7 option env="KERNELVERSION"
13 default "/lib/modules/$UNAME_RELEASE/.config"
14 default "/etc/kernel-config"
15 default "/boot/config-$UNAME_RELEASE"
16 default "$ARCH_DEFCONFIG"
17 default "arch/$ARCH/defconfig"
26 config BUILDTIME_EXTABLE_SORT
36 depends on BROKEN || !SMP
39 config INIT_ENV_ARG_LIMIT
44 Maximum of each of the number of arguments and environment
45 variables passed to init from the kernel command line.
49 string "Cross-compiler tool prefix"
51 Same as running 'make CROSS_COMPILE=prefix-' but stored for
52 default make runs in this kernel build directory. You don't
53 need to set this unless you want the configured kernel build
54 directory to select the cross-compiler automatically.
57 bool "Compile also drivers which will not load"
60 Some drivers can be compiled on a different platform than they are
61 intended to be run on. Despite they cannot be loaded there (or even
62 when they load they cannot be used due to missing HW support),
63 developers still, opposing to distributors, might want to build such
64 drivers to compile-test them.
66 If you are a developer and want to build everything available, say Y
67 here. If you are a user/distributor, say N here to exclude useless
68 drivers to be distributed.
71 string "Local version - append to kernel release"
73 Append an extra string to the end of your kernel version.
74 This will show up when you type uname, for example.
75 The string you set here will be appended after the contents of
76 any files with a filename matching localversion* in your
77 object and source tree, in that order. Your total string can
78 be a maximum of 64 characters.
80 config LOCALVERSION_AUTO
81 bool "Automatically append version information to the version string"
84 This will try to automatically determine if the current tree is a
85 release tree by looking for git tags that belong to the current
88 A string of the format -gxxxxxxxx will be added to the localversion
89 if a git-based tree is found. The string generated by this will be
90 appended after any matching localversion* files, and after the value
91 set in CONFIG_LOCALVERSION.
93 (The actual string used here is the first eight characters produced
94 by running the command:
96 $ git rev-parse --verify HEAD
98 which is done within the script "scripts/setlocalversion".)
100 config HAVE_KERNEL_GZIP
103 config HAVE_KERNEL_BZIP2
106 config HAVE_KERNEL_LZMA
109 config HAVE_KERNEL_XZ
112 config HAVE_KERNEL_LZO
115 config HAVE_KERNEL_LZ4
119 prompt "Kernel compression mode"
121 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
123 The linux kernel is a kind of self-extracting executable.
124 Several compression algorithms are available, which differ
125 in efficiency, compression and decompression speed.
126 Compression speed is only relevant when building a kernel.
127 Decompression speed is relevant at each boot.
129 If you have any problems with bzip2 or lzma compressed
130 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
131 version of this functionality (bzip2 only), for 2.4, was
132 supplied by Christian Ludwig)
134 High compression options are mostly useful for users, who
135 are low on disk space (embedded systems), but for whom ram
138 If in doubt, select 'gzip'
142 depends on HAVE_KERNEL_GZIP
144 The old and tried gzip compression. It provides a good balance
145 between compression ratio and decompression speed.
149 depends on HAVE_KERNEL_BZIP2
151 Its compression ratio and speed is intermediate.
152 Decompression speed is slowest among the choices. The kernel
153 size is about 10% smaller with bzip2, in comparison to gzip.
154 Bzip2 uses a large amount of memory. For modern kernels you
155 will need at least 8MB RAM or more for booting.
159 depends on HAVE_KERNEL_LZMA
161 This compression algorithm's ratio is best. Decompression speed
162 is between gzip and bzip2. Compression is slowest.
163 The kernel size is about 33% smaller with LZMA in comparison to gzip.
167 depends on HAVE_KERNEL_XZ
169 XZ uses the LZMA2 algorithm and instruction set specific
170 BCJ filters which can improve compression ratio of executable
171 code. The size of the kernel is about 30% smaller with XZ in
172 comparison to gzip. On architectures for which there is a BCJ
173 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
174 will create a few percent smaller kernel than plain LZMA.
176 The speed is about the same as with LZMA: The decompression
177 speed of XZ is better than that of bzip2 but worse than gzip
178 and LZO. Compression is slow.
182 depends on HAVE_KERNEL_LZO
184 Its compression ratio is the poorest among the choices. The kernel
185 size is about 10% bigger than gzip; however its speed
186 (both compression and decompression) is the fastest.
190 depends on HAVE_KERNEL_LZ4
192 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
193 A preliminary version of LZ4 de/compression tool is available at
194 <https://code.google.com/p/lz4/>.
196 Its compression ratio is worse than LZO. The size of the kernel
197 is about 8% bigger than LZO. But the decompression speed is
202 config DEFAULT_HOSTNAME
203 string "Default hostname"
206 This option determines the default system hostname before userspace
207 calls sethostname(2). The kernel traditionally uses "(none)" here,
208 but you may wish to use a different default here to make a minimal
209 system more usable with less configuration.
212 bool "Support for paging of anonymous memory (swap)"
213 depends on MMU && BLOCK
216 This option allows you to choose whether you want to have support
217 for so called swap devices or swap files in your kernel that are
218 used to provide more virtual memory than the actual RAM present
219 in your computer. If unsure say Y.
224 Inter Process Communication is a suite of library functions and
225 system calls which let processes (running programs) synchronize and
226 exchange information. It is generally considered to be a good thing,
227 and some programs won't run unless you say Y here. In particular, if
228 you want to run the DOS emulator dosemu under Linux (read the
229 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
230 you'll need to say Y here.
232 You can find documentation about IPC with "info ipc" and also in
233 section 6.4 of the Linux Programmer's Guide, available from
234 <http://www.tldp.org/guides.html>.
236 config SYSVIPC_SYSCTL
243 bool "POSIX Message Queues"
246 POSIX variant of message queues is a part of IPC. In POSIX message
247 queues every message has a priority which decides about succession
248 of receiving it by a process. If you want to compile and run
249 programs written e.g. for Solaris with use of its POSIX message
250 queues (functions mq_*) say Y here.
252 POSIX message queues are visible as a filesystem called 'mqueue'
253 and can be mounted somewhere if you want to do filesystem
254 operations on message queues.
258 config POSIX_MQUEUE_SYSCTL
260 depends on POSIX_MQUEUE
264 config CROSS_MEMORY_ATTACH
265 bool "Enable process_vm_readv/writev syscalls"
269 Enabling this option adds the system calls process_vm_readv and
270 process_vm_writev which allow a process with the correct privileges
271 to directly read from or write to another process' address space.
272 See the man page for more details.
275 bool "open by fhandle syscalls"
278 If you say Y here, a user level program will be able to map
279 file names to handle and then later use the handle for
280 different file system operations. This is useful in implementing
281 userspace file servers, which now track files using handles instead
282 of names. The handle would remain the same even if file names
283 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
287 bool "uselib syscall"
290 This option enables the uselib syscall, a system call used in the
291 dynamic linker from libc5 and earlier. glibc does not use this
292 system call. If you intend to run programs built on libc5 or
293 earlier, you may need to enable this syscall. Current systems
294 running glibc can safely disable this.
297 bool "Auditing support"
300 Enable auditing infrastructure that can be used with another
301 kernel subsystem, such as SELinux (which requires this for
302 logging of avc messages output). Does not do system-call
303 auditing without CONFIG_AUDITSYSCALL.
305 config HAVE_ARCH_AUDITSYSCALL
309 bool "Enable system-call auditing support"
310 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
311 default y if SECURITY_SELINUX
313 Enable low-overhead system-call auditing infrastructure that
314 can be used independently or with another kernel subsystem,
319 depends on AUDITSYSCALL
324 depends on AUDITSYSCALL
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
330 menu "CPU/Task time and stats accounting"
332 config VIRT_CPU_ACCOUNTING
336 prompt "Cputime accounting"
337 default TICK_CPU_ACCOUNTING if !PPC64
338 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
340 # Kind of a stub config for the pure tick based cputime accounting
341 config TICK_CPU_ACCOUNTING
342 bool "Simple tick based cputime accounting"
343 depends on !S390 && !NO_HZ_FULL
345 This is the basic tick based cputime accounting that maintains
346 statistics about user, system and idle time spent on per jiffies
351 config VIRT_CPU_ACCOUNTING_NATIVE
352 bool "Deterministic task and CPU time accounting"
353 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
354 select VIRT_CPU_ACCOUNTING
356 Select this option to enable more accurate task and CPU time
357 accounting. This is done by reading a CPU counter on each
358 kernel entry and exit and on transitions within the kernel
359 between system, softirq and hardirq state, so there is a
360 small performance impact. In the case of s390 or IBM POWER > 5,
361 this also enables accounting of stolen time on logically-partitioned
364 config VIRT_CPU_ACCOUNTING_GEN
365 bool "Full dynticks CPU time accounting"
366 depends on HAVE_CONTEXT_TRACKING
367 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
368 select VIRT_CPU_ACCOUNTING
369 select CONTEXT_TRACKING
371 Select this option to enable task and CPU time accounting on full
372 dynticks systems. This accounting is implemented by watching every
373 kernel-user boundaries using the context tracking subsystem.
374 The accounting is thus performed at the expense of some significant
377 For now this is only useful if you are working on the full
378 dynticks subsystem development.
382 config IRQ_TIME_ACCOUNTING
383 bool "Fine granularity task level IRQ time accounting"
384 depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
386 Select this option to enable fine granularity task irq time
387 accounting. This is done by reading a timestamp on each
388 transitions between softirq and hardirq state, so there can be a
389 small performance impact.
391 If in doubt, say N here.
395 config BSD_PROCESS_ACCT
396 bool "BSD Process Accounting"
398 If you say Y here, a user level program will be able to instruct the
399 kernel (via a special system call) to write process accounting
400 information to a file: whenever a process exits, information about
401 that process will be appended to the file by the kernel. The
402 information includes things such as creation time, owning user,
403 command name, memory usage, controlling terminal etc. (the complete
404 list is in the struct acct in <file:include/linux/acct.h>). It is
405 up to the user level program to do useful things with this
406 information. This is generally a good idea, so say Y.
408 config BSD_PROCESS_ACCT_V3
409 bool "BSD Process Accounting version 3 file format"
410 depends on BSD_PROCESS_ACCT
413 If you say Y here, the process accounting information is written
414 in a new file format that also logs the process IDs of each
415 process and it's parent. Note that this file format is incompatible
416 with previous v0/v1/v2 file formats, so you will need updated tools
417 for processing it. A preliminary version of these tools is available
418 at <http://www.gnu.org/software/acct/>.
421 bool "Export task/process statistics through netlink"
425 Export selected statistics for tasks/processes through the
426 generic netlink interface. Unlike BSD process accounting, the
427 statistics are available during the lifetime of tasks/processes as
428 responses to commands. Like BSD accounting, they are sent to user
433 config TASK_DELAY_ACCT
434 bool "Enable per-task delay accounting"
437 Collect information on time spent by a task waiting for system
438 resources like cpu, synchronous block I/O completion and swapping
439 in pages. Such statistics can help in setting a task's priorities
440 relative to other tasks for cpu, io, rss limits etc.
445 bool "Enable extended accounting over taskstats"
448 Collect extended task accounting data and send the data
449 to userland for processing over the taskstats interface.
453 config TASK_IO_ACCOUNTING
454 bool "Enable per-task storage I/O accounting"
455 depends on TASK_XACCT
457 Collect information on the number of bytes of storage I/O which this
462 endmenu # "CPU/Task time and stats accounting"
467 prompt "RCU Implementation"
471 bool "Tree-based hierarchical RCU"
472 depends on !PREEMPT && SMP
474 This option selects the RCU implementation that is
475 designed for very large SMP system with hundreds or
476 thousands of CPUs. It also scales down nicely to
480 bool "Preemptible tree-based hierarchical RCU"
483 This option selects the RCU implementation that is
484 designed for very large SMP systems with hundreds or
485 thousands of CPUs, but for which real-time response
486 is also required. It also scales down nicely to
489 Select this option if you are unsure.
492 bool "UP-only small-memory-footprint RCU"
493 depends on !PREEMPT && !SMP
495 This option selects the RCU implementation that is
496 designed for UP systems from which real-time response
497 is not required. This option greatly reduces the
498 memory footprint of RCU.
505 This option selects the sleepable version of RCU. This version
506 permits arbitrary sleeping or blocking within RCU read-side critical
510 bool "Task_based RCU implementation using voluntary context switch"
514 This option enables a task-based RCU implementation that uses
515 only voluntary context switch (not preemption!), idle, and
516 user-mode execution as quiescent states.
520 config RCU_STALL_COMMON
521 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
523 This option enables RCU CPU stall code that is common between
524 the TINY and TREE variants of RCU. The purpose is to allow
525 the tiny variants to disable RCU CPU stall warnings, while
526 making these warnings mandatory for the tree variants.
528 config CONTEXT_TRACKING
532 bool "Consider userspace as in RCU extended quiescent state"
533 depends on HAVE_CONTEXT_TRACKING && SMP
534 select CONTEXT_TRACKING
536 This option sets hooks on kernel / userspace boundaries and
537 puts RCU in extended quiescent state when the CPU runs in
538 userspace. It means that when a CPU runs in userspace, it is
539 excluded from the global RCU state machine and thus doesn't
540 try to keep the timer tick on for RCU.
542 Unless you want to hack and help the development of the full
543 dynticks mode, you shouldn't enable this option. It also
544 adds unnecessary overhead.
548 config CONTEXT_TRACKING_FORCE
549 bool "Force context tracking"
550 depends on CONTEXT_TRACKING
551 default y if !NO_HZ_FULL
553 The major pre-requirement for full dynticks to work is to
554 support the context tracking subsystem. But there are also
555 other dependencies to provide in order to make the full
558 This option stands for testing when an arch implements the
559 context tracking backend but doesn't yet fullfill all the
560 requirements to make the full dynticks feature working.
561 Without the full dynticks, there is no way to test the support
562 for context tracking and the subsystems that rely on it: RCU
563 userspace extended quiescent state and tickless cputime
564 accounting. This option copes with the absence of the full
565 dynticks subsystem by forcing the context tracking on all
568 Say Y only if you're working on the development of an
569 architecture backend for the context tracking.
571 Say N otherwise, this option brings an overhead that you
572 don't want in production.
576 int "Tree-based hierarchical RCU fanout value"
579 depends on TREE_RCU || PREEMPT_RCU
583 This option controls the fanout of hierarchical implementations
584 of RCU, allowing RCU to work efficiently on machines with
585 large numbers of CPUs. This value must be at least the fourth
586 root of NR_CPUS, which allows NR_CPUS to be insanely large.
587 The default value of RCU_FANOUT should be used for production
588 systems, but if you are stress-testing the RCU implementation
589 itself, small RCU_FANOUT values allow you to test large-system
590 code paths on small(er) systems.
592 Select a specific number if testing RCU itself.
593 Take the default if unsure.
595 config RCU_FANOUT_LEAF
596 int "Tree-based hierarchical RCU leaf-level fanout value"
597 range 2 RCU_FANOUT if 64BIT
598 range 2 RCU_FANOUT if !64BIT
599 depends on TREE_RCU || PREEMPT_RCU
602 This option controls the leaf-level fanout of hierarchical
603 implementations of RCU, and allows trading off cache misses
604 against lock contention. Systems that synchronize their
605 scheduling-clock interrupts for energy-efficiency reasons will
606 want the default because the smaller leaf-level fanout keeps
607 lock contention levels acceptably low. Very large systems
608 (hundreds or thousands of CPUs) will instead want to set this
609 value to the maximum value possible in order to reduce the
610 number of cache misses incurred during RCU's grace-period
611 initialization. These systems tend to run CPU-bound, and thus
612 are not helped by synchronized interrupts, and thus tend to
613 skew them, which reduces lock contention enough that large
614 leaf-level fanouts work well.
616 Select a specific number if testing RCU itself.
618 Select the maximum permissible value for large systems.
620 Take the default if unsure.
622 config RCU_FANOUT_EXACT
623 bool "Disable tree-based hierarchical RCU auto-balancing"
624 depends on TREE_RCU || PREEMPT_RCU
627 This option forces use of the exact RCU_FANOUT value specified,
628 regardless of imbalances in the hierarchy. This is useful for
629 testing RCU itself, and might one day be useful on systems with
630 strong NUMA behavior.
632 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
636 config RCU_FAST_NO_HZ
637 bool "Accelerate last non-dyntick-idle CPU's grace periods"
638 depends on NO_HZ_COMMON && SMP
641 This option permits CPUs to enter dynticks-idle state even if
642 they have RCU callbacks queued, and prevents RCU from waking
643 these CPUs up more than roughly once every four jiffies (by
644 default, you can adjust this using the rcutree.rcu_idle_gp_delay
645 parameter), thus improving energy efficiency. On the other
646 hand, this option increases the duration of RCU grace periods,
647 for example, slowing down synchronize_rcu().
649 Say Y if energy efficiency is critically important, and you
650 don't care about increased grace-period durations.
652 Say N if you are unsure.
654 config TREE_RCU_TRACE
655 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
658 This option provides tracing for the TREE_RCU and
659 PREEMPT_RCU implementations, permitting Makefile to
660 trivially select kernel/rcutree_trace.c.
663 bool "Enable RCU priority boosting"
664 depends on RT_MUTEXES && PREEMPT_RCU
667 This option boosts the priority of preempted RCU readers that
668 block the current preemptible RCU grace period for too long.
669 This option also prevents heavy loads from blocking RCU
670 callback invocation for all flavors of RCU.
672 Say Y here if you are working with real-time apps or heavy loads
673 Say N here if you are unsure.
675 config RCU_KTHREAD_PRIO
676 int "Real-time priority to use for RCU worker threads"
677 range 1 99 if RCU_BOOST
678 range 0 99 if !RCU_BOOST
679 default 1 if RCU_BOOST
680 default 0 if !RCU_BOOST
682 This option specifies the SCHED_FIFO priority value that will be
683 assigned to the rcuc/n and rcub/n threads and is also the value
684 used for RCU_BOOST (if enabled). If you are working with a
685 real-time application that has one or more CPU-bound threads
686 running at a real-time priority level, you should set
687 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
688 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
689 value of 1 is appropriate in the common case, which is real-time
690 applications that do not have any CPU-bound threads.
692 Some real-time applications might not have a single real-time
693 thread that saturates a given CPU, but instead might have
694 multiple real-time threads that, taken together, fully utilize
695 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
696 a priority higher than the lowest-priority thread that is
697 conspiring to prevent the CPU from running any non-real-time
698 tasks. For example, if one thread at priority 10 and another
699 thread at priority 5 are between themselves fully consuming
700 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
701 set to priority 6 or higher.
703 Specify the real-time priority, or take the default if unsure.
705 config RCU_BOOST_DELAY
706 int "Milliseconds to delay boosting after RCU grace-period start"
711 This option specifies the time to wait after the beginning of
712 a given grace period before priority-boosting preempted RCU
713 readers blocking that grace period. Note that any RCU reader
714 blocking an expedited RCU grace period is boosted immediately.
716 Accept the default if unsure.
719 bool "Offload RCU callback processing from boot-selected CPUs"
720 depends on TREE_RCU || PREEMPT_RCU
723 Use this option to reduce OS jitter for aggressive HPC or
724 real-time workloads. It can also be used to offload RCU
725 callback invocation to energy-efficient CPUs in battery-powered
726 asymmetric multiprocessors.
728 This option offloads callback invocation from the set of
729 CPUs specified at boot time by the rcu_nocbs parameter.
730 For each such CPU, a kthread ("rcuox/N") will be created to
731 invoke callbacks, where the "N" is the CPU being offloaded,
732 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
733 "s" for RCU-sched. Nothing prevents this kthread from running
734 on the specified CPUs, but (1) the kthreads may be preempted
735 between each callback, and (2) affinity or cgroups can be used
736 to force the kthreads to run on whatever set of CPUs is desired.
738 Say Y here if you want to help to debug reduced OS jitter.
739 Say N here if you are unsure.
742 prompt "Build-forced no-CBs CPUs"
743 default RCU_NOCB_CPU_NONE
744 depends on RCU_NOCB_CPU
746 This option allows no-CBs CPUs (whose RCU callbacks are invoked
747 from kthreads rather than from softirq context) to be specified
748 at build time. Additional no-CBs CPUs may be specified by
749 the rcu_nocbs= boot parameter.
751 config RCU_NOCB_CPU_NONE
752 bool "No build_forced no-CBs CPUs"
754 This option does not force any of the CPUs to be no-CBs CPUs.
755 Only CPUs designated by the rcu_nocbs= boot parameter will be
756 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
757 kthreads whose names begin with "rcuo". All other CPUs will
758 invoke their own RCU callbacks in softirq context.
760 Select this option if you want to choose no-CBs CPUs at
761 boot time, for example, to allow testing of different no-CBs
762 configurations without having to rebuild the kernel each time.
764 config RCU_NOCB_CPU_ZERO
765 bool "CPU 0 is a build_forced no-CBs CPU"
767 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
768 callbacks are invoked by a per-CPU kthread whose name begins
769 with "rcuo". Additional CPUs may be designated as no-CBs
770 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
771 All other CPUs will invoke their own RCU callbacks in softirq
774 Select this if CPU 0 needs to be a no-CBs CPU for real-time
775 or energy-efficiency reasons, but the real reason it exists
776 is to ensure that randconfig testing covers mixed systems.
778 config RCU_NOCB_CPU_ALL
779 bool "All CPUs are build_forced no-CBs CPUs"
781 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
782 boot parameter will be ignored. All CPUs' RCU callbacks will
783 be executed in the context of per-CPU rcuo kthreads created for
784 this purpose. Assuming that the kthreads whose names start with
785 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
786 on the remaining CPUs, but might decrease memory locality during
787 RCU-callback invocation, thus potentially degrading throughput.
789 Select this if all CPUs need to be no-CBs CPUs for real-time
790 or energy-efficiency reasons.
794 endmenu # "RCU Subsystem"
801 tristate "Kernel .config support"
804 This option enables the complete Linux kernel ".config" file
805 contents to be saved in the kernel. It provides documentation
806 of which kernel options are used in a running kernel or in an
807 on-disk kernel. This information can be extracted from the kernel
808 image file with the script scripts/extract-ikconfig and used as
809 input to rebuild the current kernel or to build another kernel.
810 It can also be extracted from a running kernel by reading
811 /proc/config.gz if enabled (below).
814 bool "Enable access to .config through /proc/config.gz"
815 depends on IKCONFIG && PROC_FS
817 This option enables access to the kernel configuration file
818 through /proc/config.gz.
821 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
826 Select the minimal kernel log buffer size as a power of 2.
827 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
828 parameter, see below. Any higher size also might be forced
829 by "log_buf_len" boot parameter.
839 config LOG_CPU_MAX_BUF_SHIFT
840 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
843 default 12 if !BASE_SMALL
844 default 0 if BASE_SMALL
847 This option allows to increase the default ring buffer size
848 according to the number of CPUs. The value defines the contribution
849 of each CPU as a power of 2. The used space is typically only few
850 lines however it might be much more when problems are reported,
853 The increased size means that a new buffer has to be allocated and
854 the original static one is unused. It makes sense only on systems
855 with more CPUs. Therefore this value is used only when the sum of
856 contributions is greater than the half of the default kernel ring
857 buffer as defined by LOG_BUF_SHIFT. The default values are set
858 so that more than 64 CPUs are needed to trigger the allocation.
860 Also this option is ignored when "log_buf_len" kernel parameter is
861 used as it forces an exact (power of two) size of the ring buffer.
863 The number of possible CPUs is used for this computation ignoring
864 hotplugging making the compuation optimal for the the worst case
865 scenerio while allowing a simple algorithm to be used from bootup.
867 Examples shift values and their meaning:
868 17 => 128 KB for each CPU
869 16 => 64 KB for each CPU
870 15 => 32 KB for each CPU
871 14 => 16 KB for each CPU
872 13 => 8 KB for each CPU
873 12 => 4 KB for each CPU
876 # Architectures with an unreliable sched_clock() should select this:
878 config HAVE_UNSTABLE_SCHED_CLOCK
881 config GENERIC_SCHED_CLOCK
885 # For architectures that want to enable the support for NUMA-affine scheduler
888 config ARCH_SUPPORTS_NUMA_BALANCING
892 # For architectures that know their GCC __int128 support is sound
894 config ARCH_SUPPORTS_INT128
897 # For architectures that (ab)use NUMA to represent different memory regions
898 # all cpu-local but of different latencies, such as SuperH.
900 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
903 config NUMA_BALANCING
904 bool "Memory placement aware NUMA scheduler"
905 depends on ARCH_SUPPORTS_NUMA_BALANCING
906 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
907 depends on SMP && NUMA && MIGRATION
909 This option adds support for automatic NUMA aware memory/task placement.
910 The mechanism is quite primitive and is based on migrating memory when
911 it has references to the node the task is running on.
913 This system will be inactive on UMA systems.
915 config NUMA_BALANCING_DEFAULT_ENABLED
916 bool "Automatically enable NUMA aware memory/task placement"
918 depends on NUMA_BALANCING
920 If set, automatic NUMA balancing will be enabled if running on a NUMA
924 bool "Control Group support"
927 This option adds support for grouping sets of processes together, for
928 use with process control subsystems such as Cpusets, CFS, memory
929 controls or device isolation.
931 - Documentation/scheduler/sched-design-CFS.txt (CFS)
932 - Documentation/cgroups/ (features for grouping, isolation
933 and resource control)
940 bool "Example debug cgroup subsystem"
943 This option enables a simple cgroup subsystem that
944 exports useful debugging information about the cgroups
949 config CGROUP_FREEZER
950 bool "Freezer cgroup subsystem"
952 Provides a way to freeze and unfreeze all tasks in a
956 bool "Device controller for cgroups"
958 Provides a cgroup implementing whitelists for devices which
959 a process in the cgroup can mknod or open.
962 bool "Cpuset support"
964 This option will let you create and manage CPUSETs which
965 allow dynamically partitioning a system into sets of CPUs and
966 Memory Nodes and assigning tasks to run only within those sets.
967 This is primarily useful on large SMP or NUMA systems.
971 config PROC_PID_CPUSET
972 bool "Include legacy /proc/<pid>/cpuset file"
976 config CGROUP_CPUACCT
977 bool "Simple CPU accounting cgroup subsystem"
979 Provides a simple Resource Controller for monitoring the
980 total CPU consumed by the tasks in a cgroup.
986 bool "Memory Resource Controller for Control Groups"
990 Provides a memory resource controller that manages both anonymous
991 memory and page cache. (See Documentation/cgroups/memory.txt)
994 bool "Memory Resource Controller Swap Extension"
995 depends on MEMCG && SWAP
997 Add swap management feature to memory resource controller. When you
998 enable this, you can limit mem+swap usage per cgroup. In other words,
999 when you disable this, memory resource controller has no cares to
1000 usage of swap...a process can exhaust all of the swap. This extension
1001 is useful when you want to avoid exhaustion swap but this itself
1002 adds more overheads and consumes memory for remembering information.
1003 Especially if you use 32bit system or small memory system, please
1004 be careful about enabling this. When memory resource controller
1005 is disabled by boot option, this will be automatically disabled and
1006 there will be no overhead from this. Even when you set this config=y,
1007 if boot option "swapaccount=0" is set, swap will not be accounted.
1008 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1009 size is 4096bytes, 512k per 1Gbytes of swap.
1010 config MEMCG_SWAP_ENABLED
1011 bool "Memory Resource Controller Swap Extension enabled by default"
1012 depends on MEMCG_SWAP
1015 Memory Resource Controller Swap Extension comes with its price in
1016 a bigger memory consumption. General purpose distribution kernels
1017 which want to enable the feature but keep it disabled by default
1018 and let the user enable it by swapaccount=1 boot command line
1019 parameter should have this option unselected.
1020 For those who want to have the feature enabled by default should
1021 select this option (if, for some reason, they need to disable it
1022 then swapaccount=0 does the trick).
1024 bool "Memory Resource Controller Kernel Memory accounting"
1026 depends on SLUB || SLAB
1028 The Kernel Memory extension for Memory Resource Controller can limit
1029 the amount of memory used by kernel objects in the system. Those are
1030 fundamentally different from the entities handled by the standard
1031 Memory Controller, which are page-based, and can be swapped. Users of
1032 the kmem extension can use it to guarantee that no group of processes
1033 will ever exhaust kernel resources alone.
1035 WARNING: Current implementation lacks reclaim support. That means
1036 allocation attempts will fail when close to the limit even if there
1037 are plenty of kmem available for reclaim. That makes this option
1038 unusable in real life so DO NOT SELECT IT unless for development
1041 config CGROUP_HUGETLB
1042 bool "HugeTLB Resource Controller for Control Groups"
1043 depends on HUGETLB_PAGE
1047 Provides a cgroup Resource Controller for HugeTLB pages.
1048 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1049 The limit is enforced during page fault. Since HugeTLB doesn't
1050 support page reclaim, enforcing the limit at page fault time implies
1051 that, the application will get SIGBUS signal if it tries to access
1052 HugeTLB pages beyond its limit. This requires the application to know
1053 beforehand how much HugeTLB pages it would require for its use. The
1054 control group is tracked in the third page lru pointer. This means
1055 that we cannot use the controller with huge page less than 3 pages.
1058 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1059 depends on PERF_EVENTS && CGROUPS
1061 This option extends the per-cpu mode to restrict monitoring to
1062 threads which belong to the cgroup specified and run on the
1067 menuconfig CGROUP_SCHED
1068 bool "Group CPU scheduler"
1071 This feature lets CPU scheduler recognize task groups and control CPU
1072 bandwidth allocation to such task groups. It uses cgroups to group
1076 config FAIR_GROUP_SCHED
1077 bool "Group scheduling for SCHED_OTHER"
1078 depends on CGROUP_SCHED
1079 default CGROUP_SCHED
1081 config CFS_BANDWIDTH
1082 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1083 depends on FAIR_GROUP_SCHED
1086 This option allows users to define CPU bandwidth rates (limits) for
1087 tasks running within the fair group scheduler. Groups with no limit
1088 set are considered to be unconstrained and will run with no
1090 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1092 config RT_GROUP_SCHED
1093 bool "Group scheduling for SCHED_RR/FIFO"
1094 depends on CGROUP_SCHED
1097 This feature lets you explicitly allocate real CPU bandwidth
1098 to task groups. If enabled, it will also make it impossible to
1099 schedule realtime tasks for non-root users until you allocate
1100 realtime bandwidth for them.
1101 See Documentation/scheduler/sched-rt-group.txt for more information.
1106 bool "Block IO controller"
1110 Generic block IO controller cgroup interface. This is the common
1111 cgroup interface which should be used by various IO controlling
1114 Currently, CFQ IO scheduler uses it to recognize task groups and
1115 control disk bandwidth allocation (proportional time slice allocation)
1116 to such task groups. It is also used by bio throttling logic in
1117 block layer to implement upper limit in IO rates on a device.
1119 This option only enables generic Block IO controller infrastructure.
1120 One needs to also enable actual IO controlling logic/policy. For
1121 enabling proportional weight division of disk bandwidth in CFQ, set
1122 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1123 CONFIG_BLK_DEV_THROTTLING=y.
1125 See Documentation/cgroups/blkio-controller.txt for more information.
1127 config DEBUG_BLK_CGROUP
1128 bool "Enable Block IO controller debugging"
1129 depends on BLK_CGROUP
1132 Enable some debugging help. Currently it exports additional stat
1133 files in a cgroup which can be useful for debugging.
1137 config CHECKPOINT_RESTORE
1138 bool "Checkpoint/restore support" if EXPERT
1141 Enables additional kernel features in a sake of checkpoint/restore.
1142 In particular it adds auxiliary prctl codes to setup process text,
1143 data and heap segment sizes, and a few additional /proc filesystem
1146 If unsure, say N here.
1148 menuconfig NAMESPACES
1149 bool "Namespaces support" if EXPERT
1152 Provides the way to make tasks work with different objects using
1153 the same id. For example same IPC id may refer to different objects
1154 or same user id or pid may refer to different tasks when used in
1155 different namespaces.
1160 bool "UTS namespace"
1163 In this namespace tasks see different info provided with the
1167 bool "IPC namespace"
1168 depends on (SYSVIPC || POSIX_MQUEUE)
1171 In this namespace tasks work with IPC ids which correspond to
1172 different IPC objects in different namespaces.
1175 bool "User namespace"
1178 This allows containers, i.e. vservers, to use user namespaces
1179 to provide different user info for different servers.
1181 When user namespaces are enabled in the kernel it is
1182 recommended that the MEMCG and MEMCG_KMEM options also be
1183 enabled and that user-space use the memory control groups to
1184 limit the amount of memory a memory unprivileged users can
1190 bool "PID Namespaces"
1193 Support process id namespaces. This allows having multiple
1194 processes with the same pid as long as they are in different
1195 pid namespaces. This is a building block of containers.
1198 bool "Network namespace"
1202 Allow user space to create what appear to be multiple instances
1203 of the network stack.
1207 config SCHED_AUTOGROUP
1208 bool "Automatic process group scheduling"
1211 select FAIR_GROUP_SCHED
1213 This option optimizes the scheduler for common desktop workloads by
1214 automatically creating and populating task groups. This separation
1215 of workloads isolates aggressive CPU burners (like build jobs) from
1216 desktop applications. Task group autogeneration is currently based
1219 config SYSFS_DEPRECATED
1220 bool "Enable deprecated sysfs features to support old userspace tools"
1224 This option adds code that switches the layout of the "block" class
1225 devices, to not show up in /sys/class/block/, but only in
1228 This switch is only active when the sysfs.deprecated=1 boot option is
1229 passed or the SYSFS_DEPRECATED_V2 option is set.
1231 This option allows new kernels to run on old distributions and tools,
1232 which might get confused by /sys/class/block/. Since 2007/2008 all
1233 major distributions and tools handle this just fine.
1235 Recent distributions and userspace tools after 2009/2010 depend on
1236 the existence of /sys/class/block/, and will not work with this
1239 Only if you are using a new kernel on an old distribution, you might
1242 config SYSFS_DEPRECATED_V2
1243 bool "Enable deprecated sysfs features by default"
1246 depends on SYSFS_DEPRECATED
1248 Enable deprecated sysfs by default.
1250 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1253 Only if you are using a new kernel on an old distribution, you might
1254 need to say Y here. Even then, odds are you would not need it
1255 enabled, you can always pass the boot option if absolutely necessary.
1258 bool "Kernel->user space relay support (formerly relayfs)"
1260 This option enables support for relay interface support in
1261 certain file systems (such as debugfs).
1262 It is designed to provide an efficient mechanism for tools and
1263 facilities to relay large amounts of data from kernel space to
1268 config BLK_DEV_INITRD
1269 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1270 depends on BROKEN || !FRV
1272 The initial RAM filesystem is a ramfs which is loaded by the
1273 boot loader (loadlin or lilo) and that is mounted as root
1274 before the normal boot procedure. It is typically used to
1275 load modules needed to mount the "real" root file system,
1276 etc. See <file:Documentation/initrd.txt> for details.
1278 If RAM disk support (BLK_DEV_RAM) is also included, this
1279 also enables initial RAM disk (initrd) support and adds
1280 15 Kbytes (more on some other architectures) to the kernel size.
1286 source "usr/Kconfig"
1290 config CC_OPTIMIZE_FOR_SIZE
1291 bool "Optimize for size"
1293 Enabling this option will pass "-Os" instead of "-O2" to
1294 your compiler resulting in a smaller kernel.
1299 bool "Enable gcc link time optimization (LTO)"
1300 # Only tested on X86 for now. For other architectures you likely
1301 # have to fix some things first, like adding asmlinkages etc.
1303 # lto does not support excluding flags for specific files
1304 # right now. Can be removed if that is fixed.
1305 depends on !FUNCTION_TRACER
1307 With this option gcc will do whole program optimizations for
1308 the whole kernel and module. This increases compile time, but can
1309 lead to better code. It allows gcc to inline functions between
1310 different files and do other optimization. It might also trigger
1311 bugs due to more aggressive optimization. It allows gcc to drop unused
1312 code. On smaller monolithic kernel configurations
1313 it usually leads to smaller kernels, especially when modules
1316 With this option gcc will also do some global checking over
1317 different source files. It also disables a number of kernel
1320 This option is recommended for release builds. With LTO
1321 the kernel always has to be re-optimized (but not re-parsed)
1324 This requires a gcc 4.8 or later compiler and
1325 Linux binutils 2.21.51.0.3 or later. gcc 4.9 builds significantly
1326 faster than 4.8 It does not currently work with a FSF release of
1327 binutils or with the gold linker.
1329 On larger configurations this may need more than 4GB of RAM.
1330 It will likely not work on those with a 32bit compiler.
1332 When the toolchain support is not available this will (hopefully)
1333 be automatically disabled.
1335 For more information see Documentation/lto-build
1338 bool "Disable LTO again"
1342 This option is merely here so that allyesconfig or allmodconfig do
1343 not enable LTO. If you want to actually use LTO do not enable.
1348 depends on LTO_MENU && !LTO_DISABLE
1351 bool "Enable LTO compile time debugging"
1354 Enable LTO debugging in the compiler. The compiler dumps
1355 some log files that make it easier to figure out LTO
1356 behavior. The log files also allow to reconstruct
1357 the global inlining and a global callgraph.
1358 They however add some (single threaded) cost to the
1359 compilation. When in doubt do not enable.
1362 bool "Allow aggressive cloning for function specialization"
1365 Allow the compiler to clone and specialize functions for specific
1366 arguments when it determines these arguments are very commonly
1367 called. Experimential. Will increase text size.
1378 config SYSCTL_EXCEPTION_TRACE
1381 Enable support for /proc/sys/debug/exception-trace.
1383 config SYSCTL_ARCH_UNALIGN_NO_WARN
1386 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1387 Allows arch to define/use @no_unaligned_warning to possibly warn
1388 about unaligned access emulation going on under the hood.
1390 config SYSCTL_ARCH_UNALIGN_ALLOW
1393 Enable support for /proc/sys/kernel/unaligned-trap
1394 Allows arches to define/use @unaligned_enabled to runtime toggle
1395 the unaligned access emulation.
1396 see arch/parisc/kernel/unaligned.c for reference
1398 config HAVE_PCSPKR_PLATFORM
1401 # interpreter that classic socket filters depend on
1406 bool "Configure standard kernel features (expert users)"
1407 # Unhide debug options, to make the on-by-default options visible
1410 This option allows certain base kernel options and settings
1411 to be disabled or tweaked. This is for specialized
1412 environments which can tolerate a "non-standard" kernel.
1413 Only use this if you really know what you are doing.
1416 bool "Enable 16-bit UID system calls" if EXPERT
1417 depends on HAVE_UID16
1420 This enables the legacy 16-bit UID syscall wrappers.
1422 config SGETMASK_SYSCALL
1423 bool "sgetmask/ssetmask syscalls support" if EXPERT
1424 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1426 sys_sgetmask and sys_ssetmask are obsolete system calls
1427 no longer supported in libc but still enabled by default in some
1430 If unsure, leave the default option here.
1432 config SYSFS_SYSCALL
1433 bool "Sysfs syscall support" if EXPERT
1436 sys_sysfs is an obsolete system call no longer supported in libc.
1437 Note that disabling this option is more secure but might break
1438 compatibility with some systems.
1440 If unsure say Y here.
1442 config SYSCTL_SYSCALL
1443 bool "Sysctl syscall support" if EXPERT
1444 depends on PROC_SYSCTL
1448 sys_sysctl uses binary paths that have been found challenging
1449 to properly maintain and use. The interface in /proc/sys
1450 using paths with ascii names is now the primary path to this
1453 Almost nothing using the binary sysctl interface so if you are
1454 trying to save some space it is probably safe to disable this,
1455 making your kernel marginally smaller.
1457 If unsure say N here.
1460 bool "Load all symbols for debugging/ksymoops" if EXPERT
1463 Say Y here to let the kernel print out symbolic crash information and
1464 symbolic stack backtraces. This increases the size of the kernel
1465 somewhat, as all symbols have to be loaded into the kernel image.
1468 bool "Include all symbols in kallsyms"
1469 depends on DEBUG_KERNEL && KALLSYMS
1471 Normally kallsyms only contains the symbols of functions for nicer
1472 OOPS messages and backtraces (i.e., symbols from the text and inittext
1473 sections). This is sufficient for most cases. And only in very rare
1474 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1475 names of variables from the data sections, etc).
1477 This option makes sure that all symbols are loaded into the kernel
1478 image (i.e., symbols from all sections) in cost of increased kernel
1479 size (depending on the kernel configuration, it may be 300KiB or
1480 something like this).
1482 Say N unless you really need all symbols.
1486 bool "Enable support for printk" if EXPERT
1489 This option enables normal printk support. Removing it
1490 eliminates most of the message strings from the kernel image
1491 and makes the kernel more or less silent. As this makes it
1492 very difficult to diagnose system problems, saying N here is
1493 strongly discouraged.
1496 bool "BUG() support" if EXPERT
1499 Disabling this option eliminates support for BUG and WARN, reducing
1500 the size of your kernel image and potentially quietly ignoring
1501 numerous fatal conditions. You should only consider disabling this
1502 option for embedded systems with no facilities for reporting errors.
1508 bool "Enable ELF core dumps" if EXPERT
1510 Enable support for generating core dumps. Disabling saves about 4k.
1513 config PCSPKR_PLATFORM
1514 bool "Enable PC-Speaker support" if EXPERT
1515 depends on HAVE_PCSPKR_PLATFORM
1519 This option allows to disable the internal PC-Speaker
1520 support, saving some memory.
1524 bool "Enable full-sized data structures for core" if EXPERT
1526 Disabling this option reduces the size of miscellaneous core
1527 kernel data structures. This saves memory on small machines,
1528 but may reduce performance.
1531 bool "Enable futex support" if EXPERT
1535 Disabling this option will cause the kernel to be built without
1536 support for "fast userspace mutexes". The resulting kernel may not
1537 run glibc-based applications correctly.
1539 config HAVE_FUTEX_CMPXCHG
1543 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1544 is implemented and always working. This removes a couple of runtime
1548 bool "Enable eventpoll support" if EXPERT
1552 Disabling this option will cause the kernel to be built without
1553 support for epoll family of system calls.
1556 bool "Enable signalfd() system call" if EXPERT
1560 Enable the signalfd() system call that allows to receive signals
1561 on a file descriptor.
1566 bool "Enable timerfd() system call" if EXPERT
1570 Enable the timerfd() system call that allows to receive timer
1571 events on a file descriptor.
1576 bool "Enable eventfd() system call" if EXPERT
1580 Enable the eventfd() system call that allows to receive both
1581 kernel notification (ie. KAIO) or userspace notifications.
1585 # syscall, maps, verifier
1587 bool "Enable bpf() system call" if EXPERT
1592 Enable the bpf() system call that allows to manipulate eBPF
1593 programs and maps via file descriptors.
1596 bool "Use full shmem filesystem" if EXPERT
1600 The shmem is an internal filesystem used to manage shared memory.
1601 It is backed by swap and manages resource limits. It is also exported
1602 to userspace as tmpfs if TMPFS is enabled. Disabling this
1603 option replaces shmem and tmpfs with the much simpler ramfs code,
1604 which may be appropriate on small systems without swap.
1607 bool "Enable AIO support" if EXPERT
1610 This option enables POSIX asynchronous I/O which may by used
1611 by some high performance threaded applications. Disabling
1612 this option saves about 7k.
1614 config ADVISE_SYSCALLS
1615 bool "Enable madvise/fadvise syscalls" if EXPERT
1618 This option enables the madvise and fadvise syscalls, used by
1619 applications to advise the kernel about their future memory or file
1620 usage, improving performance. If building an embedded system where no
1621 applications use these syscalls, you can disable this option to save
1626 bool "Enable PCI quirk workarounds" if EXPERT
1629 This enables workarounds for various PCI chipset
1630 bugs/quirks. Disable this only if your target machine is
1631 unaffected by PCI quirks.
1634 bool "Embedded system"
1635 option allnoconfig_y
1638 This option should be enabled if compiling the kernel for
1639 an embedded system so certain expert options are available
1642 config HAVE_PERF_EVENTS
1645 See tools/perf/design.txt for details.
1647 config PERF_USE_VMALLOC
1650 See tools/perf/design.txt for details
1652 menu "Kernel Performance Events And Counters"
1655 bool "Kernel performance events and counters"
1656 default y if PROFILING
1657 depends on HAVE_PERF_EVENTS
1662 Enable kernel support for various performance events provided
1663 by software and hardware.
1665 Software events are supported either built-in or via the
1666 use of generic tracepoints.
1668 Most modern CPUs support performance events via performance
1669 counter registers. These registers count the number of certain
1670 types of hw events: such as instructions executed, cachemisses
1671 suffered, or branches mis-predicted - without slowing down the
1672 kernel or applications. These registers can also trigger interrupts
1673 when a threshold number of events have passed - and can thus be
1674 used to profile the code that runs on that CPU.
1676 The Linux Performance Event subsystem provides an abstraction of
1677 these software and hardware event capabilities, available via a
1678 system call and used by the "perf" utility in tools/perf/. It
1679 provides per task and per CPU counters, and it provides event
1680 capabilities on top of those.
1684 config DEBUG_PERF_USE_VMALLOC
1686 bool "Debug: use vmalloc to back perf mmap() buffers"
1687 depends on PERF_EVENTS && DEBUG_KERNEL
1688 select PERF_USE_VMALLOC
1690 Use vmalloc memory to back perf mmap() buffers.
1692 Mostly useful for debugging the vmalloc code on platforms
1693 that don't require it.
1699 config VM_EVENT_COUNTERS
1701 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1703 VM event counters are needed for event counts to be shown.
1704 This option allows the disabling of the VM event counters
1705 on EXPERT systems. /proc/vmstat will only show page counts
1706 if VM event counters are disabled.
1710 bool "Enable SLUB debugging support" if EXPERT
1711 depends on SLUB && SYSFS
1713 SLUB has extensive debug support features. Disabling these can
1714 result in significant savings in code size. This also disables
1715 SLUB sysfs support. /sys/slab will not exist and there will be
1716 no support for cache validation etc.
1719 bool "Disable heap randomization"
1722 Randomizing heap placement makes heap exploits harder, but it
1723 also breaks ancient binaries (including anything libc5 based).
1724 This option changes the bootup default to heap randomization
1725 disabled, and can be overridden at runtime by setting
1726 /proc/sys/kernel/randomize_va_space to 2.
1728 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1731 prompt "Choose SLAB allocator"
1734 This option allows to select a slab allocator.
1739 The regular slab allocator that is established and known to work
1740 well in all environments. It organizes cache hot objects in
1741 per cpu and per node queues.
1744 bool "SLUB (Unqueued Allocator)"
1746 SLUB is a slab allocator that minimizes cache line usage
1747 instead of managing queues of cached objects (SLAB approach).
1748 Per cpu caching is realized using slabs of objects instead
1749 of queues of objects. SLUB can use memory efficiently
1750 and has enhanced diagnostics. SLUB is the default choice for
1755 bool "SLOB (Simple Allocator)"
1757 SLOB replaces the stock allocator with a drastically simpler
1758 allocator. SLOB is generally more space efficient but
1759 does not perform as well on large systems.
1763 config SLUB_CPU_PARTIAL
1765 depends on SLUB && SMP
1766 bool "SLUB per cpu partial cache"
1768 Per cpu partial caches accellerate objects allocation and freeing
1769 that is local to a processor at the price of more indeterminism
1770 in the latency of the free. On overflow these caches will be cleared
1771 which requires the taking of locks that may cause latency spikes.
1772 Typically one would choose no for a realtime system.
1774 config MMAP_ALLOW_UNINITIALIZED
1775 bool "Allow mmapped anonymous memory to be uninitialized"
1776 depends on EXPERT && !MMU
1779 Normally, and according to the Linux spec, anonymous memory obtained
1780 from mmap() has it's contents cleared before it is passed to
1781 userspace. Enabling this config option allows you to request that
1782 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1783 providing a huge performance boost. If this option is not enabled,
1784 then the flag will be ignored.
1786 This is taken advantage of by uClibc's malloc(), and also by
1787 ELF-FDPIC binfmt's brk and stack allocator.
1789 Because of the obvious security issues, this option should only be
1790 enabled on embedded devices where you control what is run in
1791 userspace. Since that isn't generally a problem on no-MMU systems,
1792 it is normally safe to say Y here.
1794 See Documentation/nommu-mmap.txt for more information.
1796 config SYSTEM_TRUSTED_KEYRING
1797 bool "Provide system-wide ring of trusted keys"
1800 Provide a system keyring to which trusted keys can be added. Keys in
1801 the keyring are considered to be trusted. Keys may be added at will
1802 by the kernel from compiled-in data and from hardware key stores, but
1803 userspace may only add extra keys if those keys can be verified by
1804 keys already in the keyring.
1806 Keys in this keyring are used by module signature checking.
1809 bool "Profiling support"
1811 Say Y here to enable the extended profiling support mechanisms used
1812 by profilers such as OProfile.
1815 # Place an empty function call at each tracepoint site. Can be
1816 # dynamically changed for a probe function.
1821 source "arch/Kconfig"
1823 endmenu # General setup
1825 config HAVE_GENERIC_DMA_COHERENT
1832 depends on SLAB || SLUB_DEBUG
1840 default 0 if BASE_FULL
1841 default 1 if !BASE_FULL
1844 bool "Enable loadable module support"
1847 Kernel modules are small pieces of compiled code which can
1848 be inserted in the running kernel, rather than being
1849 permanently built into the kernel. You use the "modprobe"
1850 tool to add (and sometimes remove) them. If you say Y here,
1851 many parts of the kernel can be built as modules (by
1852 answering M instead of Y where indicated): this is most
1853 useful for infrequently used options which are not required
1854 for booting. For more information, see the man pages for
1855 modprobe, lsmod, modinfo, insmod and rmmod.
1857 If you say Y here, you will need to run "make
1858 modules_install" to put the modules under /lib/modules/
1859 where modprobe can find them (you may need to be root to do
1866 config MODULE_FORCE_LOAD
1867 bool "Forced module loading"
1870 Allow loading of modules without version information (ie. modprobe
1871 --force). Forced module loading sets the 'F' (forced) taint flag and
1872 is usually a really bad idea.
1874 config MODULE_UNLOAD
1875 bool "Module unloading"
1877 Without this option you will not be able to unload any
1878 modules (note that some modules may not be unloadable
1879 anyway), which makes your kernel smaller, faster
1880 and simpler. If unsure, say Y.
1882 config MODULE_FORCE_UNLOAD
1883 bool "Forced module unloading"
1884 depends on MODULE_UNLOAD
1886 This option allows you to force a module to unload, even if the
1887 kernel believes it is unsafe: the kernel will remove the module
1888 without waiting for anyone to stop using it (using the -f option to
1889 rmmod). This is mainly for kernel developers and desperate users.
1893 bool "Module versioning support"
1894 # LTO should work with gcc 4.9
1897 Usually, you have to use modules compiled with your kernel.
1898 Saying Y here makes it sometimes possible to use modules
1899 compiled for different kernels, by adding enough information
1900 to the modules to (hopefully) spot any changes which would
1901 make them incompatible with the kernel you are running. If
1904 config MODULE_SRCVERSION_ALL
1905 bool "Source checksum for all modules"
1907 Modules which contain a MODULE_VERSION get an extra "srcversion"
1908 field inserted into their modinfo section, which contains a
1909 sum of the source files which made it. This helps maintainers
1910 see exactly which source was used to build a module (since
1911 others sometimes change the module source without updating
1912 the version). With this option, such a "srcversion" field
1913 will be created for all modules. If unsure, say N.
1916 bool "Module signature verification"
1918 select SYSTEM_TRUSTED_KEYRING
1921 select ASYMMETRIC_KEY_TYPE
1922 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1923 select PUBLIC_KEY_ALGO_RSA
1926 select X509_CERTIFICATE_PARSER
1928 Check modules for valid signatures upon load: the signature
1929 is simply appended to the module. For more information see
1930 Documentation/module-signing.txt.
1932 !!!WARNING!!! If you enable this option, you MUST make sure that the
1933 module DOES NOT get stripped after being signed. This includes the
1934 debuginfo strip done by some packagers (such as rpmbuild) and
1935 inclusion into an initramfs that wants the module size reduced.
1937 config MODULE_SIG_FORCE
1938 bool "Require modules to be validly signed"
1939 depends on MODULE_SIG
1941 Reject unsigned modules or signed modules for which we don't have a
1942 key. Without this, such modules will simply taint the kernel.
1944 config MODULE_SIG_ALL
1945 bool "Automatically sign all modules"
1947 depends on MODULE_SIG
1949 Sign all modules during make modules_install. Without this option,
1950 modules must be signed manually, using the scripts/sign-file tool.
1952 comment "Do not forget to sign required modules with scripts/sign-file"
1953 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1956 prompt "Which hash algorithm should modules be signed with?"
1957 depends on MODULE_SIG
1959 This determines which sort of hashing algorithm will be used during
1960 signature generation. This algorithm _must_ be built into the kernel
1961 directly so that signature verification can take place. It is not
1962 possible to load a signed module containing the algorithm to check
1963 the signature on that module.
1965 config MODULE_SIG_SHA1
1966 bool "Sign modules with SHA-1"
1969 config MODULE_SIG_SHA224
1970 bool "Sign modules with SHA-224"
1971 select CRYPTO_SHA256
1973 config MODULE_SIG_SHA256
1974 bool "Sign modules with SHA-256"
1975 select CRYPTO_SHA256
1977 config MODULE_SIG_SHA384
1978 bool "Sign modules with SHA-384"
1979 select CRYPTO_SHA512
1981 config MODULE_SIG_SHA512
1982 bool "Sign modules with SHA-512"
1983 select CRYPTO_SHA512
1987 config MODULE_SIG_HASH
1989 depends on MODULE_SIG
1990 default "sha1" if MODULE_SIG_SHA1
1991 default "sha224" if MODULE_SIG_SHA224
1992 default "sha256" if MODULE_SIG_SHA256
1993 default "sha384" if MODULE_SIG_SHA384
1994 default "sha512" if MODULE_SIG_SHA512
1996 config MODULE_COMPRESS
1997 bool "Compress modules on installation"
2000 This option compresses the kernel modules when 'make
2001 modules_install' is run.
2003 The modules will be compressed either using gzip or xz depend on the
2004 choice made in "Compression algorithm".
2006 module-init-tools has support for gzip format while kmod handle gzip
2007 and xz compressed modules.
2009 When a kernel module is installed from outside of the main kernel
2010 source and uses the Kbuild system for installing modules then that
2011 kernel module will also be compressed when it is installed.
2013 This option provides little benefit when the modules are to be used inside
2014 an initrd or initramfs, it generally is more efficient to compress the whole
2015 initrd or initramfs instead.
2017 This is fully compatible with signed modules while the signed module is
2018 compressed. module-init-tools or kmod handles decompression and provide to
2019 other layer the uncompressed but signed payload.
2022 prompt "Compression algorithm"
2023 depends on MODULE_COMPRESS
2024 default MODULE_COMPRESS_GZIP
2026 This determines which sort of compression will be used during
2027 'make modules_install'.
2029 GZIP (default) and XZ are supported.
2031 config MODULE_COMPRESS_GZIP
2034 config MODULE_COMPRESS_XZ
2041 config INIT_ALL_POSSIBLE
2044 Back when each arch used to define their own cpu_online_mask and
2045 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2046 with all 1s, and others with all 0s. When they were centralised,
2047 it was better to provide this option than to break all the archs
2048 and have several arch maintainers pursuing me down dark alleys.
2053 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
2055 Need stop_machine() primitive.
2057 source "block/Kconfig"
2059 config PREEMPT_NOTIFIERS
2066 # Can be selected by architectures with broken toolchains
2067 # that get confused by correct const<->read_only section
2069 config BROKEN_RODATA
2075 Build a simple ASN.1 grammar compiler that produces a bytecode output
2076 that can be interpreted by the ASN.1 stream decoder and used to
2077 inform it as to what tags are to be expected in a stream and what
2078 functions to call on what tags.
2080 source "kernel/Kconfig.locks"
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