283 of names. The handle would remain the same even if file names
284 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
288 bool "uselib syscall"
289 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
291 This option enables the uselib syscall, a system call used in the
292 dynamic linker from libc5 and earlier. glibc does not use this
293 system call. If you intend to run programs built on libc5 or
294 earlier, you may need to enable this syscall. Current systems
295 running glibc can safely disable this.
298 bool "Auditing support"
301 Enable auditing infrastructure that can be used with another
302 kernel subsystem, such as SELinux (which requires this for
303 logging of avc messages output). System call auditing is included
304 on architectures which support it.
306 config HAVE_ARCH_AUDITSYSCALL
311 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
315 depends on AUDITSYSCALL
320 depends on AUDITSYSCALL
323 source "kernel/irq/Kconfig"
324 source "kernel/time/Kconfig"
326 menu "CPU/Task time and stats accounting"
328 config VIRT_CPU_ACCOUNTING
332 prompt "Cputime accounting"
333 default TICK_CPU_ACCOUNTING if !PPC64
334 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
336 # Kind of a stub config for the pure tick based cputime accounting
337 config TICK_CPU_ACCOUNTING
338 bool "Simple tick based cputime accounting"
339 depends on !S390 && !NO_HZ_FULL
341 This is the basic tick based cputime accounting that maintains
342 statistics about user, system and idle time spent on per jiffies
347 config VIRT_CPU_ACCOUNTING_NATIVE
348 bool "Deterministic task and CPU time accounting"
349 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
350 select VIRT_CPU_ACCOUNTING
352 Select this option to enable more accurate task and CPU time
353 accounting. This is done by reading a CPU counter on each
354 kernel entry and exit and on transitions within the kernel
355 between system, softirq and hardirq state, so there is a
356 small performance impact. In the case of s390 or IBM POWER > 5,
357 this also enables accounting of stolen time on logically-partitioned
360 config VIRT_CPU_ACCOUNTING_GEN
361 bool "Full dynticks CPU time accounting"
362 depends on HAVE_CONTEXT_TRACKING
363 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
364 select VIRT_CPU_ACCOUNTING
365 select CONTEXT_TRACKING
367 Select this option to enable task and CPU time accounting on full
368 dynticks systems. This accounting is implemented by watching every
369 kernel-user boundaries using the context tracking subsystem.
370 The accounting is thus performed at the expense of some significant
373 For now this is only useful if you are working on the full
374 dynticks subsystem development.
380 config IRQ_TIME_ACCOUNTING
381 bool "Fine granularity task level IRQ time accounting"
382 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
384 Select this option to enable fine granularity task irq time
385 accounting. This is done by reading a timestamp on each
386 transitions between softirq and hardirq state, so there can be a
387 small performance impact.
389 If in doubt, say N here.
391 config BSD_PROCESS_ACCT
392 bool "BSD Process Accounting"
395 If you say Y here, a user level program will be able to instruct the
396 kernel (via a special system call) to write process accounting
397 information to a file: whenever a process exits, information about
398 that process will be appended to the file by the kernel. The
399 information includes things such as creation time, owning user,
400 command name, memory usage, controlling terminal etc. (the complete
401 list is in the struct acct in <file:include/linux/acct.h>). It is
402 up to the user level program to do useful things with this
403 information. This is generally a good idea, so say Y.
405 config BSD_PROCESS_ACCT_V3
406 bool "BSD Process Accounting version 3 file format"
407 depends on BSD_PROCESS_ACCT
410 If you say Y here, the process accounting information is written
411 in a new file format that also logs the process IDs of each
412 process and it's parent. Note that this file format is incompatible
413 with previous v0/v1/v2 file formats, so you will need updated tools
414 for processing it. A preliminary version of these tools is available
415 at <http://www.gnu.org/software/acct/>.
418 bool "Export task/process statistics through netlink"
423 Export selected statistics for tasks/processes through the
424 generic netlink interface. Unlike BSD process accounting, the
425 statistics are available during the lifetime of tasks/processes as
426 responses to commands. Like BSD accounting, they are sent to user
431 config TASK_DELAY_ACCT
432 bool "Enable per-task delay accounting"
436 Collect information on time spent by a task waiting for system
437 resources like cpu, synchronous block I/O completion and swapping
438 in pages. Such statistics can help in setting a task's priorities
439 relative to other tasks for cpu, io, rss limits etc.
444 bool "Enable extended accounting over taskstats"
447 Collect extended task accounting data and send the data
448 to userland for processing over the taskstats interface.
452 config TASK_IO_ACCOUNTING
453 bool "Enable per-task storage I/O accounting"
454 depends on TASK_XACCT
456 Collect information on the number of bytes of storage I/O which this
461 endmenu # "CPU/Task time and stats accounting"
467 default y if !PREEMPT && SMP
469 This option selects the RCU implementation that is
470 designed for very large SMP system with hundreds or
471 thousands of CPUs. It also scales down nicely to
478 This option selects the RCU implementation that is
479 designed for very large SMP systems with hundreds or
480 thousands of CPUs, but for which real-time response
481 is also required. It also scales down nicely to
484 Select this option if you are unsure.
488 default y if !PREEMPT && !SMP
490 This option selects the RCU implementation that is
491 designed for UP systems from which real-time response
492 is not required. This option greatly reduces the
493 memory footprint of RCU.
496 bool "Make expert-level adjustments to RCU configuration"
499 This option needs to be enabled if you wish to make
500 expert-level adjustments to RCU configuration. By default,
501 no such adjustments can be made, which has the often-beneficial
502 side-effect of preventing "make oldconfig" from asking you all
503 sorts of detailed questions about how you would like numerous
504 obscure RCU options to be set up.
506 Say Y if you need to make expert-level adjustments to RCU.
508 Say N if you are unsure.
513 This option selects the sleepable version of RCU. This version
514 permits arbitrary sleeping or blocking within RCU read-side critical
523 This option enables a task-based RCU implementation that uses
524 only voluntary context switch (not preemption!), idle, and
525 user-mode execution as quiescent states.
527 config RCU_STALL_COMMON
528 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
530 This option enables RCU CPU stall code that is common between
531 the TINY and TREE variants of RCU. The purpose is to allow
532 the tiny variants to disable RCU CPU stall warnings, while
533 making these warnings mandatory for the tree variants.
535 config CONTEXT_TRACKING
538 config CONTEXT_TRACKING_FORCE
539 bool "Force context tracking"
540 depends on CONTEXT_TRACKING
541 default y if !NO_HZ_FULL
543 The major pre-requirement for full dynticks to work is to
544 support the context tracking subsystem. But there are also
545 other dependencies to provide in order to make the full
548 This option stands for testing when an arch implements the
549 context tracking backend but doesn't yet fullfill all the
550 requirements to make the full dynticks feature working.
551 Without the full dynticks, there is no way to test the support
552 for context tracking and the subsystems that rely on it: RCU
553 userspace extended quiescent state and tickless cputime
554 accounting. This option copes with the absence of the full
555 dynticks subsystem by forcing the context tracking on all
558 Say Y only if you're working on the development of an
559 architecture backend for the context tracking.
561 Say N otherwise, this option brings an overhead that you
562 don't want in production.
566 int "Tree-based hierarchical RCU fanout value"
569 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
573 This option controls the fanout of hierarchical implementations
574 of RCU, allowing RCU to work efficiently on machines with
575 large numbers of CPUs. This value must be at least the fourth
576 root of NR_CPUS, which allows NR_CPUS to be insanely large.
577 The default value of RCU_FANOUT should be used for production
578 systems, but if you are stress-testing the RCU implementation
579 itself, small RCU_FANOUT values allow you to test large-system
580 code paths on small(er) systems.
582 Select a specific number if testing RCU itself.
583 Take the default if unsure.
585 config RCU_FANOUT_LEAF
586 int "Tree-based hierarchical RCU leaf-level fanout value"
589 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
592 This option controls the leaf-level fanout of hierarchical
593 implementations of RCU, and allows trading off cache misses
594 against lock contention. Systems that synchronize their
595 scheduling-clock interrupts for energy-efficiency reasons will
596 want the default because the smaller leaf-level fanout keeps
597 lock contention levels acceptably low. Very large systems
598 (hundreds or thousands of CPUs) will instead want to set this
599 value to the maximum value possible in order to reduce the
600 number of cache misses incurred during RCU's grace-period
601 initialization. These systems tend to run CPU-bound, and thus
602 are not helped by synchronized interrupts, and thus tend to
603 skew them, which reduces lock contention enough that large
604 leaf-level fanouts work well.
606 Select a specific number if testing RCU itself.
608 Select the maximum permissible value for large systems.
610 Take the default if unsure.
612 config RCU_FAST_NO_HZ
613 bool "Accelerate last non-dyntick-idle CPU's grace periods"
614 depends on NO_HZ_COMMON && SMP && RCU_EXPERT
617 This option permits CPUs to enter dynticks-idle state even if
618 they have RCU callbacks queued, and prevents RCU from waking
619 these CPUs up more than roughly once every four jiffies (by
620 default, you can adjust this using the rcutree.rcu_idle_gp_delay
621 parameter), thus improving energy efficiency. On the other
622 hand, this option increases the duration of RCU grace periods,
623 for example, slowing down synchronize_rcu().
625 Say Y if energy efficiency is critically important, and you
626 don't care about increased grace-period durations.
628 Say N if you are unsure.
630 config TREE_RCU_TRACE
631 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
634 This option provides tracing for the TREE_RCU and
635 PREEMPT_RCU implementations, permitting Makefile to
636 trivially select kernel/rcutree_trace.c.
639 bool "Enable RCU priority boosting"
640 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
643 This option boosts the priority of preempted RCU readers that
644 block the current preemptible RCU grace period for too long.
645 This option also prevents heavy loads from blocking RCU
646 callback invocation for all flavors of RCU.
648 Say Y here if you are working with real-time apps or heavy loads
649 Say N here if you are unsure.
651 config RCU_KTHREAD_PRIO
652 int "Real-time priority to use for RCU worker threads"
653 range 1 99 if RCU_BOOST
654 range 0 99 if !RCU_BOOST
655 default 1 if RCU_BOOST
656 default 0 if !RCU_BOOST
657 depends on RCU_EXPERT
659 This option specifies the SCHED_FIFO priority value that will be
660 assigned to the rcuc/n and rcub/n threads and is also the value
661 used for RCU_BOOST (if enabled). If you are working with a
662 real-time application that has one or more CPU-bound threads
663 running at a real-time priority level, you should set
664 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
665 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
666 value of 1 is appropriate in the common case, which is real-time
667 applications that do not have any CPU-bound threads.
669 Some real-time applications might not have a single real-time
670 thread that saturates a given CPU, but instead might have
671 multiple real-time threads that, taken together, fully utilize
672 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
673 a priority higher than the lowest-priority thread that is
674 conspiring to prevent the CPU from running any non-real-time
675 tasks. For example, if one thread at priority 10 and another
676 thread at priority 5 are between themselves fully consuming
677 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
678 set to priority 6 or higher.
680 Specify the real-time priority, or take the default if unsure.
682 config RCU_BOOST_DELAY
683 int "Milliseconds to delay boosting after RCU grace-period start"
688 This option specifies the time to wait after the beginning of
689 a given grace period before priority-boosting preempted RCU
690 readers blocking that grace period. Note that any RCU reader
691 blocking an expedited RCU grace period is boosted immediately.
693 Accept the default if unsure.
696 bool "Offload RCU callback processing from boot-selected CPUs"
697 depends on TREE_RCU || PREEMPT_RCU
698 depends on RCU_EXPERT || NO_HZ_FULL
701 Use this option to reduce OS jitter for aggressive HPC or
702 real-time workloads. It can also be used to offload RCU
703 callback invocation to energy-efficient CPUs in battery-powered
704 asymmetric multiprocessors.
706 This option offloads callback invocation from the set of
707 CPUs specified at boot time by the rcu_nocbs parameter.
708 For each such CPU, a kthread ("rcuox/N") will be created to
709 invoke callbacks, where the "N" is the CPU being offloaded,
710 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
711 "s" for RCU-sched. Nothing prevents this kthread from running
712 on the specified CPUs, but (1) the kthreads may be preempted
713 between each callback, and (2) affinity or cgroups can be used
714 to force the kthreads to run on whatever set of CPUs is desired.
716 Say Y here if you want to help to debug reduced OS jitter.
717 Say N here if you are unsure.
720 prompt "Build-forced no-CBs CPUs"
721 default RCU_NOCB_CPU_NONE
722 depends on RCU_NOCB_CPU
724 This option allows no-CBs CPUs (whose RCU callbacks are invoked
725 from kthreads rather than from softirq context) to be specified
726 at build time. Additional no-CBs CPUs may be specified by
727 the rcu_nocbs= boot parameter.
729 config RCU_NOCB_CPU_NONE
730 bool "No build_forced no-CBs CPUs"
732 This option does not force any of the CPUs to be no-CBs CPUs.
733 Only CPUs designated by the rcu_nocbs= boot parameter will be
734 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
735 kthreads whose names begin with "rcuo". All other CPUs will
736 invoke their own RCU callbacks in softirq context.
738 Select this option if you want to choose no-CBs CPUs at
739 boot time, for example, to allow testing of different no-CBs
740 configurations without having to rebuild the kernel each time.
742 config RCU_NOCB_CPU_ZERO
743 bool "CPU 0 is a build_forced no-CBs CPU"
745 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
746 callbacks are invoked by a per-CPU kthread whose name begins
747 with "rcuo". Additional CPUs may be designated as no-CBs
748 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
749 All other CPUs will invoke their own RCU callbacks in softirq
752 Select this if CPU 0 needs to be a no-CBs CPU for real-time
753 or energy-efficiency reasons, but the real reason it exists
754 is to ensure that randconfig testing covers mixed systems.
756 config RCU_NOCB_CPU_ALL
757 bool "All CPUs are build_forced no-CBs CPUs"
759 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
760 boot parameter will be ignored. All CPUs' RCU callbacks will
761 be executed in the context of per-CPU rcuo kthreads created for
762 this purpose. Assuming that the kthreads whose names start with
763 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
764 on the remaining CPUs, but might decrease memory locality during
765 RCU-callback invocation, thus potentially degrading throughput.
767 Select this if all CPUs need to be no-CBs CPUs for real-time
768 or energy-efficiency reasons.
772 config RCU_EXPEDITE_BOOT
776 This option enables expedited grace periods at boot time,
777 as if rcu_expedite_gp() had been invoked early in boot.
778 The corresponding rcu_unexpedite_gp() is invoked from
779 rcu_end_inkernel_boot(), which is intended to be invoked
780 at the end of the kernel-only boot sequence, just before
783 Accept the default if unsure.
785 endmenu # "RCU Subsystem"
792 tristate "Kernel .config support"
795 This option enables the complete Linux kernel ".config" file
796 contents to be saved in the kernel. It provides documentation
797 of which kernel options are used in a running kernel or in an
798 on-disk kernel. This information can be extracted from the kernel
799 image file with the script scripts/extract-ikconfig and used as
800 input to rebuild the current kernel or to build another kernel.
801 It can also be extracted from a running kernel by reading
802 /proc/config.gz if enabled (below).
805 bool "Enable access to .config through /proc/config.gz"
806 depends on IKCONFIG && PROC_FS
808 This option enables access to the kernel configuration file
809 through /proc/config.gz.
812 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
817 Select the minimal kernel log buffer size as a power of 2.
818 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
819 parameter, see below. Any higher size also might be forced
820 by "log_buf_len" boot parameter.
830 config LOG_CPU_MAX_BUF_SHIFT
831 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
834 default 12 if !BASE_SMALL
835 default 0 if BASE_SMALL
838 This option allows to increase the default ring buffer size
839 according to the number of CPUs. The value defines the contribution
840 of each CPU as a power of 2. The used space is typically only few
841 lines however it might be much more when problems are reported,
844 The increased size means that a new buffer has to be allocated and
845 the original static one is unused. It makes sense only on systems
846 with more CPUs. Therefore this value is used only when the sum of
847 contributions is greater than the half of the default kernel ring
848 buffer as defined by LOG_BUF_SHIFT. The default values are set
849 so that more than 64 CPUs are needed to trigger the allocation.
851 Also this option is ignored when "log_buf_len" kernel parameter is
852 used as it forces an exact (power of two) size of the ring buffer.
854 The number of possible CPUs is used for this computation ignoring
855 hotplugging making the compuation optimal for the the worst case
856 scenerio while allowing a simple algorithm to be used from bootup.
858 Examples shift values and their meaning:
859 17 => 128 KB for each CPU
860 16 => 64 KB for each CPU
861 15 => 32 KB for each CPU
862 14 => 16 KB for each CPU
863 13 => 8 KB for each CPU
864 12 => 4 KB for each CPU
866 config NMI_LOG_BUF_SHIFT
867 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
870 depends on PRINTK_NMI
872 Select the size of a per-CPU buffer where NMI messages are temporary
873 stored. They are copied to the main log buffer in a safe context
874 to avoid a deadlock. The value defines the size as a power of 2.
876 NMI messages are rare and limited. The largest one is when
877 a backtrace is printed. It usually fits into 4KB. Select
878 8KB if you want to be on the safe side.
881 17 => 128 KB for each CPU
882 16 => 64 KB for each CPU
883 15 => 32 KB for each CPU
884 14 => 16 KB for each CPU
885 13 => 8 KB for each CPU
886 12 => 4 KB for each CPU
889 # Architectures with an unreliable sched_clock() should select this:
891 config HAVE_UNSTABLE_SCHED_CLOCK
894 config GENERIC_SCHED_CLOCK
898 # For architectures that want to enable the support for NUMA-affine scheduler
901 config ARCH_SUPPORTS_NUMA_BALANCING
905 # For architectures that prefer to flush all TLBs after a number of pages
906 # are unmapped instead of sending one IPI per page to flush. The architecture
907 # must provide guarantees on what happens if a clean TLB cache entry is
908 # written after the unmap. Details are in mm/rmap.c near the check for
909 # should_defer_flush. The architecture should also consider if the full flush
910 # and the refill costs are offset by the savings of sending fewer IPIs.
911 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
915 # For architectures that know their GCC __int128 support is sound
917 config ARCH_SUPPORTS_INT128
920 # For architectures that (ab)use NUMA to represent different memory regions
921 # all cpu-local but of different latencies, such as SuperH.
923 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
926 config NUMA_BALANCING
927 bool "Memory placement aware NUMA scheduler"
928 depends on ARCH_SUPPORTS_NUMA_BALANCING
929 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
930 depends on SMP && NUMA && MIGRATION
932 This option adds support for automatic NUMA aware memory/task placement.
933 The mechanism is quite primitive and is based on migrating memory when
934 it has references to the node the task is running on.
936 This system will be inactive on UMA systems.
938 config NUMA_BALANCING_DEFAULT_ENABLED
939 bool "Automatically enable NUMA aware memory/task placement"
941 depends on NUMA_BALANCING
943 If set, automatic NUMA balancing will be enabled if running on a NUMA
947 bool "Control Group support"
950 This option adds support for grouping sets of processes together, for
951 use with process control subsystems such as Cpusets, CFS, memory
952 controls or device isolation.
954 - Documentation/scheduler/sched-design-CFS.txt (CFS)
955 - Documentation/cgroups/ (features for grouping, isolation
956 and resource control)
966 bool "Memory controller"
970 Provides control over the memory footprint of tasks in a cgroup.
973 bool "Swap controller"
974 depends on MEMCG && SWAP
976 Provides control over the swap space consumed by tasks in a cgroup.
978 config MEMCG_SWAP_ENABLED
979 bool "Swap controller enabled by default"
980 depends on MEMCG_SWAP
983 Memory Resource Controller Swap Extension comes with its price in
984 a bigger memory consumption. General purpose distribution kernels
985 which want to enable the feature but keep it disabled by default
986 and let the user enable it by swapaccount=1 boot command line
987 parameter should have this option unselected.
988 For those who want to have the feature enabled by default should
989 select this option (if, for some reason, they need to disable it
990 then swapaccount=0 does the trick).
997 Generic block IO controller cgroup interface. This is the common
998 cgroup interface which should be used by various IO controlling
1001 Currently, CFQ IO scheduler uses it to recognize task groups and
1002 control disk bandwidth allocation (proportional time slice allocation)
1003 to such task groups. It is also used by bio throttling logic in
1004 block layer to implement upper limit in IO rates on a device.
1006 This option only enables generic Block IO controller infrastructure.
1007 One needs to also enable actual IO controlling logic/policy. For
1008 enabling proportional weight division of disk bandwidth in CFQ, set
1009 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1010 CONFIG_BLK_DEV_THROTTLING=y.
1012 See Documentation/cgroups/blkio-controller.txt for more information.
1014 config DEBUG_BLK_CGROUP
1015 bool "IO controller debugging"
1016 depends on BLK_CGROUP
1019 Enable some debugging help. Currently it exports additional stat
1020 files in a cgroup which can be useful for debugging.
1022 config CGROUP_WRITEBACK
1024 depends on MEMCG && BLK_CGROUP
1027 menuconfig CGROUP_SCHED
1028 bool "CPU controller"
1031 This feature lets CPU scheduler recognize task groups and control CPU
1032 bandwidth allocation to such task groups. It uses cgroups to group
1036 config FAIR_GROUP_SCHED
1037 bool "Group scheduling for SCHED_OTHER"
1038 depends on CGROUP_SCHED
1039 default CGROUP_SCHED
1041 config CFS_BANDWIDTH
1042 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1043 depends on FAIR_GROUP_SCHED
1046 This option allows users to define CPU bandwidth rates (limits) for
1047 tasks running within the fair group scheduler. Groups with no limit
1048 set are considered to be unconstrained and will run with no
1050 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1052 config RT_GROUP_SCHED
1053 bool "Group scheduling for SCHED_RR/FIFO"
1054 depends on CGROUP_SCHED
1057 This feature lets you explicitly allocate real CPU bandwidth
1058 to task groups. If enabled, it will also make it impossible to
1059 schedule realtime tasks for non-root users until you allocate
1060 realtime bandwidth for them.
1061 See Documentation/scheduler/sched-rt-group.txt for more information.
1066 bool "PIDs controller"
1068 Provides enforcement of process number limits in the scope of a
1069 cgroup. Any attempt to fork more processes than is allowed in the
1070 cgroup will fail. PIDs are fundamentally a global resource because it
1071 is fairly trivial to reach PID exhaustion before you reach even a
1072 conservative kmemcg limit. As a result, it is possible to grind a
1073 system to halt without being limited by other cgroup policies. The
1074 PIDs controller is designed to stop this from happening.
1076 It should be noted that organisational operations (such as attaching
1077 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1078 since the PIDs limit only affects a process's ability to fork, not to
1081 config CGROUP_FREEZER
1082 bool "Freezer controller"
1084 Provides a way to freeze and unfreeze all tasks in a
1087 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1088 controller includes important in-kernel memory consumers per default.
1090 If you're using cgroup2, say N.
1092 config CGROUP_HUGETLB
1093 bool "HugeTLB controller"
1094 depends on HUGETLB_PAGE
1098 Provides a cgroup controller for HugeTLB pages.
1099 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1100 The limit is enforced during page fault. Since HugeTLB doesn't
1101 support page reclaim, enforcing the limit at page fault time implies
1102 that, the application will get SIGBUS signal if it tries to access
1103 HugeTLB pages beyond its limit. This requires the application to know
1104 beforehand how much HugeTLB pages it would require for its use. The
1105 control group is tracked in the third page lru pointer. This means
1106 that we cannot use the controller with huge page less than 3 pages.
1109 bool "Cpuset controller"
1111 This option will let you create and manage CPUSETs which
1112 allow dynamically partitioning a system into sets of CPUs and
1113 Memory Nodes and assigning tasks to run only within those sets.
1114 This is primarily useful on large SMP or NUMA systems.
1118 config PROC_PID_CPUSET
1119 bool "Include legacy /proc/<pid>/cpuset file"
1123 config CGROUP_DEVICE
1124 bool "Device controller"
1126 Provides a cgroup controller implementing whitelists for
1127 devices which a process in the cgroup can mknod or open.
1129 config CGROUP_CPUACCT
1130 bool "Simple CPU accounting controller"
1132 Provides a simple controller for monitoring the
1133 total CPU consumed by the tasks in a cgroup.
1136 bool "Perf controller"
1137 depends on PERF_EVENTS
1139 This option extends the perf per-cpu mode to restrict monitoring
1140 to threads which belong to the cgroup specified and run on the
1146 bool "Example controller"
1149 This option enables a simple controller that exports
1150 debugging information about the cgroups framework.
1156 config CHECKPOINT_RESTORE
1157 bool "Checkpoint/restore support" if EXPERT
1158 select PROC_CHILDREN
1161 Enables additional kernel features in a sake of checkpoint/restore.
1162 In particular it adds auxiliary prctl codes to setup process text,
1163 data and heap segment sizes, and a few additional /proc filesystem
1166 If unsure, say N here.
1168 menuconfig NAMESPACES
1169 bool "Namespaces support" if EXPERT
1170 depends on MULTIUSER
1173 Provides the way to make tasks work with different objects using
1174 the same id. For example same IPC id may refer to different objects
1175 or same user id or pid may refer to different tasks when used in
1176 different namespaces.
1181 bool "UTS namespace"
1184 In this namespace tasks see different info provided with the
1188 bool "IPC namespace"
1189 depends on (SYSVIPC || POSIX_MQUEUE)
1192 In this namespace tasks work with IPC ids which correspond to
1193 different IPC objects in different namespaces.
1196 bool "User namespace"
1199 This allows containers, i.e. vservers, to use user namespaces
1200 to provide different user info for different servers.
1202 When user namespaces are enabled in the kernel it is
1203 recommended that the MEMCG option also be enabled and that
1204 user-space use the memory control groups to limit the amount
1205 of memory a memory unprivileged users can use.
1210 bool "PID Namespaces"
1213 Support process id namespaces. This allows having multiple
1214 processes with the same pid as long as they are in different
1215 pid namespaces. This is a building block of containers.
1218 bool "Network namespace"
1222 Allow user space to create what appear to be multiple instances
1223 of the network stack.
1227 config SCHED_AUTOGROUP
1228 bool "Automatic process group scheduling"
1231 select FAIR_GROUP_SCHED
1233 This option optimizes the scheduler for common desktop workloads by
1234 automatically creating and populating task groups. This separation
1235 of workloads isolates aggressive CPU burners (like build jobs) from
1236 desktop applications. Task group autogeneration is currently based
1239 config SYSFS_DEPRECATED
1240 bool "Enable deprecated sysfs features to support old userspace tools"
1244 This option adds code that switches the layout of the "block" class
1245 devices, to not show up in /sys/class/block/, but only in
1248 This switch is only active when the sysfs.deprecated=1 boot option is
1249 passed or the SYSFS_DEPRECATED_V2 option is set.
1251 This option allows new kernels to run on old distributions and tools,
1252 which might get confused by /sys/class/block/. Since 2007/2008 all
1253 major distributions and tools handle this just fine.
1255 Recent distributions and userspace tools after 2009/2010 depend on
1256 the existence of /sys/class/block/, and will not work with this
1259 Only if you are using a new kernel on an old distribution, you might
1262 config SYSFS_DEPRECATED_V2
1263 bool "Enable deprecated sysfs features by default"
1266 depends on SYSFS_DEPRECATED
1268 Enable deprecated sysfs by default.
1270 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1273 Only if you are using a new kernel on an old distribution, you might
1274 need to say Y here. Even then, odds are you would not need it
1275 enabled, you can always pass the boot option if absolutely necessary.
1278 bool "Kernel->user space relay support (formerly relayfs)"
1280 This option enables support for relay interface support in
1281 certain file systems (such as debugfs).
1282 It is designed to provide an efficient mechanism for tools and
1283 facilities to relay large amounts of data from kernel space to
1288 config BLK_DEV_INITRD
1289 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1290 depends on BROKEN || !FRV
1292 The initial RAM filesystem is a ramfs which is loaded by the
1293 boot loader (loadlin or lilo) and that is mounted as root
1294 before the normal boot procedure. It is typically used to
1295 load modules needed to mount the "real" root file system,
1296 etc. See <file:Documentation/initrd.txt> for details.
1298 If RAM disk support (BLK_DEV_RAM) is also included, this
1299 also enables initial RAM disk (initrd) support and adds
1300 15 Kbytes (more on some other architectures) to the kernel size.
1306 source "usr/Kconfig"
1311 prompt "Compiler optimization level"
1312 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1314 config CC_OPTIMIZE_FOR_PERFORMANCE
1315 bool "Optimize for performance"
1317 This is the default optimization level for the kernel, building
1318 with the "-O2" compiler flag for best performance and most
1319 helpful compile-time warnings.
1321 config CC_OPTIMIZE_FOR_SIZE
1322 bool "Optimize for size"
1324 Enabling this option will pass "-Os" instead of "-O2" to
1325 your compiler resulting in a smaller kernel.
1340 config SYSCTL_EXCEPTION_TRACE
1343 Enable support for /proc/sys/debug/exception-trace.
1345 config SYSCTL_ARCH_UNALIGN_NO_WARN
1348 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1349 Allows arch to define/use @no_unaligned_warning to possibly warn
1350 about unaligned access emulation going on under the hood.
1352 config SYSCTL_ARCH_UNALIGN_ALLOW
1355 Enable support for /proc/sys/kernel/unaligned-trap
1356 Allows arches to define/use @unaligned_enabled to runtime toggle
1357 the unaligned access emulation.
1358 see arch/parisc/kernel/unaligned.c for reference
1360 config HAVE_PCSPKR_PLATFORM
1363 # interpreter that classic socket filters depend on
1368 bool "Configure standard kernel features (expert users)"
1369 # Unhide debug options, to make the on-by-default options visible
1372 This option allows certain base kernel options and settings
1373 to be disabled or tweaked. This is for specialized
1374 environments which can tolerate a "non-standard" kernel.
1375 Only use this if you really know what you are doing.
1378 bool "Enable 16-bit UID system calls" if EXPERT
1379 depends on HAVE_UID16 && MULTIUSER
1382 This enables the legacy 16-bit UID syscall wrappers.
1385 bool "Multiple users, groups and capabilities support" if EXPERT
1388 This option enables support for non-root users, groups and
1391 If you say N here, all processes will run with UID 0, GID 0, and all
1392 possible capabilities. Saying N here also compiles out support for
1393 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1396 If unsure, say Y here.
1398 config SGETMASK_SYSCALL
1399 bool "sgetmask/ssetmask syscalls support" if EXPERT
1400 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1402 sys_sgetmask and sys_ssetmask are obsolete system calls
1403 no longer supported in libc but still enabled by default in some
1406 If unsure, leave the default option here.
1408 config SYSFS_SYSCALL
1409 bool "Sysfs syscall support" if EXPERT
1412 sys_sysfs is an obsolete system call no longer supported in libc.
1413 Note that disabling this option is more secure but might break
1414 compatibility with some systems.
1416 If unsure say Y here.
1418 config SYSCTL_SYSCALL
1419 bool "Sysctl syscall support" if EXPERT
1420 depends on PROC_SYSCTL
1424 sys_sysctl uses binary paths that have been found challenging
1425 to properly maintain and use. The interface in /proc/sys
1426 using paths with ascii names is now the primary path to this
1429 Almost nothing using the binary sysctl interface so if you are
1430 trying to save some space it is probably safe to disable this,
1431 making your kernel marginally smaller.
1433 If unsure say N here.
1436 bool "Load all symbols for debugging/ksymoops" if EXPERT
1439 Say Y here to let the kernel print out symbolic crash information and
1440 symbolic stack backtraces. This increases the size of the kernel
1441 somewhat, as all symbols have to be loaded into the kernel image.
1444 bool "Include all symbols in kallsyms"
1445 depends on DEBUG_KERNEL && KALLSYMS
1447 Normally kallsyms only contains the symbols of functions for nicer
1448 OOPS messages and backtraces (i.e., symbols from the text and inittext
1449 sections). This is sufficient for most cases. And only in very rare
1450 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1451 names of variables from the data sections, etc).
1453 This option makes sure that all symbols are loaded into the kernel
1454 image (i.e., symbols from all sections) in cost of increased kernel
1455 size (depending on the kernel configuration, it may be 300KiB or
1456 something like this).
1458 Say N unless you really need all symbols.
1460 config KALLSYMS_ABSOLUTE_PERCPU
1463 default X86_64 && SMP
1465 config KALLSYMS_BASE_RELATIVE
1468 default !IA64 && !(TILE && 64BIT)
1470 Instead of emitting them as absolute values in the native word size,
1471 emit the symbol references in the kallsyms table as 32-bit entries,
1472 each containing a relative value in the range [base, base + U32_MAX]
1473 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1474 an absolute value in the range [0, S32_MAX] or a relative value in the
1475 range [base, base + S32_MAX], where base is the lowest relative symbol
1476 address encountered in the image.
1478 On 64-bit builds, this reduces the size of the address table by 50%,
1479 but more importantly, it results in entries whose values are build
1480 time constants, and no relocation pass is required at runtime to fix
1481 up the entries based on the runtime load address of the kernel.
1485 bool "Enable support for printk" if EXPERT
1488 This option enables normal printk support. Removing it
1489 eliminates most of the message strings from the kernel image
1490 and makes the kernel more or less silent. As this makes it
1491 very difficult to diagnose system problems, saying N here is
1492 strongly discouraged.
1500 bool "BUG() support" if EXPERT
1503 Disabling this option eliminates support for BUG and WARN, reducing
1504 the size of your kernel image and potentially quietly ignoring
1505 numerous fatal conditions. You should only consider disabling this
1506 option for embedded systems with no facilities for reporting errors.
1512 bool "Enable ELF core dumps" if EXPERT
1514 Enable support for generating core dumps. Disabling saves about 4k.
1517 config PCSPKR_PLATFORM
1518 bool "Enable PC-Speaker support" if EXPERT
1519 depends on HAVE_PCSPKR_PLATFORM
1523 This option allows to disable the internal PC-Speaker
1524 support, saving some memory.
1528 bool "Enable full-sized data structures for core" if EXPERT
1530 Disabling this option reduces the size of miscellaneous core
1531 kernel data structures. This saves memory on small machines,
1532 but may reduce performance.
1535 bool "Enable futex support" if EXPERT
1539 Disabling this option will cause the kernel to be built without
1540 support for "fast userspace mutexes". The resulting kernel may not
1541 run glibc-based applications correctly.
1543 config HAVE_FUTEX_CMPXCHG
1547 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1548 is implemented and always working. This removes a couple of runtime
1552 bool "Enable eventpoll support" if EXPERT
1556 Disabling this option will cause the kernel to be built without
1557 support for epoll family of system calls.
1560 bool "Enable signalfd() system call" if EXPERT
1564 Enable the signalfd() system call that allows to receive signals
1565 on a file descriptor.
1570 bool "Enable timerfd() system call" if EXPERT
1574 Enable the timerfd() system call that allows to receive timer
1575 events on a file descriptor.
1580 bool "Enable eventfd() system call" if EXPERT
1584 Enable the eventfd() system call that allows to receive both
1585 kernel notification (ie. KAIO) or userspace notifications.
1589 # syscall, maps, verifier
1591 bool "Enable bpf() system call"
1596 Enable the bpf() system call that allows to manipulate eBPF
1597 programs and maps via file descriptors.
1600 bool "Use full shmem filesystem" if EXPERT
1604 The shmem is an internal filesystem used to manage shared memory.
1605 It is backed by swap and manages resource limits. It is also exported
1606 to userspace as tmpfs if TMPFS is enabled. Disabling this
1607 option replaces shmem and tmpfs with the much simpler ramfs code,
1608 which may be appropriate on small systems without swap.
1611 bool "Enable AIO support" if EXPERT
1614 This option enables POSIX asynchronous I/O which may by used
1615 by some high performance threaded applications. Disabling
1616 this option saves about 7k.
1618 config ADVISE_SYSCALLS
1619 bool "Enable madvise/fadvise syscalls" if EXPERT
1622 This option enables the madvise and fadvise syscalls, used by
1623 applications to advise the kernel about their future memory or file
1624 usage, improving performance. If building an embedded system where no
1625 applications use these syscalls, you can disable this option to save
1629 bool "Enable userfaultfd() system call"
1633 Enable the userfaultfd() system call that allows to intercept and
1634 handle page faults in userland.
1638 bool "Enable PCI quirk workarounds" if EXPERT
1641 This enables workarounds for various PCI chipset
1642 bugs/quirks. Disable this only if your target machine is
1643 unaffected by PCI quirks.
1646 bool "Enable membarrier() system call" if EXPERT
1649 Enable the membarrier() system call that allows issuing memory
1650 barriers across all running threads, which can be used to distribute
1651 the cost of user-space memory barriers asymmetrically by transforming
1652 pairs of memory barriers into pairs consisting of membarrier() and a
1658 bool "Embedded system"
1659 option allnoconfig_y
1662 This option should be enabled if compiling the kernel for
1663 an embedded system so certain expert options are available
1666 config HAVE_PERF_EVENTS
1669 See tools/perf/design.txt for details.
1671 config PERF_USE_VMALLOC
1674 See tools/perf/design.txt for details
1676 menu "Kernel Performance Events And Counters"
1679 bool "Kernel performance events and counters"
1680 default y if PROFILING
1681 depends on HAVE_PERF_EVENTS
1686 Enable kernel support for various performance events provided
1687 by software and hardware.
1689 Software events are supported either built-in or via the
1690 use of generic tracepoints.
1692 Most modern CPUs support performance events via performance
1693 counter registers. These registers count the number of certain
1694 types of hw events: such as instructions executed, cachemisses
1695 suffered, or branches mis-predicted - without slowing down the
1696 kernel or applications. These registers can also trigger interrupts
1697 when a threshold number of events have passed - and can thus be
1698 used to profile the code that runs on that CPU.
1700 The Linux Performance Event subsystem provides an abstraction of
1701 these software and hardware event capabilities, available via a
1702 system call and used by the "perf" utility in tools/perf/. It
1703 provides per task and per CPU counters, and it provides event
1704 capabilities on top of those.
1708 config DEBUG_PERF_USE_VMALLOC
1710 bool "Debug: use vmalloc to back perf mmap() buffers"
1711 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1712 select PERF_USE_VMALLOC
1714 Use vmalloc memory to back perf mmap() buffers.
1716 Mostly useful for debugging the vmalloc code on platforms
1717 that don't require it.
1723 config VM_EVENT_COUNTERS
1725 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1727 VM event counters are needed for event counts to be shown.
1728 This option allows the disabling of the VM event counters
1729 on EXPERT systems. /proc/vmstat will only show page counts
1730 if VM event counters are disabled.
1734 bool "Enable SLUB debugging support" if EXPERT
1735 depends on SLUB && SYSFS
1737 SLUB has extensive debug support features. Disabling these can
1738 result in significant savings in code size. This also disables
1739 SLUB sysfs support. /sys/slab will not exist and there will be
1740 no support for cache validation etc.
1743 bool "Disable heap randomization"
1746 Randomizing heap placement makes heap exploits harder, but it
1747 also breaks ancient binaries (including anything libc5 based).
1748 This option changes the bootup default to heap randomization
1749 disabled, and can be overridden at runtime by setting
1750 /proc/sys/kernel/randomize_va_space to 2.
1752 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1755 prompt "Choose SLAB allocator"
1758 This option allows to select a slab allocator.
1763 The regular slab allocator that is established and known to work
1764 well in all environments. It organizes cache hot objects in
1765 per cpu and per node queues.
1768 bool "SLUB (Unqueued Allocator)"
1770 SLUB is a slab allocator that minimizes cache line usage
1771 instead of managing queues of cached objects (SLAB approach).
1772 Per cpu caching is realized using slabs of objects instead
1773 of queues of objects. SLUB can use memory efficiently
1774 and has enhanced diagnostics. SLUB is the default choice for
1779 bool "SLOB (Simple Allocator)"
1781 SLOB replaces the stock allocator with a drastically simpler
1782 allocator. SLOB is generally more space efficient but
1783 does not perform as well on large systems.
1787 config SLAB_FREELIST_RANDOM
1790 bool "SLAB freelist randomization"
1792 Randomizes the freelist order used on creating new SLABs. This
1793 security feature reduces the predictability of the kernel slab
1794 allocator against heap overflows.
1796 config SLUB_CPU_PARTIAL
1798 depends on SLUB && SMP
1799 bool "SLUB per cpu partial cache"
1801 Per cpu partial caches accellerate objects allocation and freeing
1802 that is local to a processor at the price of more indeterminism
1803 in the latency of the free. On overflow these caches will be cleared
1804 which requires the taking of locks that may cause latency spikes.
1805 Typically one would choose no for a realtime system.
1807 config MMAP_ALLOW_UNINITIALIZED
1808 bool "Allow mmapped anonymous memory to be uninitialized"
1809 depends on EXPERT && !MMU
1812 Normally, and according to the Linux spec, anonymous memory obtained
1813 from mmap() has it's contents cleared before it is passed to
1814 userspace. Enabling this config option allows you to request that
1815 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1816 providing a huge performance boost. If this option is not enabled,
1817 then the flag will be ignored.
1819 This is taken advantage of by uClibc's malloc(), and also by
1820 ELF-FDPIC binfmt's brk and stack allocator.
1822 Because of the obvious security issues, this option should only be
1823 enabled on embedded devices where you control what is run in
1824 userspace. Since that isn't generally a problem on no-MMU systems,
1825 it is normally safe to say Y here.
1827 See Documentation/nommu-mmap.txt for more information.
1829 config SYSTEM_DATA_VERIFICATION
1831 select SYSTEM_TRUSTED_KEYRING
1835 select ASYMMETRIC_KEY_TYPE
1836 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1839 select X509_CERTIFICATE_PARSER
1840 select PKCS7_MESSAGE_PARSER
1842 Provide PKCS#7 message verification using the contents of the system
1843 trusted keyring to provide public keys. This then can be used for
1844 module verification, kexec image verification and firmware blob
1848 bool "Profiling support"
1850 Say Y here to enable the extended profiling support mechanisms used
1851 by profilers such as OProfile.
1854 # Place an empty function call at each tracepoint site. Can be
1855 # dynamically changed for a probe function.
1860 source "arch/Kconfig"
1862 endmenu # General setup
1864 config HAVE_GENERIC_DMA_COHERENT
1871 depends on SLAB || SLUB_DEBUG
1879 default 0 if BASE_FULL
1880 default 1 if !BASE_FULL
1883 bool "Enable loadable module support"
1886 Kernel modules are small pieces of compiled code which can
1887 be inserted in the running kernel, rather than being
1888 permanently built into the kernel. You use the "modprobe"
1889 tool to add (and sometimes remove) them. If you say Y here,
1890 many parts of the kernel can be built as modules (by
1891 answering M instead of Y where indicated): this is most
1892 useful for infrequently used options which are not required
1893 for booting. For more information, see the man pages for
1894 modprobe, lsmod, modinfo, insmod and rmmod.
1896 If you say Y here, you will need to run "make
1897 modules_install" to put the modules under /lib/modules/
1898 where modprobe can find them (you may need to be root to do
1905 config MODULE_FORCE_LOAD
1906 bool "Forced module loading"
1909 Allow loading of modules without version information (ie. modprobe
1910 --force). Forced module loading sets the 'F' (forced) taint flag and
1911 is usually a really bad idea.
1913 config MODULE_UNLOAD
1914 bool "Module unloading"
1916 Without this option you will not be able to unload any
1917 modules (note that some modules may not be unloadable
1918 anyway), which makes your kernel smaller, faster
1919 and simpler. If unsure, say Y.
1921 config MODULE_FORCE_UNLOAD
1922 bool "Forced module unloading"
1923 depends on MODULE_UNLOAD
1925 This option allows you to force a module to unload, even if the
1926 kernel believes it is unsafe: the kernel will remove the module
1927 without waiting for anyone to stop using it (using the -f option to
1928 rmmod). This is mainly for kernel developers and desperate users.
1932 bool "Module versioning support"
1934 Usually, you have to use modules compiled with your kernel.
1935 Saying Y here makes it sometimes possible to use modules
1936 compiled for different kernels, by adding enough information
1937 to the modules to (hopefully) spot any changes which would
1938 make them incompatible with the kernel you are running. If
1941 config MODULE_SRCVERSION_ALL
1942 bool "Source checksum for all modules"
1944 Modules which contain a MODULE_VERSION get an extra "srcversion"
1945 field inserted into their modinfo section, which contains a
1946 sum of the source files which made it. This helps maintainers
1947 see exactly which source was used to build a module (since
1948 others sometimes change the module source without updating
1949 the version). With this option, such a "srcversion" field
1950 will be created for all modules. If unsure, say N.
1953 bool "Module signature verification"
1955 select SYSTEM_DATA_VERIFICATION
1957 Check modules for valid signatures upon load: the signature
1958 is simply appended to the module. For more information see
1959 Documentation/module-signing.txt.
1961 Note that this option adds the OpenSSL development packages as a
1962 kernel build dependency so that the signing tool can use its crypto
1965 !!!WARNING!!! If you enable this option, you MUST make sure that the
1966 module DOES NOT get stripped after being signed. This includes the
1967 debuginfo strip done by some packagers (such as rpmbuild) and
1968 inclusion into an initramfs that wants the module size reduced.
1970 config MODULE_SIG_FORCE
1971 bool "Require modules to be validly signed"
1972 depends on MODULE_SIG
1974 Reject unsigned modules or signed modules for which we don't have a
1975 key. Without this, such modules will simply taint the kernel.
1977 config MODULE_SIG_ALL
1978 bool "Automatically sign all modules"
1980 depends on MODULE_SIG
1982 Sign all modules during make modules_install. Without this option,
1983 modules must be signed manually, using the scripts/sign-file tool.
1985 comment "Do not forget to sign required modules with scripts/sign-file"
1986 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1989 prompt "Which hash algorithm should modules be signed with?"
1990 depends on MODULE_SIG
1992 This determines which sort of hashing algorithm will be used during
1993 signature generation. This algorithm _must_ be built into the kernel
1994 directly so that signature verification can take place. It is not
1995 possible to load a signed module containing the algorithm to check
1996 the signature on that module.
1998 config MODULE_SIG_SHA1
1999 bool "Sign modules with SHA-1"
2002 config MODULE_SIG_SHA224
2003 bool "Sign modules with SHA-224"
2004 select CRYPTO_SHA256
2006 config MODULE_SIG_SHA256
2007 bool "Sign modules with SHA-256"
2008 select CRYPTO_SHA256
2010 config MODULE_SIG_SHA384
2011 bool "Sign modules with SHA-384"
2012 select CRYPTO_SHA512
2014 config MODULE_SIG_SHA512
2015 bool "Sign modules with SHA-512"
2016 select CRYPTO_SHA512
2020 config MODULE_SIG_HASH
2022 depends on MODULE_SIG
2023 default "sha1" if MODULE_SIG_SHA1
2024 default "sha224" if MODULE_SIG_SHA224
2025 default "sha256" if MODULE_SIG_SHA256
2026 default "sha384" if MODULE_SIG_SHA384
2027 default "sha512" if MODULE_SIG_SHA512
2029 config MODULE_COMPRESS
2030 bool "Compress modules on installation"
2034 Compresses kernel modules when 'make modules_install' is run; gzip or
2035 xz depending on "Compression algorithm" below.
2037 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2039 Out-of-tree kernel modules installed using Kbuild will also be
2040 compressed upon installation.
2042 Note: for modules inside an initrd or initramfs, it's more efficient
2043 to compress the whole initrd or initramfs instead.
2045 Note: This is fully compatible with signed modules.
2050 prompt "Compression algorithm"
2051 depends on MODULE_COMPRESS
2052 default MODULE_COMPRESS_GZIP
2054 This determines which sort of compression will be used during
2055 'make modules_install'.
2057 GZIP (default) and XZ are supported.
2059 config MODULE_COMPRESS_GZIP
2062 config MODULE_COMPRESS_XZ
2067 config TRIM_UNUSED_KSYMS
2068 bool "Trim unused exported kernel symbols"
2069 depends on MODULES && !UNUSED_SYMBOLS
2071 The kernel and some modules make many symbols available for
2072 other modules to use via EXPORT_SYMBOL() and variants. Depending
2073 on the set of modules being selected in your kernel configuration,
2074 many of those exported symbols might never be used.
2076 This option allows for unused exported symbols to be dropped from
2077 the build. In turn, this provides the compiler more opportunities
2078 (especially when using LTO) for optimizing the code and reducing
2079 binary size. This might have some security advantages as well.
2085 config MODULES_TREE_LOOKUP
2087 depends on PERF_EVENTS || TRACING
2089 config INIT_ALL_POSSIBLE
2092 Back when each arch used to define their own cpu_online_mask and
2093 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2094 with all 1s, and others with all 0s. When they were centralised,
2095 it was better to provide this option than to break all the archs
2096 and have several arch maintainers pursuing me down dark alleys.
2098 source "block/Kconfig"
2100 config PREEMPT_NOTIFIERS
2107 # Can be selected by architectures with broken toolchains
2108 # that get confused by correct const<->read_only section
2110 config BROKEN_RODATA
2116 Build a simple ASN.1 grammar compiler that produces a bytecode output
2117 that can be interpreted by the ASN.1 stream decoder and used to
2118 inform it as to what tags are to be expected in a stream and what
2119 functions to call on what tags.
2121 source "kernel/Kconfig.locks"
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