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"
399 If you say Y here, a user level program will be able to instruct the
400 kernel (via a special system call) to write process accounting
401 information to a file: whenever a process exits, information about
402 that process will be appended to the file by the kernel. The
403 information includes things such as creation time, owning user,
404 command name, memory usage, controlling terminal etc. (the complete
405 list is in the struct acct in <file:include/linux/acct.h>). It is
406 up to the user level program to do useful things with this
407 information. This is generally a good idea, so say Y.
409 config BSD_PROCESS_ACCT_V3
410 bool "BSD Process Accounting version 3 file format"
411 depends on BSD_PROCESS_ACCT
414 If you say Y here, the process accounting information is written
415 in a new file format that also logs the process IDs of each
416 process and it's parent. Note that this file format is incompatible
417 with previous v0/v1/v2 file formats, so you will need updated tools
418 for processing it. A preliminary version of these tools is available
419 at <http://www.gnu.org/software/acct/>.
422 bool "Export task/process statistics through netlink"
427 Export selected statistics for tasks/processes through the
428 generic netlink interface. Unlike BSD process accounting, the
429 statistics are available during the lifetime of tasks/processes as
430 responses to commands. Like BSD accounting, they are sent to user
435 config TASK_DELAY_ACCT
436 bool "Enable per-task delay accounting"
439 Collect information on time spent by a task waiting for system
440 resources like cpu, synchronous block I/O completion and swapping
441 in pages. Such statistics can help in setting a task's priorities
442 relative to other tasks for cpu, io, rss limits etc.
447 bool "Enable extended accounting over taskstats"
450 Collect extended task accounting data and send the data
451 to userland for processing over the taskstats interface.
455 config TASK_IO_ACCOUNTING
456 bool "Enable per-task storage I/O accounting"
457 depends on TASK_XACCT
459 Collect information on the number of bytes of storage I/O which this
464 endmenu # "CPU/Task time and stats accounting"
469 prompt "RCU Implementation"
473 bool "Tree-based hierarchical RCU"
474 depends on !PREEMPT && SMP
476 This option selects the RCU implementation that is
477 designed for very large SMP system with hundreds or
478 thousands of CPUs. It also scales down nicely to
482 bool "Preemptible tree-based hierarchical RCU"
485 This option selects the RCU implementation that is
486 designed for very large SMP systems with hundreds or
487 thousands of CPUs, but for which real-time response
488 is also required. It also scales down nicely to
491 Select this option if you are unsure.
494 bool "UP-only small-memory-footprint RCU"
495 depends on !PREEMPT && !SMP
497 This option selects the RCU implementation that is
498 designed for UP systems from which real-time response
499 is not required. This option greatly reduces the
500 memory footprint of RCU.
507 This option selects the sleepable version of RCU. This version
508 permits arbitrary sleeping or blocking within RCU read-side critical
516 This option enables a task-based RCU implementation that uses
517 only voluntary context switch (not preemption!), idle, and
518 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
534 This option sets hooks on kernel / userspace boundaries and
535 puts RCU in extended quiescent state when the CPU runs in
536 userspace. It means that when a CPU runs in userspace, it is
537 excluded from the global RCU state machine and thus doesn't
538 try to keep the timer tick on for RCU.
540 config CONTEXT_TRACKING_FORCE
541 bool "Force context tracking"
542 depends on CONTEXT_TRACKING
543 default y if !NO_HZ_FULL
545 The major pre-requirement for full dynticks to work is to
546 support the context tracking subsystem. But there are also
547 other dependencies to provide in order to make the full
550 This option stands for testing when an arch implements the
551 context tracking backend but doesn't yet fullfill all the
552 requirements to make the full dynticks feature working.
553 Without the full dynticks, there is no way to test the support
554 for context tracking and the subsystems that rely on it: RCU
555 userspace extended quiescent state and tickless cputime
556 accounting. This option copes with the absence of the full
557 dynticks subsystem by forcing the context tracking on all
560 Say Y only if you're working on the development of an
561 architecture backend for the context tracking.
563 Say N otherwise, this option brings an overhead that you
564 don't want in production.
568 int "Tree-based hierarchical RCU fanout value"
571 depends on TREE_RCU || PREEMPT_RCU
575 This option controls the fanout of hierarchical implementations
576 of RCU, allowing RCU to work efficiently on machines with
577 large numbers of CPUs. This value must be at least the fourth
578 root of NR_CPUS, which allows NR_CPUS to be insanely large.
579 The default value of RCU_FANOUT should be used for production
580 systems, but if you are stress-testing the RCU implementation
581 itself, small RCU_FANOUT values allow you to test large-system
582 code paths on small(er) systems.
584 Select a specific number if testing RCU itself.
585 Take the default if unsure.
587 config RCU_FANOUT_LEAF
588 int "Tree-based hierarchical RCU leaf-level fanout value"
589 range 2 RCU_FANOUT if 64BIT
590 range 2 RCU_FANOUT if !64BIT
591 depends on TREE_RCU || PREEMPT_RCU
594 This option controls the leaf-level fanout of hierarchical
595 implementations of RCU, and allows trading off cache misses
596 against lock contention. Systems that synchronize their
597 scheduling-clock interrupts for energy-efficiency reasons will
598 want the default because the smaller leaf-level fanout keeps
599 lock contention levels acceptably low. Very large systems
600 (hundreds or thousands of CPUs) will instead want to set this
601 value to the maximum value possible in order to reduce the
602 number of cache misses incurred during RCU's grace-period
603 initialization. These systems tend to run CPU-bound, and thus
604 are not helped by synchronized interrupts, and thus tend to
605 skew them, which reduces lock contention enough that large
606 leaf-level fanouts work well.
608 Select a specific number if testing RCU itself.
610 Select the maximum permissible value for large systems.
612 Take the default if unsure.
614 config RCU_FANOUT_EXACT
615 bool "Disable tree-based hierarchical RCU auto-balancing"
616 depends on TREE_RCU || PREEMPT_RCU
619 This option forces use of the exact RCU_FANOUT value specified,
620 regardless of imbalances in the hierarchy. This is useful for
621 testing RCU itself, and might one day be useful on systems with
622 strong NUMA behavior.
624 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
628 config RCU_FAST_NO_HZ
629 bool "Accelerate last non-dyntick-idle CPU's grace periods"
630 depends on NO_HZ_COMMON && SMP
633 This option permits CPUs to enter dynticks-idle state even if
634 they have RCU callbacks queued, and prevents RCU from waking
635 these CPUs up more than roughly once every four jiffies (by
636 default, you can adjust this using the rcutree.rcu_idle_gp_delay
637 parameter), thus improving energy efficiency. On the other
638 hand, this option increases the duration of RCU grace periods,
639 for example, slowing down synchronize_rcu().
641 Say Y if energy efficiency is critically important, and you
642 don't care about increased grace-period durations.
644 Say N if you are unsure.
646 config TREE_RCU_TRACE
647 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
650 This option provides tracing for the TREE_RCU and
651 PREEMPT_RCU implementations, permitting Makefile to
652 trivially select kernel/rcutree_trace.c.
655 bool "Enable RCU priority boosting"
656 depends on RT_MUTEXES && PREEMPT_RCU
659 This option boosts the priority of preempted RCU readers that
660 block the current preemptible RCU grace period for too long.
661 This option also prevents heavy loads from blocking RCU
662 callback invocation for all flavors of RCU.
664 Say Y here if you are working with real-time apps or heavy loads
665 Say N here if you are unsure.
667 config RCU_KTHREAD_PRIO
668 int "Real-time priority to use for RCU worker threads"
669 range 1 99 if RCU_BOOST
670 range 0 99 if !RCU_BOOST
671 default 1 if RCU_BOOST
672 default 0 if !RCU_BOOST
674 This option specifies the SCHED_FIFO priority value that will be
675 assigned to the rcuc/n and rcub/n threads and is also the value
676 used for RCU_BOOST (if enabled). If you are working with a
677 real-time application that has one or more CPU-bound threads
678 running at a real-time priority level, you should set
679 RCU_KTHREAD_PRIO to a priority higher than the highest-priority
680 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
681 value of 1 is appropriate in the common case, which is real-time
682 applications that do not have any CPU-bound threads.
684 Some real-time applications might not have a single real-time
685 thread that saturates a given CPU, but instead might have
686 multiple real-time threads that, taken together, fully utilize
687 that CPU. In this case, you should set RCU_KTHREAD_PRIO to
688 a priority higher than the lowest-priority thread that is
689 conspiring to prevent the CPU from running any non-real-time
690 tasks. For example, if one thread at priority 10 and another
691 thread at priority 5 are between themselves fully consuming
692 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
693 set to priority 6 or higher.
695 Specify the real-time priority, or take the default if unsure.
697 config RCU_BOOST_DELAY
698 int "Milliseconds to delay boosting after RCU grace-period start"
703 This option specifies the time to wait after the beginning of
704 a given grace period before priority-boosting preempted RCU
705 readers blocking that grace period. Note that any RCU reader
706 blocking an expedited RCU grace period is boosted immediately.
708 Accept the default if unsure.
711 bool "Offload RCU callback processing from boot-selected CPUs"
712 depends on TREE_RCU || PREEMPT_RCU
715 Use this option to reduce OS jitter for aggressive HPC or
716 real-time workloads. It can also be used to offload RCU
717 callback invocation to energy-efficient CPUs in battery-powered
718 asymmetric multiprocessors.
720 This option offloads callback invocation from the set of
721 CPUs specified at boot time by the rcu_nocbs parameter.
722 For each such CPU, a kthread ("rcuox/N") will be created to
723 invoke callbacks, where the "N" is the CPU being offloaded,
724 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
725 "s" for RCU-sched. Nothing prevents this kthread from running
726 on the specified CPUs, but (1) the kthreads may be preempted
727 between each callback, and (2) affinity or cgroups can be used
728 to force the kthreads to run on whatever set of CPUs is desired.
730 Say Y here if you want to help to debug reduced OS jitter.
731 Say N here if you are unsure.
734 prompt "Build-forced no-CBs CPUs"
735 default RCU_NOCB_CPU_NONE
736 depends on RCU_NOCB_CPU
738 This option allows no-CBs CPUs (whose RCU callbacks are invoked
739 from kthreads rather than from softirq context) to be specified
740 at build time. Additional no-CBs CPUs may be specified by
741 the rcu_nocbs= boot parameter.
743 config RCU_NOCB_CPU_NONE
744 bool "No build_forced no-CBs CPUs"
746 This option does not force any of the CPUs to be no-CBs CPUs.
747 Only CPUs designated by the rcu_nocbs= boot parameter will be
748 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
749 kthreads whose names begin with "rcuo". All other CPUs will
750 invoke their own RCU callbacks in softirq context.
752 Select this option if you want to choose no-CBs CPUs at
753 boot time, for example, to allow testing of different no-CBs
754 configurations without having to rebuild the kernel each time.
756 config RCU_NOCB_CPU_ZERO
757 bool "CPU 0 is a build_forced no-CBs CPU"
759 This option forces CPU 0 to be a no-CBs CPU, so that its RCU
760 callbacks are invoked by a per-CPU kthread whose name begins
761 with "rcuo". Additional CPUs may be designated as no-CBs
762 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
763 All other CPUs will invoke their own RCU callbacks in softirq
766 Select this if CPU 0 needs to be a no-CBs CPU for real-time
767 or energy-efficiency reasons, but the real reason it exists
768 is to ensure that randconfig testing covers mixed systems.
770 config RCU_NOCB_CPU_ALL
771 bool "All CPUs are build_forced no-CBs CPUs"
773 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
774 boot parameter will be ignored. All CPUs' RCU callbacks will
775 be executed in the context of per-CPU rcuo kthreads created for
776 this purpose. Assuming that the kthreads whose names start with
777 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
778 on the remaining CPUs, but might decrease memory locality during
779 RCU-callback invocation, thus potentially degrading throughput.
781 Select this if all CPUs need to be no-CBs CPUs for real-time
782 or energy-efficiency reasons.
786 config RCU_EXPEDITE_BOOT
790 This option enables expedited grace periods at boot time,
791 as if rcu_expedite_gp() had been invoked early in boot.
792 The corresponding rcu_unexpedite_gp() is invoked from
793 rcu_end_inkernel_boot(), which is intended to be invoked
794 at the end of the kernel-only boot sequence, just before
797 Accept the default if unsure.
799 endmenu # "RCU Subsystem"
806 tristate "Kernel .config support"
809 This option enables the complete Linux kernel ".config" file
810 contents to be saved in the kernel. It provides documentation
811 of which kernel options are used in a running kernel or in an
812 on-disk kernel. This information can be extracted from the kernel
813 image file with the script scripts/extract-ikconfig and used as
814 input to rebuild the current kernel or to build another kernel.
815 It can also be extracted from a running kernel by reading
816 /proc/config.gz if enabled (below).
819 bool "Enable access to .config through /proc/config.gz"
820 depends on IKCONFIG && PROC_FS
822 This option enables access to the kernel configuration file
823 through /proc/config.gz.
826 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
831 Select the minimal kernel log buffer size as a power of 2.
832 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
833 parameter, see below. Any higher size also might be forced
834 by "log_buf_len" boot parameter.
844 config LOG_CPU_MAX_BUF_SHIFT
845 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
848 default 12 if !BASE_SMALL
849 default 0 if BASE_SMALL
852 This option allows to increase the default ring buffer size
853 according to the number of CPUs. The value defines the contribution
854 of each CPU as a power of 2. The used space is typically only few
855 lines however it might be much more when problems are reported,
858 The increased size means that a new buffer has to be allocated and
859 the original static one is unused. It makes sense only on systems
860 with more CPUs. Therefore this value is used only when the sum of
861 contributions is greater than the half of the default kernel ring
862 buffer as defined by LOG_BUF_SHIFT. The default values are set
863 so that more than 64 CPUs are needed to trigger the allocation.
865 Also this option is ignored when "log_buf_len" kernel parameter is
866 used as it forces an exact (power of two) size of the ring buffer.
868 The number of possible CPUs is used for this computation ignoring
869 hotplugging making the compuation optimal for the the worst case
870 scenerio while allowing a simple algorithm to be used from bootup.
872 Examples shift values and their meaning:
873 17 => 128 KB for each CPU
874 16 => 64 KB for each CPU
875 15 => 32 KB for each CPU
876 14 => 16 KB for each CPU
877 13 => 8 KB for each CPU
878 12 => 4 KB for each CPU
881 # Architectures with an unreliable sched_clock() should select this:
883 config HAVE_UNSTABLE_SCHED_CLOCK
886 config GENERIC_SCHED_CLOCK
890 # For architectures that want to enable the support for NUMA-affine scheduler
893 config ARCH_SUPPORTS_NUMA_BALANCING
897 # For architectures that know their GCC __int128 support is sound
899 config ARCH_SUPPORTS_INT128
902 # For architectures that (ab)use NUMA to represent different memory regions
903 # all cpu-local but of different latencies, such as SuperH.
905 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
908 config NUMA_BALANCING
909 bool "Memory placement aware NUMA scheduler"
910 depends on ARCH_SUPPORTS_NUMA_BALANCING
911 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
912 depends on SMP && NUMA && MIGRATION
914 This option adds support for automatic NUMA aware memory/task placement.
915 The mechanism is quite primitive and is based on migrating memory when
916 it has references to the node the task is running on.
918 This system will be inactive on UMA systems.
920 config NUMA_BALANCING_DEFAULT_ENABLED
921 bool "Automatically enable NUMA aware memory/task placement"
923 depends on NUMA_BALANCING
925 If set, automatic NUMA balancing will be enabled if running on a NUMA
929 bool "Control Group support"
932 This option adds support for grouping sets of processes together, for
933 use with process control subsystems such as Cpusets, CFS, memory
934 controls or device isolation.
936 - Documentation/scheduler/sched-design-CFS.txt (CFS)
937 - Documentation/cgroups/ (features for grouping, isolation
938 and resource control)
945 bool "Example debug cgroup subsystem"
948 This option enables a simple cgroup subsystem that
949 exports useful debugging information about the cgroups
954 config CGROUP_FREEZER
955 bool "Freezer cgroup subsystem"
957 Provides a way to freeze and unfreeze all tasks in a
961 bool "Device controller for cgroups"
963 Provides a cgroup implementing whitelists for devices which
964 a process in the cgroup can mknod or open.
967 bool "Cpuset support"
969 This option will let you create and manage CPUSETs which
970 allow dynamically partitioning a system into sets of CPUs and
971 Memory Nodes and assigning tasks to run only within those sets.
972 This is primarily useful on large SMP or NUMA systems.
976 config PROC_PID_CPUSET
977 bool "Include legacy /proc/<pid>/cpuset file"
981 config CGROUP_CPUACCT
982 bool "Simple CPU accounting cgroup subsystem"
984 Provides a simple Resource Controller for monitoring the
985 total CPU consumed by the tasks in a cgroup.
991 bool "Memory Resource Controller for Control Groups"
995 Provides a memory resource controller that manages both anonymous
996 memory and page cache. (See Documentation/cgroups/memory.txt)
999 bool "Memory Resource Controller Swap Extension"
1000 depends on MEMCG && SWAP
1002 Add swap management feature to memory resource controller. When you
1003 enable this, you can limit mem+swap usage per cgroup. In other words,
1004 when you disable this, memory resource controller has no cares to
1005 usage of swap...a process can exhaust all of the swap. This extension
1006 is useful when you want to avoid exhaustion swap but this itself
1007 adds more overheads and consumes memory for remembering information.
1008 Especially if you use 32bit system or small memory system, please
1009 be careful about enabling this. When memory resource controller
1010 is disabled by boot option, this will be automatically disabled and
1011 there will be no overhead from this. Even when you set this config=y,
1012 if boot option "swapaccount=0" is set, swap will not be accounted.
1013 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1014 size is 4096bytes, 512k per 1Gbytes of swap.
1015 config MEMCG_SWAP_ENABLED
1016 bool "Memory Resource Controller Swap Extension enabled by default"
1017 depends on MEMCG_SWAP
1020 Memory Resource Controller Swap Extension comes with its price in
1021 a bigger memory consumption. General purpose distribution kernels
1022 which want to enable the feature but keep it disabled by default
1023 and let the user enable it by swapaccount=1 boot command line
1024 parameter should have this option unselected.
1025 For those who want to have the feature enabled by default should
1026 select this option (if, for some reason, they need to disable it
1027 then swapaccount=0 does the trick).
1029 bool "Memory Resource Controller Kernel Memory accounting"
1031 depends on SLUB || SLAB
1033 The Kernel Memory extension for Memory Resource Controller can limit
1034 the amount of memory used by kernel objects in the system. Those are
1035 fundamentally different from the entities handled by the standard
1036 Memory Controller, which are page-based, and can be swapped. Users of
1037 the kmem extension can use it to guarantee that no group of processes
1038 will ever exhaust kernel resources alone.
1040 config CGROUP_HUGETLB
1041 bool "HugeTLB Resource Controller for Control Groups"
1042 depends on HUGETLB_PAGE
1046 Provides a cgroup Resource Controller for HugeTLB pages.
1047 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1048 The limit is enforced during page fault. Since HugeTLB doesn't
1049 support page reclaim, enforcing the limit at page fault time implies
1050 that, the application will get SIGBUS signal if it tries to access
1051 HugeTLB pages beyond its limit. This requires the application to know
1052 beforehand how much HugeTLB pages it would require for its use. The
1053 control group is tracked in the third page lru pointer. This means
1054 that we cannot use the controller with huge page less than 3 pages.
1057 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1058 depends on PERF_EVENTS && CGROUPS
1060 This option extends the per-cpu mode to restrict monitoring to
1061 threads which belong to the cgroup specified and run on the
1066 menuconfig CGROUP_SCHED
1067 bool "Group CPU scheduler"
1070 This feature lets CPU scheduler recognize task groups and control CPU
1071 bandwidth allocation to such task groups. It uses cgroups to group
1075 config FAIR_GROUP_SCHED
1076 bool "Group scheduling for SCHED_OTHER"
1077 depends on CGROUP_SCHED
1078 default CGROUP_SCHED
1080 config CFS_BANDWIDTH
1081 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1082 depends on FAIR_GROUP_SCHED
1085 This option allows users to define CPU bandwidth rates (limits) for
1086 tasks running within the fair group scheduler. Groups with no limit
1087 set are considered to be unconstrained and will run with no
1089 See tip/Documentation/scheduler/sched-bwc.txt for more information.
1091 config RT_GROUP_SCHED
1092 bool "Group scheduling for SCHED_RR/FIFO"
1093 depends on CGROUP_SCHED
1096 This feature lets you explicitly allocate real CPU bandwidth
1097 to task groups. If enabled, it will also make it impossible to
1098 schedule realtime tasks for non-root users until you allocate
1099 realtime bandwidth for them.
1100 See Documentation/scheduler/sched-rt-group.txt for more information.
1105 bool "Block IO controller"
1109 Generic block IO controller cgroup interface. This is the common
1110 cgroup interface which should be used by various IO controlling
1113 Currently, CFQ IO scheduler uses it to recognize task groups and
1114 control disk bandwidth allocation (proportional time slice allocation)
1115 to such task groups. It is also used by bio throttling logic in
1116 block layer to implement upper limit in IO rates on a device.
1118 This option only enables generic Block IO controller infrastructure.
1119 One needs to also enable actual IO controlling logic/policy. For
1120 enabling proportional weight division of disk bandwidth in CFQ, set
1121 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1122 CONFIG_BLK_DEV_THROTTLING=y.
1124 See Documentation/cgroups/blkio-controller.txt for more information.
1126 config DEBUG_BLK_CGROUP
1127 bool "Enable Block IO controller debugging"
1128 depends on BLK_CGROUP
1131 Enable some debugging help. Currently it exports additional stat
1132 files in a cgroup which can be useful for debugging.
1136 config CHECKPOINT_RESTORE
1137 bool "Checkpoint/restore support" if EXPERT
1140 Enables additional kernel features in a sake of checkpoint/restore.
1141 In particular it adds auxiliary prctl codes to setup process text,
1142 data and heap segment sizes, and a few additional /proc filesystem
1145 If unsure, say N here.
1147 menuconfig NAMESPACES
1148 bool "Namespaces support" if EXPERT
1149 depends on MULTIUSER
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.
1307 config SYSCTL_EXCEPTION_TRACE
1310 Enable support for /proc/sys/debug/exception-trace.
1312 config SYSCTL_ARCH_UNALIGN_NO_WARN
1315 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1316 Allows arch to define/use @no_unaligned_warning to possibly warn
1317 about unaligned access emulation going on under the hood.
1319 config SYSCTL_ARCH_UNALIGN_ALLOW
1322 Enable support for /proc/sys/kernel/unaligned-trap
1323 Allows arches to define/use @unaligned_enabled to runtime toggle
1324 the unaligned access emulation.
1325 see arch/parisc/kernel/unaligned.c for reference
1327 config HAVE_PCSPKR_PLATFORM
1330 # interpreter that classic socket filters depend on
1335 bool "Configure standard kernel features (expert users)"
1336 # Unhide debug options, to make the on-by-default options visible
1339 This option allows certain base kernel options and settings
1340 to be disabled or tweaked. This is for specialized
1341 environments which can tolerate a "non-standard" kernel.
1342 Only use this if you really know what you are doing.
1345 bool "Enable 16-bit UID system calls" if EXPERT
1346 depends on HAVE_UID16 && MULTIUSER
1349 This enables the legacy 16-bit UID syscall wrappers.
1352 bool "Multiple users, groups and capabilities support" if EXPERT
1355 This option enables support for non-root users, groups and
1358 If you say N here, all processes will run with UID 0, GID 0, and all
1359 possible capabilities. Saying N here also compiles out support for
1360 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1363 If unsure, say Y here.
1365 config SGETMASK_SYSCALL
1366 bool "sgetmask/ssetmask syscalls support" if EXPERT
1367 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1369 sys_sgetmask and sys_ssetmask are obsolete system calls
1370 no longer supported in libc but still enabled by default in some
1373 If unsure, leave the default option here.
1375 config SYSFS_SYSCALL
1376 bool "Sysfs syscall support" if EXPERT
1379 sys_sysfs is an obsolete system call no longer supported in libc.
1380 Note that disabling this option is more secure but might break
1381 compatibility with some systems.
1383 If unsure say Y here.
1385 config SYSCTL_SYSCALL
1386 bool "Sysctl syscall support" if EXPERT
1387 depends on PROC_SYSCTL
1391 sys_sysctl uses binary paths that have been found challenging
1392 to properly maintain and use. The interface in /proc/sys
1393 using paths with ascii names is now the primary path to this
1396 Almost nothing using the binary sysctl interface so if you are
1397 trying to save some space it is probably safe to disable this,
1398 making your kernel marginally smaller.
1400 If unsure say N here.
1403 bool "Load all symbols for debugging/ksymoops" if EXPERT
1406 Say Y here to let the kernel print out symbolic crash information and
1407 symbolic stack backtraces. This increases the size of the kernel
1408 somewhat, as all symbols have to be loaded into the kernel image.
1411 bool "Include all symbols in kallsyms"
1412 depends on DEBUG_KERNEL && KALLSYMS
1414 Normally kallsyms only contains the symbols of functions for nicer
1415 OOPS messages and backtraces (i.e., symbols from the text and inittext
1416 sections). This is sufficient for most cases. And only in very rare
1417 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1418 names of variables from the data sections, etc).
1420 This option makes sure that all symbols are loaded into the kernel
1421 image (i.e., symbols from all sections) in cost of increased kernel
1422 size (depending on the kernel configuration, it may be 300KiB or
1423 something like this).
1425 Say N unless you really need all symbols.
1429 bool "Enable support for printk" if EXPERT
1432 This option enables normal printk support. Removing it
1433 eliminates most of the message strings from the kernel image
1434 and makes the kernel more or less silent. As this makes it
1435 very difficult to diagnose system problems, saying N here is
1436 strongly discouraged.
1439 bool "BUG() support" if EXPERT
1442 Disabling this option eliminates support for BUG and WARN, reducing
1443 the size of your kernel image and potentially quietly ignoring
1444 numerous fatal conditions. You should only consider disabling this
1445 option for embedded systems with no facilities for reporting errors.
1451 bool "Enable ELF core dumps" if EXPERT
1453 Enable support for generating core dumps. Disabling saves about 4k.
1456 config PCSPKR_PLATFORM
1457 bool "Enable PC-Speaker support" if EXPERT
1458 depends on HAVE_PCSPKR_PLATFORM
1462 This option allows to disable the internal PC-Speaker
1463 support, saving some memory.
1467 bool "Enable full-sized data structures for core" if EXPERT
1469 Disabling this option reduces the size of miscellaneous core
1470 kernel data structures. This saves memory on small machines,
1471 but may reduce performance.
1474 bool "Enable futex support" if EXPERT
1478 Disabling this option will cause the kernel to be built without
1479 support for "fast userspace mutexes". The resulting kernel may not
1480 run glibc-based applications correctly.
1482 config HAVE_FUTEX_CMPXCHG
1486 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1487 is implemented and always working. This removes a couple of runtime
1491 bool "Enable eventpoll support" if EXPERT
1495 Disabling this option will cause the kernel to be built without
1496 support for epoll family of system calls.
1499 bool "Enable signalfd() system call" if EXPERT
1503 Enable the signalfd() system call that allows to receive signals
1504 on a file descriptor.
1509 bool "Enable timerfd() system call" if EXPERT
1513 Enable the timerfd() system call that allows to receive timer
1514 events on a file descriptor.
1519 bool "Enable eventfd() system call" if EXPERT
1523 Enable the eventfd() system call that allows to receive both
1524 kernel notification (ie. KAIO) or userspace notifications.
1528 # syscall, maps, verifier
1530 bool "Enable bpf() system call"
1535 Enable the bpf() system call that allows to manipulate eBPF
1536 programs and maps via file descriptors.
1539 bool "Use full shmem filesystem" if EXPERT
1543 The shmem is an internal filesystem used to manage shared memory.
1544 It is backed by swap and manages resource limits. It is also exported
1545 to userspace as tmpfs if TMPFS is enabled. Disabling this
1546 option replaces shmem and tmpfs with the much simpler ramfs code,
1547 which may be appropriate on small systems without swap.
1550 bool "Enable AIO support" if EXPERT
1553 This option enables POSIX asynchronous I/O which may by used
1554 by some high performance threaded applications. Disabling
1555 this option saves about 7k.
1557 config ADVISE_SYSCALLS
1558 bool "Enable madvise/fadvise syscalls" if EXPERT
1561 This option enables the madvise and fadvise syscalls, used by
1562 applications to advise the kernel about their future memory or file
1563 usage, improving performance. If building an embedded system where no
1564 applications use these syscalls, you can disable this option to save
1569 bool "Enable PCI quirk workarounds" if EXPERT
1572 This enables workarounds for various PCI chipset
1573 bugs/quirks. Disable this only if your target machine is
1574 unaffected by PCI quirks.
1577 bool "Embedded system"
1578 option allnoconfig_y
1581 This option should be enabled if compiling the kernel for
1582 an embedded system so certain expert options are available
1585 config HAVE_PERF_EVENTS
1588 See tools/perf/design.txt for details.
1590 config PERF_USE_VMALLOC
1593 See tools/perf/design.txt for details
1595 menu "Kernel Performance Events And Counters"
1598 bool "Kernel performance events and counters"
1599 default y if PROFILING
1600 depends on HAVE_PERF_EVENTS
1605 Enable kernel support for various performance events provided
1606 by software and hardware.
1608 Software events are supported either built-in or via the
1609 use of generic tracepoints.
1611 Most modern CPUs support performance events via performance
1612 counter registers. These registers count the number of certain
1613 types of hw events: such as instructions executed, cachemisses
1614 suffered, or branches mis-predicted - without slowing down the
1615 kernel or applications. These registers can also trigger interrupts
1616 when a threshold number of events have passed - and can thus be
1617 used to profile the code that runs on that CPU.
1619 The Linux Performance Event subsystem provides an abstraction of
1620 these software and hardware event capabilities, available via a
1621 system call and used by the "perf" utility in tools/perf/. It
1622 provides per task and per CPU counters, and it provides event
1623 capabilities on top of those.
1627 config DEBUG_PERF_USE_VMALLOC
1629 bool "Debug: use vmalloc to back perf mmap() buffers"
1630 depends on PERF_EVENTS && DEBUG_KERNEL
1631 select PERF_USE_VMALLOC
1633 Use vmalloc memory to back perf mmap() buffers.
1635 Mostly useful for debugging the vmalloc code on platforms
1636 that don't require it.
1642 config VM_EVENT_COUNTERS
1644 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1646 VM event counters are needed for event counts to be shown.
1647 This option allows the disabling of the VM event counters
1648 on EXPERT systems. /proc/vmstat will only show page counts
1649 if VM event counters are disabled.
1653 bool "Enable SLUB debugging support" if EXPERT
1654 depends on SLUB && SYSFS
1656 SLUB has extensive debug support features. Disabling these can
1657 result in significant savings in code size. This also disables
1658 SLUB sysfs support. /sys/slab will not exist and there will be
1659 no support for cache validation etc.
1662 bool "Disable heap randomization"
1665 Randomizing heap placement makes heap exploits harder, but it
1666 also breaks ancient binaries (including anything libc5 based).
1667 This option changes the bootup default to heap randomization
1668 disabled, and can be overridden at runtime by setting
1669 /proc/sys/kernel/randomize_va_space to 2.
1671 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1674 prompt "Choose SLAB allocator"
1677 This option allows to select a slab allocator.
1682 The regular slab allocator that is established and known to work
1683 well in all environments. It organizes cache hot objects in
1684 per cpu and per node queues.
1687 bool "SLUB (Unqueued Allocator)"
1689 SLUB is a slab allocator that minimizes cache line usage
1690 instead of managing queues of cached objects (SLAB approach).
1691 Per cpu caching is realized using slabs of objects instead
1692 of queues of objects. SLUB can use memory efficiently
1693 and has enhanced diagnostics. SLUB is the default choice for
1698 bool "SLOB (Simple Allocator)"
1700 SLOB replaces the stock allocator with a drastically simpler
1701 allocator. SLOB is generally more space efficient but
1702 does not perform as well on large systems.
1706 config SLUB_CPU_PARTIAL
1708 depends on SLUB && SMP
1709 bool "SLUB per cpu partial cache"
1711 Per cpu partial caches accellerate objects allocation and freeing
1712 that is local to a processor at the price of more indeterminism
1713 in the latency of the free. On overflow these caches will be cleared
1714 which requires the taking of locks that may cause latency spikes.
1715 Typically one would choose no for a realtime system.
1717 config MMAP_ALLOW_UNINITIALIZED
1718 bool "Allow mmapped anonymous memory to be uninitialized"
1719 depends on EXPERT && !MMU
1722 Normally, and according to the Linux spec, anonymous memory obtained
1723 from mmap() has it's contents cleared before it is passed to
1724 userspace. Enabling this config option allows you to request that
1725 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1726 providing a huge performance boost. If this option is not enabled,
1727 then the flag will be ignored.
1729 This is taken advantage of by uClibc's malloc(), and also by
1730 ELF-FDPIC binfmt's brk and stack allocator.
1732 Because of the obvious security issues, this option should only be
1733 enabled on embedded devices where you control what is run in
1734 userspace. Since that isn't generally a problem on no-MMU systems,
1735 it is normally safe to say Y here.
1737 See Documentation/nommu-mmap.txt for more information.
1739 config SYSTEM_TRUSTED_KEYRING
1740 bool "Provide system-wide ring of trusted keys"
1743 Provide a system keyring to which trusted keys can be added. Keys in
1744 the keyring are considered to be trusted. Keys may be added at will
1745 by the kernel from compiled-in data and from hardware key stores, but
1746 userspace may only add extra keys if those keys can be verified by
1747 keys already in the keyring.
1749 Keys in this keyring are used by module signature checking.
1752 bool "Profiling support"
1754 Say Y here to enable the extended profiling support mechanisms used
1755 by profilers such as OProfile.
1758 # Place an empty function call at each tracepoint site. Can be
1759 # dynamically changed for a probe function.
1764 source "arch/Kconfig"
1766 endmenu # General setup
1768 config HAVE_GENERIC_DMA_COHERENT
1775 depends on SLAB || SLUB_DEBUG
1783 default 0 if BASE_FULL
1784 default 1 if !BASE_FULL
1787 bool "Enable loadable module support"
1790 Kernel modules are small pieces of compiled code which can
1791 be inserted in the running kernel, rather than being
1792 permanently built into the kernel. You use the "modprobe"
1793 tool to add (and sometimes remove) them. If you say Y here,
1794 many parts of the kernel can be built as modules (by
1795 answering M instead of Y where indicated): this is most
1796 useful for infrequently used options which are not required
1797 for booting. For more information, see the man pages for
1798 modprobe, lsmod, modinfo, insmod and rmmod.
1800 If you say Y here, you will need to run "make
1801 modules_install" to put the modules under /lib/modules/
1802 where modprobe can find them (you may need to be root to do
1809 config MODULE_FORCE_LOAD
1810 bool "Forced module loading"
1813 Allow loading of modules without version information (ie. modprobe
1814 --force). Forced module loading sets the 'F' (forced) taint flag and
1815 is usually a really bad idea.
1817 config MODULE_UNLOAD
1818 bool "Module unloading"
1820 Without this option you will not be able to unload any
1821 modules (note that some modules may not be unloadable
1822 anyway), which makes your kernel smaller, faster
1823 and simpler. If unsure, say Y.
1825 config MODULE_FORCE_UNLOAD
1826 bool "Forced module unloading"
1827 depends on MODULE_UNLOAD
1829 This option allows you to force a module to unload, even if the
1830 kernel believes it is unsafe: the kernel will remove the module
1831 without waiting for anyone to stop using it (using the -f option to
1832 rmmod). This is mainly for kernel developers and desperate users.
1836 bool "Module versioning support"
1838 Usually, you have to use modules compiled with your kernel.
1839 Saying Y here makes it sometimes possible to use modules
1840 compiled for different kernels, by adding enough information
1841 to the modules to (hopefully) spot any changes which would
1842 make them incompatible with the kernel you are running. If
1845 config MODULE_SRCVERSION_ALL
1846 bool "Source checksum for all modules"
1848 Modules which contain a MODULE_VERSION get an extra "srcversion"
1849 field inserted into their modinfo section, which contains a
1850 sum of the source files which made it. This helps maintainers
1851 see exactly which source was used to build a module (since
1852 others sometimes change the module source without updating
1853 the version). With this option, such a "srcversion" field
1854 will be created for all modules. If unsure, say N.
1857 bool "Module signature verification"
1859 select SYSTEM_TRUSTED_KEYRING
1862 select ASYMMETRIC_KEY_TYPE
1863 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1864 select PUBLIC_KEY_ALGO_RSA
1867 select X509_CERTIFICATE_PARSER
1869 Check modules for valid signatures upon load: the signature
1870 is simply appended to the module. For more information see
1871 Documentation/module-signing.txt.
1873 !!!WARNING!!! If you enable this option, you MUST make sure that the
1874 module DOES NOT get stripped after being signed. This includes the
1875 debuginfo strip done by some packagers (such as rpmbuild) and
1876 inclusion into an initramfs that wants the module size reduced.
1878 config MODULE_SIG_FORCE
1879 bool "Require modules to be validly signed"
1880 depends on MODULE_SIG
1882 Reject unsigned modules or signed modules for which we don't have a
1883 key. Without this, such modules will simply taint the kernel.
1885 config MODULE_SIG_ALL
1886 bool "Automatically sign all modules"
1888 depends on MODULE_SIG
1890 Sign all modules during make modules_install. Without this option,
1891 modules must be signed manually, using the scripts/sign-file tool.
1893 comment "Do not forget to sign required modules with scripts/sign-file"
1894 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1897 prompt "Which hash algorithm should modules be signed with?"
1898 depends on MODULE_SIG
1900 This determines which sort of hashing algorithm will be used during
1901 signature generation. This algorithm _must_ be built into the kernel
1902 directly so that signature verification can take place. It is not
1903 possible to load a signed module containing the algorithm to check
1904 the signature on that module.
1906 config MODULE_SIG_SHA1
1907 bool "Sign modules with SHA-1"
1910 config MODULE_SIG_SHA224
1911 bool "Sign modules with SHA-224"
1912 select CRYPTO_SHA256
1914 config MODULE_SIG_SHA256
1915 bool "Sign modules with SHA-256"
1916 select CRYPTO_SHA256
1918 config MODULE_SIG_SHA384
1919 bool "Sign modules with SHA-384"
1920 select CRYPTO_SHA512
1922 config MODULE_SIG_SHA512
1923 bool "Sign modules with SHA-512"
1924 select CRYPTO_SHA512
1928 config MODULE_SIG_HASH
1930 depends on MODULE_SIG
1931 default "sha1" if MODULE_SIG_SHA1
1932 default "sha224" if MODULE_SIG_SHA224
1933 default "sha256" if MODULE_SIG_SHA256
1934 default "sha384" if MODULE_SIG_SHA384
1935 default "sha512" if MODULE_SIG_SHA512
1937 config MODULE_COMPRESS
1938 bool "Compress modules on installation"
1941 This option compresses the kernel modules when 'make
1942 modules_install' is run.
1944 The modules will be compressed either using gzip or xz depend on the
1945 choice made in "Compression algorithm".
1947 module-init-tools has support for gzip format while kmod handle gzip
1948 and xz compressed modules.
1950 When a kernel module is installed from outside of the main kernel
1951 source and uses the Kbuild system for installing modules then that
1952 kernel module will also be compressed when it is installed.
1954 This option provides little benefit when the modules are to be used inside
1955 an initrd or initramfs, it generally is more efficient to compress the whole
1956 initrd or initramfs instead.
1958 This is fully compatible with signed modules while the signed module is
1959 compressed. module-init-tools or kmod handles decompression and provide to
1960 other layer the uncompressed but signed payload.
1963 prompt "Compression algorithm"
1964 depends on MODULE_COMPRESS
1965 default MODULE_COMPRESS_GZIP
1967 This determines which sort of compression will be used during
1968 'make modules_install'.
1970 GZIP (default) and XZ are supported.
1972 config MODULE_COMPRESS_GZIP
1975 config MODULE_COMPRESS_XZ
1982 config INIT_ALL_POSSIBLE
1985 Back when each arch used to define their own cpu_online_mask and
1986 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1987 with all 1s, and others with all 0s. When they were centralised,
1988 it was better to provide this option than to break all the archs
1989 and have several arch maintainers pursuing me down dark alleys.
1994 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1996 Need stop_machine() primitive.
1998 source "block/Kconfig"
2000 config PREEMPT_NOTIFIERS
2007 # Can be selected by architectures with broken toolchains
2008 # that get confused by correct const<->read_only section
2010 config BROKEN_RODATA
2016 Build a simple ASN.1 grammar compiler that produces a bytecode output
2017 that can be interpreted by the ASN.1 stream decoder and used to
2018 inform it as to what tags are to be expected in a stream and what
2019 functions to call on what tags.
2021 source "kernel/Kconfig.locks"