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
29 config THREAD_INFO_IN_TASK
32 Select this to move thread_info off the stack into task_struct. To
33 make this work, an arch will need to remove all thread_info fields
34 except flags and fix any runtime bugs.
36 One subtle change that will be needed is to use try_get_task_stack()
37 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
46 depends on BROKEN || !SMP
49 config INIT_ENV_ARG_LIMIT
54 Maximum of each of the number of arguments and environment
55 variables passed to init from the kernel command line.
59 string "Cross-compiler tool prefix"
61 Same as running 'make CROSS_COMPILE=prefix-' but stored for
62 default make runs in this kernel build directory. You don't
63 need to set this unless you want the configured kernel build
64 directory to select the cross-compiler automatically.
67 bool "Compile also drivers which will not load"
70 Some drivers can be compiled on a different platform than they are
71 intended to be run on. Despite they cannot be loaded there (or even
72 when they load they cannot be used due to missing HW support),
73 developers still, opposing to distributors, might want to build such
74 drivers to compile-test them.
76 If you are a developer and want to build everything available, say Y
77 here. If you are a user/distributor, say N here to exclude useless
78 drivers to be distributed.
81 string "Local version - append to kernel release"
83 Append an extra string to the end of your kernel version.
84 This will show up when you type uname, for example.
85 The string you set here will be appended after the contents of
86 any files with a filename matching localversion* in your
87 object and source tree, in that order. Your total string can
88 be a maximum of 64 characters.
90 config LOCALVERSION_AUTO
91 bool "Automatically append version information to the version string"
93 depends on !COMPILE_TEST
95 This will try to automatically determine if the current tree is a
96 release tree by looking for git tags that belong to the current
99 A string of the format -gxxxxxxxx will be added to the localversion
100 if a git-based tree is found. The string generated by this will be
101 appended after any matching localversion* files, and after the value
102 set in CONFIG_LOCALVERSION.
104 (The actual string used here is the first eight characters produced
105 by running the command:
107 $ git rev-parse --verify HEAD
109 which is done within the script "scripts/setlocalversion".)
111 config HAVE_KERNEL_GZIP
114 config HAVE_KERNEL_BZIP2
117 config HAVE_KERNEL_LZMA
120 config HAVE_KERNEL_XZ
123 config HAVE_KERNEL_LZO
126 config HAVE_KERNEL_LZ4
130 prompt "Kernel compression mode"
132 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
134 The linux kernel is a kind of self-extracting executable.
135 Several compression algorithms are available, which differ
136 in efficiency, compression and decompression speed.
137 Compression speed is only relevant when building a kernel.
138 Decompression speed is relevant at each boot.
140 If you have any problems with bzip2 or lzma compressed
141 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
142 version of this functionality (bzip2 only), for 2.4, was
143 supplied by Christian Ludwig)
145 High compression options are mostly useful for users, who
146 are low on disk space (embedded systems), but for whom ram
149 If in doubt, select 'gzip'
153 depends on HAVE_KERNEL_GZIP
155 The old and tried gzip compression. It provides a good balance
156 between compression ratio and decompression speed.
160 depends on HAVE_KERNEL_BZIP2
162 Its compression ratio and speed is intermediate.
163 Decompression speed is slowest among the choices. The kernel
164 size is about 10% smaller with bzip2, in comparison to gzip.
165 Bzip2 uses a large amount of memory. For modern kernels you
166 will need at least 8MB RAM or more for booting.
170 depends on HAVE_KERNEL_LZMA
172 This compression algorithm's ratio is best. Decompression speed
173 is between gzip and bzip2. Compression is slowest.
174 The kernel size is about 33% smaller with LZMA in comparison to gzip.
178 depends on HAVE_KERNEL_XZ
180 XZ uses the LZMA2 algorithm and instruction set specific
181 BCJ filters which can improve compression ratio of executable
182 code. The size of the kernel is about 30% smaller with XZ in
183 comparison to gzip. On architectures for which there is a BCJ
184 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
185 will create a few percent smaller kernel than plain LZMA.
187 The speed is about the same as with LZMA: The decompression
188 speed of XZ is better than that of bzip2 but worse than gzip
189 and LZO. Compression is slow.
193 depends on HAVE_KERNEL_LZO
195 Its compression ratio is the poorest among the choices. The kernel
196 size is about 10% bigger than gzip; however its speed
197 (both compression and decompression) is the fastest.
201 depends on HAVE_KERNEL_LZ4
203 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
204 A preliminary version of LZ4 de/compression tool is available at
205 <https://code.google.com/p/lz4/>.
207 Its compression ratio is worse than LZO. The size of the kernel
208 is about 8% bigger than LZO. But the decompression speed is
213 config DEFAULT_HOSTNAME
214 string "Default hostname"
217 This option determines the default system hostname before userspace
218 calls sethostname(2). The kernel traditionally uses "(none)" here,
219 but you may wish to use a different default here to make a minimal
220 system more usable with less configuration.
223 bool "Support for paging of anonymous memory (swap)"
224 depends on MMU && BLOCK
227 This option allows you to choose whether you want to have support
228 for so called swap devices or swap files in your kernel that are
229 used to provide more virtual memory than the actual RAM present
230 in your computer. If unsure say Y.
235 Inter Process Communication is a suite of library functions and
236 system calls which let processes (running programs) synchronize and
237 exchange information. It is generally considered to be a good thing,
238 and some programs won't run unless you say Y here. In particular, if
239 you want to run the DOS emulator dosemu under Linux (read the
240 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
241 you'll need to say Y here.
243 You can find documentation about IPC with "info ipc" and also in
244 section 6.4 of the Linux Programmer's Guide, available from
245 <http://www.tldp.org/guides.html>.
247 config SYSVIPC_SYSCTL
254 bool "POSIX Message Queues"
257 POSIX variant of message queues is a part of IPC. In POSIX message
258 queues every message has a priority which decides about succession
259 of receiving it by a process. If you want to compile and run
260 programs written e.g. for Solaris with use of its POSIX message
261 queues (functions mq_*) say Y here.
263 POSIX message queues are visible as a filesystem called 'mqueue'
264 and can be mounted somewhere if you want to do filesystem
265 operations on message queues.
269 config POSIX_MQUEUE_SYSCTL
271 depends on POSIX_MQUEUE
275 config CROSS_MEMORY_ATTACH
276 bool "Enable process_vm_readv/writev syscalls"
280 Enabling this option adds the system calls process_vm_readv and
281 process_vm_writev which allow a process with the correct privileges
282 to directly read from or write to another process' address space.
283 See the man page for more details.
286 bool "open by fhandle syscalls" if EXPERT
290 If you say Y here, a user level program will be able to map
291 file names to handle and then later use the handle for
292 different file system operations. This is useful in implementing
293 userspace file servers, which now track files using handles instead
294 of names. The handle would remain the same even if file names
295 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
299 bool "uselib syscall"
300 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
302 This option enables the uselib syscall, a system call used in the
303 dynamic linker from libc5 and earlier. glibc does not use this
304 system call. If you intend to run programs built on libc5 or
305 earlier, you may need to enable this syscall. Current systems
306 running glibc can safely disable this.
309 bool "Auditing support"
312 Enable auditing infrastructure that can be used with another
313 kernel subsystem, such as SELinux (which requires this for
314 logging of avc messages output). System call auditing is included
315 on architectures which support it.
317 config HAVE_ARCH_AUDITSYSCALL
322 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
326 depends on AUDITSYSCALL
331 depends on AUDITSYSCALL
334 source "kernel/irq/Kconfig"
335 source "kernel/time/Kconfig"
337 menu "CPU/Task time and stats accounting"
339 config VIRT_CPU_ACCOUNTING
343 prompt "Cputime accounting"
344 default TICK_CPU_ACCOUNTING if !PPC64
345 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
347 # Kind of a stub config for the pure tick based cputime accounting
348 config TICK_CPU_ACCOUNTING
349 bool "Simple tick based cputime accounting"
350 depends on !S390 && !NO_HZ_FULL
352 This is the basic tick based cputime accounting that maintains
353 statistics about user, system and idle time spent on per jiffies
358 config VIRT_CPU_ACCOUNTING_NATIVE
359 bool "Deterministic task and CPU time accounting"
360 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
361 select VIRT_CPU_ACCOUNTING
363 Select this option to enable more accurate task and CPU time
364 accounting. This is done by reading a CPU counter on each
365 kernel entry and exit and on transitions within the kernel
366 between system, softirq and hardirq state, so there is a
367 small performance impact. In the case of s390 or IBM POWER > 5,
368 this also enables accounting of stolen time on logically-partitioned
371 config VIRT_CPU_ACCOUNTING_GEN
372 bool "Full dynticks CPU time accounting"
373 depends on HAVE_CONTEXT_TRACKING
374 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
375 select VIRT_CPU_ACCOUNTING
376 select CONTEXT_TRACKING
378 Select this option to enable task and CPU time accounting on full
379 dynticks systems. This accounting is implemented by watching every
380 kernel-user boundaries using the context tracking subsystem.
381 The accounting is thus performed at the expense of some significant
384 For now this is only useful if you are working on the full
385 dynticks subsystem development.
391 config IRQ_TIME_ACCOUNTING
392 bool "Fine granularity task level IRQ time accounting"
393 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
395 Select this option to enable fine granularity task irq time
396 accounting. This is done by reading a timestamp on each
397 transitions between softirq and hardirq state, so there can be a
398 small performance impact.
400 If in doubt, say N here.
402 config BSD_PROCESS_ACCT
403 bool "BSD Process Accounting"
406 If you say Y here, a user level program will be able to instruct the
407 kernel (via a special system call) to write process accounting
408 information to a file: whenever a process exits, information about
409 that process will be appended to the file by the kernel. The
410 information includes things such as creation time, owning user,
411 command name, memory usage, controlling terminal etc. (the complete
412 list is in the struct acct in <file:include/linux/acct.h>). It is
413 up to the user level program to do useful things with this
414 information. This is generally a good idea, so say Y.
416 config BSD_PROCESS_ACCT_V3
417 bool "BSD Process Accounting version 3 file format"
418 depends on BSD_PROCESS_ACCT
421 If you say Y here, the process accounting information is written
422 in a new file format that also logs the process IDs of each
423 process and it's parent. Note that this file format is incompatible
424 with previous v0/v1/v2 file formats, so you will need updated tools
425 for processing it. A preliminary version of these tools is available
426 at <http://www.gnu.org/software/acct/>.
429 bool "Export task/process statistics through netlink"
434 Export selected statistics for tasks/processes through the
435 generic netlink interface. Unlike BSD process accounting, the
436 statistics are available during the lifetime of tasks/processes as
437 responses to commands. Like BSD accounting, they are sent to user
442 config TASK_DELAY_ACCT
443 bool "Enable per-task delay accounting"
447 Collect information on time spent by a task waiting for system
448 resources like cpu, synchronous block I/O completion and swapping
449 in pages. Such statistics can help in setting a task's priorities
450 relative to other tasks for cpu, io, rss limits etc.
455 bool "Enable extended accounting over taskstats"
458 Collect extended task accounting data and send the data
459 to userland for processing over the taskstats interface.
463 config TASK_IO_ACCOUNTING
464 bool "Enable per-task storage I/O accounting"
465 depends on TASK_XACCT
467 Collect information on the number of bytes of storage I/O which this
472 endmenu # "CPU/Task time and stats accounting"
478 default y if !PREEMPT && SMP
480 This option selects the RCU implementation that is
481 designed for very large SMP system with hundreds or
482 thousands of CPUs. It also scales down nicely to
489 This option selects the RCU implementation that is
490 designed for very large SMP systems with hundreds or
491 thousands of CPUs, but for which real-time response
492 is also required. It also scales down nicely to
495 Select this option if you are unsure.
499 default y if !PREEMPT && !SMP
501 This option selects the RCU implementation that is
502 designed for UP systems from which real-time response
503 is not required. This option greatly reduces the
504 memory footprint of RCU.
507 bool "Make expert-level adjustments to RCU configuration"
510 This option needs to be enabled if you wish to make
511 expert-level adjustments to RCU configuration. By default,
512 no such adjustments can be made, which has the often-beneficial
513 side-effect of preventing "make oldconfig" from asking you all
514 sorts of detailed questions about how you would like numerous
515 obscure RCU options to be set up.
517 Say Y if you need to make expert-level adjustments to RCU.
519 Say N if you are unsure.
524 This option selects the sleepable version of RCU. This version
525 permits arbitrary sleeping or blocking within RCU read-side critical
534 This option enables a task-based RCU implementation that uses
535 only voluntary context switch (not preemption!), idle, and
536 user-mode execution as quiescent states.
538 config RCU_STALL_COMMON
539 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
541 This option enables RCU CPU stall code that is common between
542 the TINY and TREE variants of RCU. The purpose is to allow
543 the tiny variants to disable RCU CPU stall warnings, while
544 making these warnings mandatory for the tree variants.
546 config CONTEXT_TRACKING
549 config CONTEXT_TRACKING_FORCE
550 bool "Force context tracking"
551 depends on CONTEXT_TRACKING
552 default y if !NO_HZ_FULL
554 The major pre-requirement for full dynticks to work is to
555 support the context tracking subsystem. But there are also
556 other dependencies to provide in order to make the full
559 This option stands for testing when an arch implements the
560 context tracking backend but doesn't yet fullfill all the
561 requirements to make the full dynticks feature working.
562 Without the full dynticks, there is no way to test the support
563 for context tracking and the subsystems that rely on it: RCU
564 userspace extended quiescent state and tickless cputime
565 accounting. This option copes with the absence of the full
566 dynticks subsystem by forcing the context tracking on all
569 Say Y only if you're working on the development of an
570 architecture backend for the context tracking.
572 Say N otherwise, this option brings an overhead that you
573 don't want in production.
577 int "Tree-based hierarchical RCU fanout value"
580 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
584 This option controls the fanout of hierarchical implementations
585 of RCU, allowing RCU to work efficiently on machines with
586 large numbers of CPUs. This value must be at least the fourth
587 root of NR_CPUS, which allows NR_CPUS to be insanely large.
588 The default value of RCU_FANOUT should be used for production
589 systems, but if you are stress-testing the RCU implementation
590 itself, small RCU_FANOUT values allow you to test large-system
591 code paths on small(er) systems.
593 Select a specific number if testing RCU itself.
594 Take the default if unsure.
596 config RCU_FANOUT_LEAF
597 int "Tree-based hierarchical RCU leaf-level fanout value"
600 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
603 This option controls the leaf-level fanout of hierarchical
604 implementations of RCU, and allows trading off cache misses
605 against lock contention. Systems that synchronize their
606 scheduling-clock interrupts for energy-efficiency reasons will
607 want the default because the smaller leaf-level fanout keeps
608 lock contention levels acceptably low. Very large systems
609 (hundreds or thousands of CPUs) will instead want to set this
610 value to the maximum value possible in order to reduce the
611 number of cache misses incurred during RCU's grace-period
612 initialization. These systems tend to run CPU-bound, and thus
613 are not helped by synchronized interrupts, and thus tend to
614 skew them, which reduces lock contention enough that large
615 leaf-level fanouts work well.
617 Select a specific number if testing RCU itself.
619 Select the maximum permissible value for large systems.
621 Take the default if unsure.
623 config RCU_FAST_NO_HZ
624 bool "Accelerate last non-dyntick-idle CPU's grace periods"
625 depends on NO_HZ_COMMON && SMP && RCU_EXPERT
628 This option permits CPUs to enter dynticks-idle state even if
629 they have RCU callbacks queued, and prevents RCU from waking
630 these CPUs up more than roughly once every four jiffies (by
631 default, you can adjust this using the rcutree.rcu_idle_gp_delay
632 parameter), thus improving energy efficiency. On the other
633 hand, this option increases the duration of RCU grace periods,
634 for example, slowing down synchronize_rcu().
636 Say Y if energy efficiency is critically important, and you
637 don't care about increased grace-period durations.
639 Say N if you are unsure.
641 config TREE_RCU_TRACE
642 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
645 This option provides tracing for the TREE_RCU and
646 PREEMPT_RCU implementations, permitting Makefile to
647 trivially select kernel/rcutree_trace.c.
650 bool "Enable RCU priority boosting"
651 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
654 This option boosts the priority of preempted RCU readers that
655 block the current preemptible RCU grace period for too long.
656 This option also prevents heavy loads from blocking RCU
657 callback invocation for all flavors of RCU.
659 Say Y here if you are working with real-time apps or heavy loads
660 Say N here if you are unsure.
662 config RCU_KTHREAD_PRIO
663 int "Real-time priority to use for RCU worker threads"
664 range 1 99 if RCU_BOOST
665 range 0 99 if !RCU_BOOST
666 default 1 if RCU_BOOST
667 default 0 if !RCU_BOOST
668 depends on RCU_EXPERT
670 This option specifies the SCHED_FIFO priority value that will be
671 assigned to the rcuc/n and rcub/n threads and is also the value
672 used for RCU_BOOST (if enabled). If you are working with a
673 real-time application that has one or more CPU-bound threads
674 running at a real-time priority level, you should set
675 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
676 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
677 value of 1 is appropriate in the common case, which is real-time
678 applications that do not have any CPU-bound threads.
680 Some real-time applications might not have a single real-time
681 thread that saturates a given CPU, but instead might have
682 multiple real-time threads that, taken together, fully utilize
683 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
684 a priority higher than the lowest-priority thread that is
685 conspiring to prevent the CPU from running any non-real-time
686 tasks. For example, if one thread at priority 10 and another
687 thread at priority 5 are between themselves fully consuming
688 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
689 set to priority 6 or higher.
691 Specify the real-time priority, or take the default if unsure.
693 config RCU_BOOST_DELAY
694 int "Milliseconds to delay boosting after RCU grace-period start"
699 This option specifies the time to wait after the beginning of
700 a given grace period before priority-boosting preempted RCU
701 readers blocking that grace period. Note that any RCU reader
702 blocking an expedited RCU grace period is boosted immediately.
704 Accept the default if unsure.
707 bool "Offload RCU callback processing from boot-selected CPUs"
708 depends on TREE_RCU || PREEMPT_RCU
709 depends on RCU_EXPERT || NO_HZ_FULL
712 Use this option to reduce OS jitter for aggressive HPC or
713 real-time workloads. It can also be used to offload RCU
714 callback invocation to energy-efficient CPUs in battery-powered
715 asymmetric multiprocessors.
717 This option offloads callback invocation from the set of
718 CPUs specified at boot time by the rcu_nocbs parameter.
719 For each such CPU, a kthread ("rcuox/N") will be created to
720 invoke callbacks, where the "N" is the CPU being offloaded,
721 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
722 "s" for RCU-sched. Nothing prevents this kthread from running
723 on the specified CPUs, but (1) the kthreads may be preempted
724 between each callback, and (2) affinity or cgroups can be used
725 to force the kthreads to run on whatever set of CPUs is desired.
727 Say Y here if you want to help to debug reduced OS jitter.
728 Say N here if you are unsure.
731 prompt "Build-forced no-CBs CPUs"
732 default RCU_NOCB_CPU_NONE
733 depends on RCU_NOCB_CPU
735 This option allows no-CBs CPUs (whose RCU callbacks are invoked
736 from kthreads rather than from softirq context) to be specified
737 at build time. Additional no-CBs CPUs may be specified by
738 the rcu_nocbs= boot parameter.
740 config RCU_NOCB_CPU_NONE
741 bool "No build_forced no-CBs CPUs"
743 This option does not force any of the CPUs to be no-CBs CPUs.
744 Only CPUs designated by the rcu_nocbs= boot parameter will be
745 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
746 kthreads whose names begin with "rcuo". All other CPUs will
747 invoke their own RCU callbacks in softirq context.
749 Select this option if you want to choose no-CBs CPUs at
750 boot time, for example, to allow testing of different no-CBs
751 configurations without having to rebuild the kernel each time.
753 config RCU_NOCB_CPU_ZERO
754 bool "CPU 0 is a build_forced no-CBs CPU"
756 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
757 callbacks are invoked by a per-CPU kthread whose name begins
758 with "rcuo". Additional CPUs may be designated as no-CBs
759 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
760 All other CPUs will invoke their own RCU callbacks in softirq
763 Select this if CPU 0 needs to be a no-CBs CPU for real-time
764 or energy-efficiency reasons, but the real reason it exists
765 is to ensure that randconfig testing covers mixed systems.
767 config RCU_NOCB_CPU_ALL
768 bool "All CPUs are build_forced no-CBs CPUs"
770 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
771 boot parameter will be ignored. All CPUs' RCU callbacks will
772 be executed in the context of per-CPU rcuo kthreads created for
773 this purpose. Assuming that the kthreads whose names start with
774 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
775 on the remaining CPUs, but might decrease memory locality during
776 RCU-callback invocation, thus potentially degrading throughput.
778 Select this if all CPUs need to be no-CBs CPUs for real-time
779 or energy-efficiency reasons.
783 config RCU_EXPEDITE_BOOT
787 This option enables expedited grace periods at boot time,
788 as if rcu_expedite_gp() had been invoked early in boot.
789 The corresponding rcu_unexpedite_gp() is invoked from
790 rcu_end_inkernel_boot(), which is intended to be invoked
791 at the end of the kernel-only boot sequence, just before
794 Accept the default if unsure.
796 endmenu # "RCU Subsystem"
803 tristate "Kernel .config support"
806 This option enables the complete Linux kernel ".config" file
807 contents to be saved in the kernel. It provides documentation
808 of which kernel options are used in a running kernel or in an
809 on-disk kernel. This information can be extracted from the kernel
810 image file with the script scripts/extract-ikconfig and used as
811 input to rebuild the current kernel or to build another kernel.
812 It can also be extracted from a running kernel by reading
813 /proc/config.gz if enabled (below).
816 bool "Enable access to .config through /proc/config.gz"
817 depends on IKCONFIG && PROC_FS
819 This option enables access to the kernel configuration file
820 through /proc/config.gz.
823 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
824 range 12 25 if !H8300
829 Select the minimal kernel log buffer size as a power of 2.
830 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
831 parameter, see below. Any higher size also might be forced
832 by "log_buf_len" boot parameter.
842 config LOG_CPU_MAX_BUF_SHIFT
843 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
846 default 12 if !BASE_SMALL
847 default 0 if BASE_SMALL
850 This option allows to increase the default ring buffer size
851 according to the number of CPUs. The value defines the contribution
852 of each CPU as a power of 2. The used space is typically only few
853 lines however it might be much more when problems are reported,
856 The increased size means that a new buffer has to be allocated and
857 the original static one is unused. It makes sense only on systems
858 with more CPUs. Therefore this value is used only when the sum of
859 contributions is greater than the half of the default kernel ring
860 buffer as defined by LOG_BUF_SHIFT. The default values are set
861 so that more than 64 CPUs are needed to trigger the allocation.
863 Also this option is ignored when "log_buf_len" kernel parameter is
864 used as it forces an exact (power of two) size of the ring buffer.
866 The number of possible CPUs is used for this computation ignoring
867 hotplugging making the computation optimal for the worst case
868 scenario while allowing a simple algorithm to be used from bootup.
870 Examples shift values and their meaning:
871 17 => 128 KB for each CPU
872 16 => 64 KB for each CPU
873 15 => 32 KB for each CPU
874 14 => 16 KB for each CPU
875 13 => 8 KB for each CPU
876 12 => 4 KB for each CPU
878 config NMI_LOG_BUF_SHIFT
879 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
882 depends on PRINTK_NMI
884 Select the size of a per-CPU buffer where NMI messages are temporary
885 stored. They are copied to the main log buffer in a safe context
886 to avoid a deadlock. The value defines the size as a power of 2.
888 NMI messages are rare and limited. The largest one is when
889 a backtrace is printed. It usually fits into 4KB. Select
890 8KB if you want to be on the safe side.
893 17 => 128 KB for each CPU
894 16 => 64 KB for each CPU
895 15 => 32 KB for each CPU
896 14 => 16 KB for each CPU
897 13 => 8 KB for each CPU
898 12 => 4 KB for each CPU
901 # Architectures with an unreliable sched_clock() should select this:
903 config HAVE_UNSTABLE_SCHED_CLOCK
906 config GENERIC_SCHED_CLOCK
910 # For architectures that want to enable the support for NUMA-affine scheduler
913 config ARCH_SUPPORTS_NUMA_BALANCING
917 # For architectures that prefer to flush all TLBs after a number of pages
918 # are unmapped instead of sending one IPI per page to flush. The architecture
919 # must provide guarantees on what happens if a clean TLB cache entry is
920 # written after the unmap. Details are in mm/rmap.c near the check for
921 # should_defer_flush. The architecture should also consider if the full flush
922 # and the refill costs are offset by the savings of sending fewer IPIs.
923 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
927 # For architectures that know their GCC __int128 support is sound
929 config ARCH_SUPPORTS_INT128
932 # For architectures that (ab)use NUMA to represent different memory regions
933 # all cpu-local but of different latencies, such as SuperH.
935 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
938 config NUMA_BALANCING
939 bool "Memory placement aware NUMA scheduler"
940 depends on ARCH_SUPPORTS_NUMA_BALANCING
941 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
942 depends on SMP && NUMA && MIGRATION
944 This option adds support for automatic NUMA aware memory/task placement.
945 The mechanism is quite primitive and is based on migrating memory when
946 it has references to the node the task is running on.
948 This system will be inactive on UMA systems.
950 config NUMA_BALANCING_DEFAULT_ENABLED
951 bool "Automatically enable NUMA aware memory/task placement"
953 depends on NUMA_BALANCING
955 If set, automatic NUMA balancing will be enabled if running on a NUMA
959 bool "Control Group support"
962 This option adds support for grouping sets of processes together, for
963 use with process control subsystems such as Cpusets, CFS, memory
964 controls or device isolation.
966 - Documentation/scheduler/sched-design-CFS.txt (CFS)
967 - Documentation/cgroup-v1/ (features for grouping, isolation
968 and resource control)
978 bool "Memory controller"
982 Provides control over the memory footprint of tasks in a cgroup.
985 bool "Swap controller"
986 depends on MEMCG && SWAP
988 Provides control over the swap space consumed by tasks in a cgroup.
990 config MEMCG_SWAP_ENABLED
991 bool "Swap controller enabled by default"
992 depends on MEMCG_SWAP
995 Memory Resource Controller Swap Extension comes with its price in
996 a bigger memory consumption. General purpose distribution kernels
997 which want to enable the feature but keep it disabled by default
998 and let the user enable it by swapaccount=1 boot command line
999 parameter should have this option unselected.
1000 For those who want to have the feature enabled by default should
1001 select this option (if, for some reason, they need to disable it
1002 then swapaccount=0 does the trick).
1005 bool "IO controller"
1009 Generic block IO controller cgroup interface. This is the common
1010 cgroup interface which should be used by various IO controlling
1013 Currently, CFQ IO scheduler uses it to recognize task groups and
1014 control disk bandwidth allocation (proportional time slice allocation)
1015 to such task groups. It is also used by bio throttling logic in
1016 block layer to implement upper limit in IO rates on a device.
1018 This option only enables generic Block IO controller infrastructure.
1019 One needs to also enable actual IO controlling logic/policy. For
1020 enabling proportional weight division of disk bandwidth in CFQ, set
1021 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1022 CONFIG_BLK_DEV_THROTTLING=y.
1024 See Documentation/cgroup-v1/blkio-controller.txt for more information.
1026 config DEBUG_BLK_CGROUP
1027 bool "IO controller debugging"
1028 depends on BLK_CGROUP
1031 Enable some debugging help. Currently it exports additional stat
1032 files in a cgroup which can be useful for debugging.
1034 config CGROUP_WRITEBACK
1036 depends on MEMCG && BLK_CGROUP
1039 menuconfig CGROUP_SCHED
1040 bool "CPU controller"
1043 This feature lets CPU scheduler recognize task groups and control CPU
1044 bandwidth allocation to such task groups. It uses cgroups to group
1048 config FAIR_GROUP_SCHED
1049 bool "Group scheduling for SCHED_OTHER"
1050 depends on CGROUP_SCHED
1051 default CGROUP_SCHED
1053 config CFS_BANDWIDTH
1054 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1055 depends on FAIR_GROUP_SCHED
1058 This option allows users to define CPU bandwidth rates (limits) for
1059 tasks running within the fair group scheduler. Groups with no limit
1060 set are considered to be unconstrained and will run with no
1062 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1064 config RT_GROUP_SCHED
1065 bool "Group scheduling for SCHED_RR/FIFO"
1066 depends on CGROUP_SCHED
1069 This feature lets you explicitly allocate real CPU bandwidth
1070 to task groups. If enabled, it will also make it impossible to
1071 schedule realtime tasks for non-root users until you allocate
1072 realtime bandwidth for them.
1073 See Documentation/scheduler/sched-rt-group.txt for more information.
1078 bool "PIDs controller"
1080 Provides enforcement of process number limits in the scope of a
1081 cgroup. Any attempt to fork more processes than is allowed in the
1082 cgroup will fail. PIDs are fundamentally a global resource because it
1083 is fairly trivial to reach PID exhaustion before you reach even a
1084 conservative kmemcg limit. As a result, it is possible to grind a
1085 system to halt without being limited by other cgroup policies. The
1086 PIDs controller is designed to stop this from happening.
1088 It should be noted that organisational operations (such as attaching
1089 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1090 since the PIDs limit only affects a process's ability to fork, not to
1093 config CGROUP_FREEZER
1094 bool "Freezer controller"
1096 Provides a way to freeze and unfreeze all tasks in a
1099 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1100 controller includes important in-kernel memory consumers per default.
1102 If you're using cgroup2, say N.
1104 config CGROUP_HUGETLB
1105 bool "HugeTLB controller"
1106 depends on HUGETLB_PAGE
1110 Provides a cgroup controller for HugeTLB pages.
1111 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1112 The limit is enforced during page fault. Since HugeTLB doesn't
1113 support page reclaim, enforcing the limit at page fault time implies
1114 that, the application will get SIGBUS signal if it tries to access
1115 HugeTLB pages beyond its limit. This requires the application to know
1116 beforehand how much HugeTLB pages it would require for its use. The
1117 control group is tracked in the third page lru pointer. This means
1118 that we cannot use the controller with huge page less than 3 pages.
1121 bool "Cpuset controller"
1123 This option will let you create and manage CPUSETs which
1124 allow dynamically partitioning a system into sets of CPUs and
1125 Memory Nodes and assigning tasks to run only within those sets.
1126 This is primarily useful on large SMP or NUMA systems.
1130 config PROC_PID_CPUSET
1131 bool "Include legacy /proc/<pid>/cpuset file"
1135 config CGROUP_DEVICE
1136 bool "Device controller"
1138 Provides a cgroup controller implementing whitelists for
1139 devices which a process in the cgroup can mknod or open.
1141 config CGROUP_CPUACCT
1142 bool "Simple CPU accounting controller"
1144 Provides a simple controller for monitoring the
1145 total CPU consumed by the tasks in a cgroup.
1148 bool "Perf controller"
1149 depends on PERF_EVENTS
1151 This option extends the perf per-cpu mode to restrict monitoring
1152 to threads which belong to the cgroup specified and run on the
1158 bool "Example controller"
1161 This option enables a simple controller that exports
1162 debugging information about the cgroups framework.
1168 config CHECKPOINT_RESTORE
1169 bool "Checkpoint/restore support" if EXPERT
1170 select PROC_CHILDREN
1173 Enables additional kernel features in a sake of checkpoint/restore.
1174 In particular it adds auxiliary prctl codes to setup process text,
1175 data and heap segment sizes, and a few additional /proc filesystem
1178 If unsure, say N here.
1180 menuconfig NAMESPACES
1181 bool "Namespaces support" if EXPERT
1182 depends on MULTIUSER
1185 Provides the way to make tasks work with different objects using
1186 the same id. For example same IPC id may refer to different objects
1187 or same user id or pid may refer to different tasks when used in
1188 different namespaces.
1193 bool "UTS namespace"
1196 In this namespace tasks see different info provided with the
1200 bool "IPC namespace"
1201 depends on (SYSVIPC || POSIX_MQUEUE)
1204 In this namespace tasks work with IPC ids which correspond to
1205 different IPC objects in different namespaces.
1208 bool "User namespace"
1211 This allows containers, i.e. vservers, to use user namespaces
1212 to provide different user info for different servers.
1214 When user namespaces are enabled in the kernel it is
1215 recommended that the MEMCG option also be enabled and that
1216 user-space use the memory control groups to limit the amount
1217 of memory a memory unprivileged users can use.
1222 bool "PID Namespaces"
1225 Support process id namespaces. This allows having multiple
1226 processes with the same pid as long as they are in different
1227 pid namespaces. This is a building block of containers.
1230 bool "Network namespace"
1234 Allow user space to create what appear to be multiple instances
1235 of the network stack.
1239 config SCHED_AUTOGROUP
1240 bool "Automatic process group scheduling"
1243 select FAIR_GROUP_SCHED
1245 This option optimizes the scheduler for common desktop workloads by
1246 automatically creating and populating task groups. This separation
1247 of workloads isolates aggressive CPU burners (like build jobs) from
1248 desktop applications. Task group autogeneration is currently based
1251 config SYSFS_DEPRECATED
1252 bool "Enable deprecated sysfs features to support old userspace tools"
1256 This option adds code that switches the layout of the "block" class
1257 devices, to not show up in /sys/class/block/, but only in
1260 This switch is only active when the sysfs.deprecated=1 boot option is
1261 passed or the SYSFS_DEPRECATED_V2 option is set.
1263 This option allows new kernels to run on old distributions and tools,
1264 which might get confused by /sys/class/block/. Since 2007/2008 all
1265 major distributions and tools handle this just fine.
1267 Recent distributions and userspace tools after 2009/2010 depend on
1268 the existence of /sys/class/block/, and will not work with this
1271 Only if you are using a new kernel on an old distribution, you might
1274 config SYSFS_DEPRECATED_V2
1275 bool "Enable deprecated sysfs features by default"
1278 depends on SYSFS_DEPRECATED
1280 Enable deprecated sysfs by default.
1282 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1285 Only if you are using a new kernel on an old distribution, you might
1286 need to say Y here. Even then, odds are you would not need it
1287 enabled, you can always pass the boot option if absolutely necessary.
1290 bool "Kernel->user space relay support (formerly relayfs)"
1293 This option enables support for relay interface support in
1294 certain file systems (such as debugfs).
1295 It is designed to provide an efficient mechanism for tools and
1296 facilities to relay large amounts of data from kernel space to
1301 config BLK_DEV_INITRD
1302 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1303 depends on BROKEN || !FRV
1305 The initial RAM filesystem is a ramfs which is loaded by the
1306 boot loader (loadlin or lilo) and that is mounted as root
1307 before the normal boot procedure. It is typically used to
1308 load modules needed to mount the "real" root file system,
1309 etc. See <file:Documentation/initrd.txt> for details.
1311 If RAM disk support (BLK_DEV_RAM) is also included, this
1312 also enables initial RAM disk (initrd) support and adds
1313 15 Kbytes (more on some other architectures) to the kernel size.
1319 source "usr/Kconfig"
1324 prompt "Compiler optimization level"
1325 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1327 config CC_OPTIMIZE_FOR_PERFORMANCE
1328 bool "Optimize for performance"
1330 This is the default optimization level for the kernel, building
1331 with the "-O2" compiler flag for best performance and most
1332 helpful compile-time warnings.
1334 config CC_OPTIMIZE_FOR_SIZE
1335 bool "Optimize for size"
1337 Enabling this option will pass "-Os" instead of "-O2" to
1338 your compiler resulting in a smaller kernel.
1353 config SYSCTL_EXCEPTION_TRACE
1356 Enable support for /proc/sys/debug/exception-trace.
1358 config SYSCTL_ARCH_UNALIGN_NO_WARN
1361 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1362 Allows arch to define/use @no_unaligned_warning to possibly warn
1363 about unaligned access emulation going on under the hood.
1365 config SYSCTL_ARCH_UNALIGN_ALLOW
1368 Enable support for /proc/sys/kernel/unaligned-trap
1369 Allows arches to define/use @unaligned_enabled to runtime toggle
1370 the unaligned access emulation.
1371 see arch/parisc/kernel/unaligned.c for reference
1373 config HAVE_PCSPKR_PLATFORM
1376 # interpreter that classic socket filters depend on
1381 bool "Configure standard kernel features (expert users)"
1382 # Unhide debug options, to make the on-by-default options visible
1385 This option allows certain base kernel options and settings
1386 to be disabled or tweaked. This is for specialized
1387 environments which can tolerate a "non-standard" kernel.
1388 Only use this if you really know what you are doing.
1391 bool "Enable 16-bit UID system calls" if EXPERT
1392 depends on HAVE_UID16 && MULTIUSER
1395 This enables the legacy 16-bit UID syscall wrappers.
1398 bool "Multiple users, groups and capabilities support" if EXPERT
1401 This option enables support for non-root users, groups and
1404 If you say N here, all processes will run with UID 0, GID 0, and all
1405 possible capabilities. Saying N here also compiles out support for
1406 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1409 If unsure, say Y here.
1411 config SGETMASK_SYSCALL
1412 bool "sgetmask/ssetmask syscalls support" if EXPERT
1413 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1415 sys_sgetmask and sys_ssetmask are obsolete system calls
1416 no longer supported in libc but still enabled by default in some
1419 If unsure, leave the default option here.
1421 config SYSFS_SYSCALL
1422 bool "Sysfs syscall support" if EXPERT
1425 sys_sysfs is an obsolete system call no longer supported in libc.
1426 Note that disabling this option is more secure but might break
1427 compatibility with some systems.
1429 If unsure say Y here.
1431 config SYSCTL_SYSCALL
1432 bool "Sysctl syscall support" if EXPERT
1433 depends on PROC_SYSCTL
1437 sys_sysctl uses binary paths that have been found challenging
1438 to properly maintain and use. The interface in /proc/sys
1439 using paths with ascii names is now the primary path to this
1442 Almost nothing using the binary sysctl interface so if you are
1443 trying to save some space it is probably safe to disable this,
1444 making your kernel marginally smaller.
1446 If unsure say N here.
1449 bool "Load all symbols for debugging/ksymoops" if EXPERT
1452 Say Y here to let the kernel print out symbolic crash information and
1453 symbolic stack backtraces. This increases the size of the kernel
1454 somewhat, as all symbols have to be loaded into the kernel image.
1457 bool "Include all symbols in kallsyms"
1458 depends on DEBUG_KERNEL && KALLSYMS
1460 Normally kallsyms only contains the symbols of functions for nicer
1461 OOPS messages and backtraces (i.e., symbols from the text and inittext
1462 sections). This is sufficient for most cases. And only in very rare
1463 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1464 names of variables from the data sections, etc).
1466 This option makes sure that all symbols are loaded into the kernel
1467 image (i.e., symbols from all sections) in cost of increased kernel
1468 size (depending on the kernel configuration, it may be 300KiB or
1469 something like this).
1471 Say N unless you really need all symbols.
1473 config KALLSYMS_ABSOLUTE_PERCPU
1476 default X86_64 && SMP
1478 config KALLSYMS_BASE_RELATIVE
1481 default !IA64 && !(TILE && 64BIT)
1483 Instead of emitting them as absolute values in the native word size,
1484 emit the symbol references in the kallsyms table as 32-bit entries,
1485 each containing a relative value in the range [base, base + U32_MAX]
1486 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1487 an absolute value in the range [0, S32_MAX] or a relative value in the
1488 range [base, base + S32_MAX], where base is the lowest relative symbol
1489 address encountered in the image.
1491 On 64-bit builds, this reduces the size of the address table by 50%,
1492 but more importantly, it results in entries whose values are build
1493 time constants, and no relocation pass is required at runtime to fix
1494 up the entries based on the runtime load address of the kernel.
1498 bool "Enable support for printk" if EXPERT
1501 This option enables normal printk support. Removing it
1502 eliminates most of the message strings from the kernel image
1503 and makes the kernel more or less silent. As this makes it
1504 very difficult to diagnose system problems, saying N here is
1505 strongly discouraged.
1513 bool "BUG() support" if EXPERT
1516 Disabling this option eliminates support for BUG and WARN, reducing
1517 the size of your kernel image and potentially quietly ignoring
1518 numerous fatal conditions. You should only consider disabling this
1519 option for embedded systems with no facilities for reporting errors.
1525 bool "Enable ELF core dumps" if EXPERT
1527 Enable support for generating core dumps. Disabling saves about 4k.
1530 config PCSPKR_PLATFORM
1531 bool "Enable PC-Speaker support" if EXPERT
1532 depends on HAVE_PCSPKR_PLATFORM
1536 This option allows to disable the internal PC-Speaker
1537 support, saving some memory.
1541 bool "Enable full-sized data structures for core" if EXPERT
1543 Disabling this option reduces the size of miscellaneous core
1544 kernel data structures. This saves memory on small machines,
1545 but may reduce performance.
1548 bool "Enable futex support" if EXPERT
1552 Disabling this option will cause the kernel to be built without
1553 support for "fast userspace mutexes". The resulting kernel may not
1554 run glibc-based applications correctly.
1556 config HAVE_FUTEX_CMPXCHG
1560 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1561 is implemented and always working. This removes a couple of runtime
1565 bool "Enable eventpoll support" if EXPERT
1569 Disabling this option will cause the kernel to be built without
1570 support for epoll family of system calls.
1573 bool "Enable signalfd() system call" if EXPERT
1577 Enable the signalfd() system call that allows to receive signals
1578 on a file descriptor.
1583 bool "Enable timerfd() system call" if EXPERT
1587 Enable the timerfd() system call that allows to receive timer
1588 events on a file descriptor.
1593 bool "Enable eventfd() system call" if EXPERT
1597 Enable the eventfd() system call that allows to receive both
1598 kernel notification (ie. KAIO) or userspace notifications.
1602 # syscall, maps, verifier
1604 bool "Enable bpf() system call"
1609 Enable the bpf() system call that allows to manipulate eBPF
1610 programs and maps via file descriptors.
1612 config BPF_JIT_ALWAYS_ON
1613 bool "Permanently enable BPF JIT and remove BPF interpreter"
1614 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
1616 Enables BPF JIT and removes BPF interpreter to avoid
1617 speculative execution of BPF instructions by the interpreter
1620 bool "Use full shmem filesystem" if EXPERT
1624 The shmem is an internal filesystem used to manage shared memory.
1625 It is backed by swap and manages resource limits. It is also exported
1626 to userspace as tmpfs if TMPFS is enabled. Disabling this
1627 option replaces shmem and tmpfs with the much simpler ramfs code,
1628 which may be appropriate on small systems without swap.
1631 bool "Enable AIO support" if EXPERT
1634 This option enables POSIX asynchronous I/O which may by used
1635 by some high performance threaded applications. Disabling
1636 this option saves about 7k.
1638 config ADVISE_SYSCALLS
1639 bool "Enable madvise/fadvise syscalls" if EXPERT
1642 This option enables the madvise and fadvise syscalls, used by
1643 applications to advise the kernel about their future memory or file
1644 usage, improving performance. If building an embedded system where no
1645 applications use these syscalls, you can disable this option to save
1649 bool "Enable userfaultfd() system call"
1653 Enable the userfaultfd() system call that allows to intercept and
1654 handle page faults in userland.
1658 bool "Enable PCI quirk workarounds" if EXPERT
1661 This enables workarounds for various PCI chipset
1662 bugs/quirks. Disable this only if your target machine is
1663 unaffected by PCI quirks.
1666 bool "Enable membarrier() system call" if EXPERT
1669 Enable the membarrier() system call that allows issuing memory
1670 barriers across all running threads, which can be used to distribute
1671 the cost of user-space memory barriers asymmetrically by transforming
1672 pairs of memory barriers into pairs consisting of membarrier() and a
1678 bool "Embedded system"
1679 option allnoconfig_y
1682 This option should be enabled if compiling the kernel for
1683 an embedded system so certain expert options are available
1686 config HAVE_PERF_EVENTS
1689 See tools/perf/design.txt for details.
1691 config PERF_USE_VMALLOC
1694 See tools/perf/design.txt for details
1696 menu "Kernel Performance Events And Counters"
1699 bool "Kernel performance events and counters"
1700 default y if PROFILING
1701 depends on HAVE_PERF_EVENTS
1706 Enable kernel support for various performance events provided
1707 by software and hardware.
1709 Software events are supported either built-in or via the
1710 use of generic tracepoints.
1712 Most modern CPUs support performance events via performance
1713 counter registers. These registers count the number of certain
1714 types of hw events: such as instructions executed, cachemisses
1715 suffered, or branches mis-predicted - without slowing down the
1716 kernel or applications. These registers can also trigger interrupts
1717 when a threshold number of events have passed - and can thus be
1718 used to profile the code that runs on that CPU.
1720 The Linux Performance Event subsystem provides an abstraction of
1721 these software and hardware event capabilities, available via a
1722 system call and used by the "perf" utility in tools/perf/. It
1723 provides per task and per CPU counters, and it provides event
1724 capabilities on top of those.
1728 config DEBUG_PERF_USE_VMALLOC
1730 bool "Debug: use vmalloc to back perf mmap() buffers"
1731 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1732 select PERF_USE_VMALLOC
1734 Use vmalloc memory to back perf mmap() buffers.
1736 Mostly useful for debugging the vmalloc code on platforms
1737 that don't require it.
1743 config VM_EVENT_COUNTERS
1745 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1747 VM event counters are needed for event counts to be shown.
1748 This option allows the disabling of the VM event counters
1749 on EXPERT systems. /proc/vmstat will only show page counts
1750 if VM event counters are disabled.
1754 bool "Enable SLUB debugging support" if EXPERT
1755 depends on SLUB && SYSFS
1757 SLUB has extensive debug support features. Disabling these can
1758 result in significant savings in code size. This also disables
1759 SLUB sysfs support. /sys/slab will not exist and there will be
1760 no support for cache validation etc.
1763 bool "Disable heap randomization"
1766 Randomizing heap placement makes heap exploits harder, but it
1767 also breaks ancient binaries (including anything libc5 based).
1768 This option changes the bootup default to heap randomization
1769 disabled, and can be overridden at runtime by setting
1770 /proc/sys/kernel/randomize_va_space to 2.
1772 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1775 prompt "Choose SLAB allocator"
1778 This option allows to select a slab allocator.
1782 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1784 The regular slab allocator that is established and known to work
1785 well in all environments. It organizes cache hot objects in
1786 per cpu and per node queues.
1789 bool "SLUB (Unqueued Allocator)"
1790 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1792 SLUB is a slab allocator that minimizes cache line usage
1793 instead of managing queues of cached objects (SLAB approach).
1794 Per cpu caching is realized using slabs of objects instead
1795 of queues of objects. SLUB can use memory efficiently
1796 and has enhanced diagnostics. SLUB is the default choice for
1801 bool "SLOB (Simple Allocator)"
1803 SLOB replaces the stock allocator with a drastically simpler
1804 allocator. SLOB is generally more space efficient but
1805 does not perform as well on large systems.
1809 config SLAB_FREELIST_RANDOM
1811 depends on SLAB || SLUB
1812 bool "SLAB freelist randomization"
1814 Randomizes the freelist order used on creating new pages. This
1815 security feature reduces the predictability of the kernel slab
1816 allocator against heap overflows.
1818 config SLUB_CPU_PARTIAL
1820 depends on SLUB && SMP
1821 bool "SLUB per cpu partial cache"
1823 Per cpu partial caches accellerate objects allocation and freeing
1824 that is local to a processor at the price of more indeterminism
1825 in the latency of the free. On overflow these caches will be cleared
1826 which requires the taking of locks that may cause latency spikes.
1827 Typically one would choose no for a realtime system.
1829 config MMAP_ALLOW_UNINITIALIZED
1830 bool "Allow mmapped anonymous memory to be uninitialized"
1831 depends on EXPERT && !MMU
1834 Normally, and according to the Linux spec, anonymous memory obtained
1835 from mmap() has it's contents cleared before it is passed to
1836 userspace. Enabling this config option allows you to request that
1837 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1838 providing a huge performance boost. If this option is not enabled,
1839 then the flag will be ignored.
1841 This is taken advantage of by uClibc's malloc(), and also by
1842 ELF-FDPIC binfmt's brk and stack allocator.
1844 Because of the obvious security issues, this option should only be
1845 enabled on embedded devices where you control what is run in
1846 userspace. Since that isn't generally a problem on no-MMU systems,
1847 it is normally safe to say Y here.
1849 See Documentation/nommu-mmap.txt for more information.
1851 config SYSTEM_DATA_VERIFICATION
1853 select SYSTEM_TRUSTED_KEYRING
1857 select ASYMMETRIC_KEY_TYPE
1858 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1861 select X509_CERTIFICATE_PARSER
1862 select PKCS7_MESSAGE_PARSER
1864 Provide PKCS#7 message verification using the contents of the system
1865 trusted keyring to provide public keys. This then can be used for
1866 module verification, kexec image verification and firmware blob
1870 bool "Profiling support"
1872 Say Y here to enable the extended profiling support mechanisms used
1873 by profilers such as OProfile.
1876 # Place an empty function call at each tracepoint site. Can be
1877 # dynamically changed for a probe function.
1882 source "arch/Kconfig"
1884 endmenu # General setup
1886 config HAVE_GENERIC_DMA_COHERENT
1893 depends on SLAB || SLUB_DEBUG
1901 default 0 if BASE_FULL
1902 default 1 if !BASE_FULL
1905 bool "Enable loadable module support"
1908 Kernel modules are small pieces of compiled code which can
1909 be inserted in the running kernel, rather than being
1910 permanently built into the kernel. You use the "modprobe"
1911 tool to add (and sometimes remove) them. If you say Y here,
1912 many parts of the kernel can be built as modules (by
1913 answering M instead of Y where indicated): this is most
1914 useful for infrequently used options which are not required
1915 for booting. For more information, see the man pages for
1916 modprobe, lsmod, modinfo, insmod and rmmod.
1918 If you say Y here, you will need to run "make
1919 modules_install" to put the modules under /lib/modules/
1920 where modprobe can find them (you may need to be root to do
1927 config MODULE_FORCE_LOAD
1928 bool "Forced module loading"
1931 Allow loading of modules without version information (ie. modprobe
1932 --force). Forced module loading sets the 'F' (forced) taint flag and
1933 is usually a really bad idea.
1935 config MODULE_UNLOAD
1936 bool "Module unloading"
1938 Without this option you will not be able to unload any
1939 modules (note that some modules may not be unloadable
1940 anyway), which makes your kernel smaller, faster
1941 and simpler. If unsure, say Y.
1943 config MODULE_FORCE_UNLOAD
1944 bool "Forced module unloading"
1945 depends on MODULE_UNLOAD
1947 This option allows you to force a module to unload, even if the
1948 kernel believes it is unsafe: the kernel will remove the module
1949 without waiting for anyone to stop using it (using the -f option to
1950 rmmod). This is mainly for kernel developers and desperate users.
1954 bool "Module versioning support"
1956 Usually, you have to use modules compiled with your kernel.
1957 Saying Y here makes it sometimes possible to use modules
1958 compiled for different kernels, by adding enough information
1959 to the modules to (hopefully) spot any changes which would
1960 make them incompatible with the kernel you are running. If
1963 config MODULE_SRCVERSION_ALL
1964 bool "Source checksum for all modules"
1966 Modules which contain a MODULE_VERSION get an extra "srcversion"
1967 field inserted into their modinfo section, which contains a
1968 sum of the source files which made it. This helps maintainers
1969 see exactly which source was used to build a module (since
1970 others sometimes change the module source without updating
1971 the version). With this option, such a "srcversion" field
1972 will be created for all modules. If unsure, say N.
1975 bool "Module signature verification"
1977 select SYSTEM_DATA_VERIFICATION
1979 Check modules for valid signatures upon load: the signature
1980 is simply appended to the module. For more information see
1981 Documentation/module-signing.txt.
1983 Note that this option adds the OpenSSL development packages as a
1984 kernel build dependency so that the signing tool can use its crypto
1987 !!!WARNING!!! If you enable this option, you MUST make sure that the
1988 module DOES NOT get stripped after being signed. This includes the
1989 debuginfo strip done by some packagers (such as rpmbuild) and
1990 inclusion into an initramfs that wants the module size reduced.
1992 config MODULE_SIG_FORCE
1993 bool "Require modules to be validly signed"
1994 depends on MODULE_SIG
1996 Reject unsigned modules or signed modules for which we don't have a
1997 key. Without this, such modules will simply taint the kernel.
1999 config MODULE_SIG_ALL
2000 bool "Automatically sign all modules"
2002 depends on MODULE_SIG
2004 Sign all modules during make modules_install. Without this option,
2005 modules must be signed manually, using the scripts/sign-file tool.
2007 comment "Do not forget to sign required modules with scripts/sign-file"
2008 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2011 prompt "Which hash algorithm should modules be signed with?"
2012 depends on MODULE_SIG
2014 This determines which sort of hashing algorithm will be used during
2015 signature generation. This algorithm _must_ be built into the kernel
2016 directly so that signature verification can take place. It is not
2017 possible to load a signed module containing the algorithm to check
2018 the signature on that module.
2020 config MODULE_SIG_SHA1
2021 bool "Sign modules with SHA-1"
2024 config MODULE_SIG_SHA224
2025 bool "Sign modules with SHA-224"
2026 select CRYPTO_SHA256
2028 config MODULE_SIG_SHA256
2029 bool "Sign modules with SHA-256"
2030 select CRYPTO_SHA256
2032 config MODULE_SIG_SHA384
2033 bool "Sign modules with SHA-384"
2034 select CRYPTO_SHA512
2036 config MODULE_SIG_SHA512
2037 bool "Sign modules with SHA-512"
2038 select CRYPTO_SHA512
2042 config MODULE_SIG_HASH
2044 depends on MODULE_SIG
2045 default "sha1" if MODULE_SIG_SHA1
2046 default "sha224" if MODULE_SIG_SHA224
2047 default "sha256" if MODULE_SIG_SHA256
2048 default "sha384" if MODULE_SIG_SHA384
2049 default "sha512" if MODULE_SIG_SHA512
2051 config MODULE_COMPRESS
2052 bool "Compress modules on installation"
2056 Compresses kernel modules when 'make modules_install' is run; gzip or
2057 xz depending on "Compression algorithm" below.
2059 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2061 Out-of-tree kernel modules installed using Kbuild will also be
2062 compressed upon installation.
2064 Note: for modules inside an initrd or initramfs, it's more efficient
2065 to compress the whole initrd or initramfs instead.
2067 Note: This is fully compatible with signed modules.
2072 prompt "Compression algorithm"
2073 depends on MODULE_COMPRESS
2074 default MODULE_COMPRESS_GZIP
2076 This determines which sort of compression will be used during
2077 'make modules_install'.
2079 GZIP (default) and XZ are supported.
2081 config MODULE_COMPRESS_GZIP
2084 config MODULE_COMPRESS_XZ
2089 config TRIM_UNUSED_KSYMS
2090 bool "Trim unused exported kernel symbols"
2091 depends on MODULES && !UNUSED_SYMBOLS
2093 The kernel and some modules make many symbols available for
2094 other modules to use via EXPORT_SYMBOL() and variants. Depending
2095 on the set of modules being selected in your kernel configuration,
2096 many of those exported symbols might never be used.
2098 This option allows for unused exported symbols to be dropped from
2099 the build. In turn, this provides the compiler more opportunities
2100 (especially when using LTO) for optimizing the code and reducing
2101 binary size. This might have some security advantages as well.
2103 If unsure, or if you need to build out-of-tree modules, say N.
2107 config MODULES_TREE_LOOKUP
2109 depends on PERF_EVENTS || TRACING
2111 config INIT_ALL_POSSIBLE
2114 Back when each arch used to define their own cpu_online_mask and
2115 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2116 with all 1s, and others with all 0s. When they were centralised,
2117 it was better to provide this option than to break all the archs
2118 and have several arch maintainers pursuing me down dark alleys.
2120 source "block/Kconfig"
2122 config PREEMPT_NOTIFIERS
2132 Build a simple ASN.1 grammar compiler that produces a bytecode output
2133 that can be interpreted by the ASN.1 stream decoder and used to
2134 inform it as to what tags are to be expected in a stream and what
2135 functions to call on what tags.
2137 source "kernel/Kconfig.locks"
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