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Edit File: Kconfig

# SPDX-License-Identifier: GPL-2.0-only config CC_VERSION_TEXT string default "$(CC_VERSION_TEXT)" help This is used in unclear ways: - Re-run Kconfig when the compiler is updated The 'default' property references the environment variable, CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd. When the compiler is updated, Kconfig will be invoked. - Ensure full rebuild when the compiler is updated include/linux/compiler-version.h contains this option in the comment line so fixdep adds include/config/CC_VERSION_TEXT into the auto-generated dependency. When the compiler is updated, syncconfig will touch it and then every file will be rebuilt. config CC_IS_GCC def_bool $(success,test "$(cc-name)" = GCC) config GCC_VERSION int default $(cc-version) if CC_IS_GCC default 0 config CC_IS_CLANG def_bool $(success,test "$(cc-name)" = Clang) config CLANG_VERSION int default $(cc-version) if CC_IS_CLANG default 0 config AS_IS_GNU def_bool $(success,test "$(as-name)" = GNU) config AS_IS_LLVM def_bool $(success,test "$(as-name)" = LLVM) config AS_VERSION int # Use clang version if this is the integrated assembler default CLANG_VERSION if AS_IS_LLVM default $(as-version) config LD_IS_BFD def_bool $(success,test "$(ld-name)" = BFD) config LD_VERSION int default $(ld-version) if LD_IS_BFD default 0 config LD_IS_LLD def_bool $(success,test "$(ld-name)" = LLD) config LLD_VERSION int default $(ld-version) if LD_IS_LLD default 0 config CC_CAN_LINK bool default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag)) config CC_CAN_LINK_STATIC bool default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static) config CC_HAS_ASM_GOTO def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) config CC_HAS_ASM_GOTO_OUTPUT depends on CC_HAS_ASM_GOTO def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null) config CC_HAS_ASM_GOTO_TIED_OUTPUT depends on CC_HAS_ASM_GOTO_OUTPUT # Detect buggy gcc and clang, fixed in gcc-11 clang-14. def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null) config TOOLS_SUPPORT_RELR def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh) config CC_HAS_ASM_INLINE def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) config CC_HAS_NO_PROFILE_FN_ATTR def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) config PAHOLE_VERSION int default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) config CONSTRUCTORS bool config IRQ_WORK bool config BUILDTIME_TABLE_SORT bool config THREAD_INFO_IN_TASK bool help Select this to move thread_info off the stack into task_struct. To make this work, an arch will need to remove all thread_info fields except flags and fix any runtime bugs. One subtle change that will be needed is to use try_get_task_stack() and put_task_stack() in save_thread_stack_tsk() and get_wchan(). menu "General setup" config BROKEN bool config BROKEN_ON_SMP bool depends on BROKEN || !SMP default y config INIT_ENV_ARG_LIMIT int default 32 if !UML default 128 if UML help Maximum of each of the number of arguments and environment variables passed to init from the kernel command line. config COMPILE_TEST bool "Compile also drivers which will not load" depends on HAS_IOMEM help Some drivers can be compiled on a different platform than they are intended to be run on. Despite they cannot be loaded there (or even when they load they cannot be used due to missing HW support), developers still, opposing to distributors, might want to build such drivers to compile-test them. If you are a developer and want to build everything available, say Y here. If you are a user/distributor, say N here to exclude useless drivers to be distributed. config WERROR bool "Compile the kernel with warnings as errors" default COMPILE_TEST help A kernel build should not cause any compiler warnings, and this enables the '-Werror' flag to enforce that rule by default. However, if you have a new (or very old) compiler with odd and unusual warnings, or you have some architecture with problems, you may need to disable this config option in order to successfully build the kernel. If in doubt, say Y. config UAPI_HEADER_TEST bool "Compile test UAPI headers" depends on HEADERS_INSTALL && CC_CAN_LINK help Compile test headers exported to user-space to ensure they are self-contained, i.e. compilable as standalone units. If you are a developer or tester and want to ensure the exported headers are self-contained, say Y here. Otherwise, choose N. config LOCALVERSION string "Local version - append to kernel release" help Append an extra string to the end of your kernel version. This will show up when you type uname, for example. The string you set here will be appended after the contents of any files with a filename matching localversion* in your object and source tree, in that order. Your total string can be a maximum of 64 characters. config LOCALVERSION_AUTO bool "Automatically append version information to the version string" default y depends on !COMPILE_TEST help This will try to automatically determine if the current tree is a release tree by looking for git tags that belong to the current top of tree revision. A string of the format -gxxxxxxxx will be added to the localversion if a git-based tree is found. The string generated by this will be appended after any matching localversion* files, and after the value set in CONFIG_LOCALVERSION. (The actual string used here is the first eight characters produced by running the command: $ git rev-parse --verify HEAD which is done within the script "scripts/setlocalversion".) config BUILD_SALT string "Build ID Salt" default "" help The build ID is used to link binaries and their debug info. Setting this option will use the value in the calculation of the build id. This is mostly useful for distributions which want to ensure the build is unique between builds. It's safe to leave the default. config HAVE_KERNEL_GZIP bool config HAVE_KERNEL_BZIP2 bool config HAVE_KERNEL_LZMA bool config HAVE_KERNEL_XZ bool config HAVE_KERNEL_LZO bool config HAVE_KERNEL_LZ4 bool config HAVE_KERNEL_ZSTD bool config HAVE_KERNEL_UNCOMPRESSED bool choice prompt "Kernel compression mode" default KERNEL_GZIP depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED help The linux kernel is a kind of self-extracting executable. Several compression algorithms are available, which differ in efficiency, compression and decompression speed. Compression speed is only relevant when building a kernel. Decompression speed is relevant at each boot. If you have any problems with bzip2 or lzma compressed kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older version of this functionality (bzip2 only), for 2.4, was supplied by Christian Ludwig) High compression options are mostly useful for users, who are low on disk space (embedded systems), but for whom ram size matters less. If in doubt, select 'gzip' config KERNEL_GZIP bool "Gzip" depends on HAVE_KERNEL_GZIP help The old and tried gzip compression. It provides a good balance between compression ratio and decompression speed. config KERNEL_BZIP2 bool "Bzip2" depends on HAVE_KERNEL_BZIP2 help Its compression ratio and speed is intermediate. Decompression speed is slowest among the choices. The kernel size is about 10% smaller with bzip2, in comparison to gzip. Bzip2 uses a large amount of memory. For modern kernels you will need at least 8MB RAM or more for booting. config KERNEL_LZMA bool "LZMA" depends on HAVE_KERNEL_LZMA help This compression algorithm's ratio is best. Decompression speed is between gzip and bzip2. Compression is slowest. The kernel size is about 33% smaller with LZMA in comparison to gzip. config KERNEL_XZ bool "XZ" depends on HAVE_KERNEL_XZ help XZ uses the LZMA2 algorithm and instruction set specific BCJ filters which can improve compression ratio of executable code. The size of the kernel is about 30% smaller with XZ in comparison to gzip. On architectures for which there is a BCJ filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ will create a few percent smaller kernel than plain LZMA. The speed is about the same as with LZMA: The decompression speed of XZ is better than that of bzip2 but worse than gzip and LZO. Compression is slow. config KERNEL_LZO bool "LZO" depends on HAVE_KERNEL_LZO help Its compression ratio is the poorest among the choices. The kernel size is about 10% bigger than gzip; however its speed (both compression and decompression) is the fastest. config KERNEL_LZ4 bool "LZ4" depends on HAVE_KERNEL_LZ4 help LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. A preliminary version of LZ4 de/compression tool is available at <https://code.google.com/p/lz4/>. Its compression ratio is worse than LZO. The size of the kernel is about 8% bigger than LZO. But the decompression speed is faster than LZO. config KERNEL_ZSTD bool "ZSTD" depends on HAVE_KERNEL_ZSTD help ZSTD is a compression algorithm targeting intermediate compression with fast decompression speed. It will compress better than GZIP and decompress around the same speed as LZO, but slower than LZ4. You will need at least 192 KB RAM or more for booting. The zstd command line tool is required for compression. config KERNEL_UNCOMPRESSED bool "None" depends on HAVE_KERNEL_UNCOMPRESSED help Produce uncompressed kernel image. This option is usually not what you want. It is useful for debugging the kernel in slow simulation environments, where decompressing and moving the kernel is awfully slow. This option allows early boot code to skip the decompressor and jump right at uncompressed kernel image. endchoice config DEFAULT_INIT string "Default init path" default "" help This option determines the default init for the system if no init= option is passed on the kernel command line. If the requested path is not present, we will still then move on to attempting further locations (e.g. /sbin/init, etc). If this is empty, we will just use the fallback list when init= is not passed. config DEFAULT_HOSTNAME string "Default hostname" default "(none)" help This option determines the default system hostname before userspace calls sethostname(2). The kernel traditionally uses "(none)" here, but you may wish to use a different default here to make a minimal system more usable with less configuration. # # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can # add proper SWAP support to them, in which case this can be remove. # config ARCH_NO_SWAP bool config VERSION_SIGNATURE string "Arbitrary version signature" help This string will be created in a file, /proc/version_signature. It is useful in determining arbitrary data about your kernel. For instance, if you have several kernels of the same version, but need to keep track of a revision of the same kernel, but not affect it's ability to load compatible modules, this is the easiest way to do that. config SWAP bool "Support for paging of anonymous memory (swap)" depends on MMU && BLOCK && !ARCH_NO_SWAP default y help This option allows you to choose whether you want to have support for so called swap devices or swap files in your kernel that are used to provide more virtual memory than the actual RAM present in your computer. If unsure say Y. config SYSVIPC bool "System V IPC" help Inter Process Communication is a suite of library functions and system calls which let processes (running programs) synchronize and exchange information. It is generally considered to be a good thing, and some programs won't run unless you say Y here. In particular, if you want to run the DOS emulator dosemu under Linux (read the DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), you'll need to say Y here. You can find documentation about IPC with "info ipc" and also in section 6.4 of the Linux Programmer's Guide, available from <http://www.tldp.org/guides.html>. config SYSVIPC_SYSCTL bool depends on SYSVIPC depends on SYSCTL default y config POSIX_MQUEUE bool "POSIX Message Queues" depends on NET help POSIX variant of message queues is a part of IPC. In POSIX message queues every message has a priority which decides about succession of receiving it by a process. If you want to compile and run programs written e.g. for Solaris with use of its POSIX message queues (functions mq_*) say Y here. POSIX message queues are visible as a filesystem called 'mqueue' and can be mounted somewhere if you want to do filesystem operations on message queues. If unsure, say Y. config POSIX_MQUEUE_SYSCTL bool depends on POSIX_MQUEUE depends on SYSCTL default y config WATCH_QUEUE bool "General notification queue" default n help This is a general notification queue for the kernel to pass events to userspace by splicing them into pipes. It can be used in conjunction with watches for key/keyring change notifications and device notifications. See Documentation/watch_queue.rst config CROSS_MEMORY_ATTACH bool "Enable process_vm_readv/writev syscalls" depends on MMU default y help Enabling this option adds the system calls process_vm_readv and process_vm_writev which allow a process with the correct privileges to directly read from or write to another process' address space. See the man page for more details. config USELIB bool "uselib syscall" def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION help This option enables the uselib syscall, a system call used in the dynamic linker from libc5 and earlier. glibc does not use this system call. If you intend to run programs built on libc5 or earlier, you may need to enable this syscall. Current systems running glibc can safely disable this. config AUDIT bool "Auditing support" depends on NET help Enable auditing infrastructure that can be used with another kernel subsystem, such as SELinux (which requires this for logging of avc messages output). System call auditing is included on architectures which support it. config HAVE_ARCH_AUDITSYSCALL bool config AUDITSYSCALL def_bool y depends on AUDIT && HAVE_ARCH_AUDITSYSCALL select FSNOTIFY source "kernel/irq/Kconfig" source "kernel/time/Kconfig" source "kernel/bpf/Kconfig" source "kernel/Kconfig.preempt" menu "CPU/Task time and stats accounting" config VIRT_CPU_ACCOUNTING bool choice prompt "Cputime accounting" default TICK_CPU_ACCOUNTING if !PPC64 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 # Kind of a stub config for the pure tick based cputime accounting config TICK_CPU_ACCOUNTING bool "Simple tick based cputime accounting" depends on !S390 && !NO_HZ_FULL help This is the basic tick based cputime accounting that maintains statistics about user, system and idle time spent on per jiffies granularity. If unsure, say Y. config VIRT_CPU_ACCOUNTING_NATIVE bool "Deterministic task and CPU time accounting" depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL select VIRT_CPU_ACCOUNTING help Select this option to enable more accurate task and CPU time accounting. This is done by reading a CPU counter on each kernel entry and exit and on transitions within the kernel between system, softirq and hardirq state, so there is a small performance impact. In the case of s390 or IBM POWER > 5, this also enables accounting of stolen time on logically-partitioned systems. config VIRT_CPU_ACCOUNTING_GEN bool "Full dynticks CPU time accounting" depends on HAVE_CONTEXT_TRACKING depends on HAVE_VIRT_CPU_ACCOUNTING_GEN depends on GENERIC_CLOCKEVENTS select VIRT_CPU_ACCOUNTING select CONTEXT_TRACKING help Select this option to enable task and CPU time accounting on full dynticks systems. This accounting is implemented by watching every kernel-user boundaries using the context tracking subsystem. The accounting is thus performed at the expense of some significant overhead. For now this is only useful if you are working on the full dynticks subsystem development. If unsure, say N. endchoice config IRQ_TIME_ACCOUNTING bool "Fine granularity task level IRQ time accounting" depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE help Select this option to enable fine granularity task irq time accounting. This is done by reading a timestamp on each transitions between softirq and hardirq state, so there can be a small performance impact. If in doubt, say N here. config HAVE_SCHED_AVG_IRQ def_bool y depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING depends on SMP config SCHED_THERMAL_PRESSURE bool default y if ARM && ARM_CPU_TOPOLOGY default y if ARM64 depends on SMP depends on CPU_FREQ_THERMAL help Select this option to enable thermal pressure accounting in the scheduler. Thermal pressure is the value conveyed to the scheduler that reflects the reduction in CPU compute capacity resulted from thermal throttling. Thermal throttling occurs when the performance of a CPU is capped due to high operating temperatures. If selected, the scheduler will be able to balance tasks accordingly, i.e. put less load on throttled CPUs than on non/less throttled ones. This requires the architecture to implement arch_set_thermal_pressure() and arch_scale_thermal_pressure(). config BSD_PROCESS_ACCT bool "BSD Process Accounting" depends on MULTIUSER help If you say Y here, a user level program will be able to instruct the kernel (via a special system call) to write process accounting information to a file: whenever a process exits, information about that process will be appended to the file by the kernel. The information includes things such as creation time, owning user, command name, memory usage, controlling terminal etc. (the complete list is in the struct acct in <file:include/linux/acct.h>). It is up to the user level program to do useful things with this information. This is generally a good idea, so say Y. config BSD_PROCESS_ACCT_V3 bool "BSD Process Accounting version 3 file format" depends on BSD_PROCESS_ACCT default n help If you say Y here, the process accounting information is written in a new file format that also logs the process IDs of each process and its parent. Note that this file format is incompatible with previous v0/v1/v2 file formats, so you will need updated tools for processing it. A preliminary version of these tools is available at <http://www.gnu.org/software/acct/>. config TASKSTATS bool "Export task/process statistics through netlink" depends on NET depends on MULTIUSER default n help Export selected statistics for tasks/processes through the generic netlink interface. Unlike BSD process accounting, the statistics are available during the lifetime of tasks/processes as responses to commands. Like BSD accounting, they are sent to user space on task exit. Say N if unsure. config TASK_DELAY_ACCT bool "Enable per-task delay accounting" depends on TASKSTATS select SCHED_INFO help Collect information on time spent by a task waiting for system resources like cpu, synchronous block I/O completion and swapping in pages. Such statistics can help in setting a task's priorities relative to other tasks for cpu, io, rss limits etc. Say N if unsure. config TASK_XACCT bool "Enable extended accounting over taskstats" depends on TASKSTATS help Collect extended task accounting data and send the data to userland for processing over the taskstats interface. Say N if unsure. config TASK_IO_ACCOUNTING bool "Enable per-task storage I/O accounting" depends on TASK_XACCT help Collect information on the number of bytes of storage I/O which this task has caused. Say N if unsure. config PSI bool "Pressure stall information tracking" help Collect metrics that indicate how overcommitted the CPU, memory, and IO capacity are in the system. If you say Y here, the kernel will create /proc/pressure/ with the pressure statistics files cpu, memory, and io. These will indicate the share of walltime in which some or all tasks in the system are delayed due to contention of the respective resource. In kernels with cgroup support, cgroups (cgroup2 only) will have cpu.pressure, memory.pressure, and io.pressure files, which aggregate pressure stalls for the grouped tasks only. For more details see Documentation/accounting/psi.rst. Say N if unsure. config PSI_DEFAULT_DISABLED bool "Require boot parameter to enable pressure stall information tracking" default n depends on PSI help If set, pressure stall information tracking will be disabled per default but can be enabled through passing psi=1 on the kernel commandline during boot. This feature adds some code to the task wakeup and sleep paths of the scheduler. The overhead is too low to affect common scheduling-intense workloads in practice (such as webservers, memcache), but it does show up in artificial scheduler stress tests, such as hackbench. If you are paranoid and not sure what the kernel will be used for, say Y. Say N if unsure. endmenu # "CPU/Task time and stats accounting" config CPU_ISOLATION bool "CPU isolation" depends on SMP || COMPILE_TEST default y help Make sure that CPUs running critical tasks are not disturbed by any source of "noise" such as unbound workqueues, timers, kthreads... Unbound jobs get offloaded to housekeeping CPUs. This is driven by the "isolcpus=" boot parameter. Say Y if unsure. source "kernel/rcu/Kconfig" config BUILD_BIN2C bool default n config IKCONFIG tristate "Kernel .config support" help This option enables the complete Linux kernel ".config" file contents to be saved in the kernel. It provides documentation of which kernel options are used in a running kernel or in an on-disk kernel. This information can be extracted from the kernel image file with the script scripts/extract-ikconfig and used as input to rebuild the current kernel or to build another kernel. It can also be extracted from a running kernel by reading /proc/config.gz if enabled (below). config IKCONFIG_PROC bool "Enable access to .config through /proc/config.gz" depends on IKCONFIG && PROC_FS help This option enables access to the kernel configuration file through /proc/config.gz. config IKHEADERS tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz" depends on SYSFS help This option enables access to the in-kernel headers that are generated during the build process. These can be used to build eBPF tracing programs, or similar programs. If you build the headers as a module, a module called kheaders.ko is built which can be loaded on-demand to get access to headers. config LOG_BUF_SHIFT int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" range 12 25 if !H8300 range 12 19 if H8300 default 17 depends on PRINTK help Select the minimal kernel log buffer size as a power of 2. The final size is affected by LOG_CPU_MAX_BUF_SHIFT config parameter, see below. Any higher size also might be forced by "log_buf_len" boot parameter. Examples: 17 => 128 KB 16 => 64 KB 15 => 32 KB 14 => 16 KB 13 => 8 KB 12 => 4 KB config LOG_CPU_MAX_BUF_SHIFT int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" depends on SMP range 0 21 default 12 if !BASE_SMALL default 0 if BASE_SMALL depends on PRINTK help This option allows to increase the default ring buffer size according to the number of CPUs. The value defines the contribution of each CPU as a power of 2. The used space is typically only few lines however it might be much more when problems are reported, e.g. backtraces. The increased size means that a new buffer has to be allocated and the original static one is unused. It makes sense only on systems with more CPUs. Therefore this value is used only when the sum of contributions is greater than the half of the default kernel ring buffer as defined by LOG_BUF_SHIFT. The default values are set so that more than 16 CPUs are needed to trigger the allocation. Also this option is ignored when "log_buf_len" kernel parameter is used as it forces an exact (power of two) size of the ring buffer. The number of possible CPUs is used for this computation ignoring hotplugging making the computation optimal for the worst case scenario while allowing a simple algorithm to be used from bootup. Examples shift values and their meaning: 17 => 128 KB for each CPU 16 => 64 KB for each CPU 15 => 32 KB for each CPU 14 => 16 KB for each CPU 13 => 8 KB for each CPU 12 => 4 KB for each CPU config PRINTK_SAFE_LOG_BUF_SHIFT int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)" range 10 21 default 13 depends on PRINTK help Select the size of an alternate printk per-CPU buffer where messages printed from usafe contexts are temporary stored. One example would be NMI messages, another one - printk recursion. The messages are copied to the main log buffer in a safe context to avoid a deadlock. The value defines the size as a power of 2. Those messages are rare and limited. The largest one is when a backtrace is printed. It usually fits into 4KB. Select 8KB if you want to be on the safe side. Examples: 17 => 128 KB for each CPU 16 => 64 KB for each CPU 15 => 32 KB for each CPU 14 => 16 KB for each CPU 13 => 8 KB for each CPU 12 => 4 KB for each CPU config PRINTK_INDEX bool "Printk indexing debugfs interface" depends on PRINTK && DEBUG_FS help Add support for indexing of all printk formats known at compile time at <debugfs>/printk/index/<module>. This can be used as part of maintaining daemons which monitor /dev/kmsg, as it permits auditing the printk formats present in a kernel, allowing detection of cases where monitored printks are changed or no longer present. There is no additional runtime cost to printk with this enabled. # # Architectures with an unreliable sched_clock() should select this: # config HAVE_UNSTABLE_SCHED_CLOCK bool config GENERIC_SCHED_CLOCK bool menu "Scheduler features" config UCLAMP_TASK bool "Enable utilization clamping for RT/FAIR tasks" depends on CPU_FREQ_GOV_SCHEDUTIL help This feature enables the scheduler to track the clamped utilization of each CPU based on RUNNABLE tasks scheduled on that CPU. With this option, the user can specify the min and max CPU utilization allowed for RUNNABLE tasks. The max utilization defines the maximum frequency a task should use while the min utilization defines the minimum frequency it should use. Both min and max utilization clamp values are hints to the scheduler, aiming at improving its frequency selection policy, but they do not enforce or grant any specific bandwidth for tasks. If in doubt, say N. config UCLAMP_BUCKETS_COUNT int "Number of supported utilization clamp buckets" range 5 20 default 5 depends on UCLAMP_TASK help Defines the number of clamp buckets to use. The range of each bucket will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the number of clamp buckets the finer their granularity and the higher the precision of clamping aggregation and tracking at run-time. For example, with the minimum configuration value we will have 5 clamp buckets tracking 20% utilization each. A 25% boosted tasks will be refcounted in the [20..39]% bucket and will set the bucket clamp effective value to 25%. If a second 30% boosted task should be co-scheduled on the same CPU, that task will be refcounted in the same bucket of the first task and it will boost the bucket clamp effective value to 30%. The clamp effective value of a bucket is reset to its nominal value (20% in the example above) when there are no more tasks refcounted in that bucket. An additional boost/capping margin can be added to some tasks. In the example above the 25% task will be boosted to 30% until it exits the CPU. If that should be considered not acceptable on certain systems, it's always possible to reduce the margin by increasing the number of clamp buckets to trade off used memory for run-time tracking precision. If in doubt, use the default value. endmenu # # For architectures that want to enable the support for NUMA-affine scheduler # balancing logic: # config ARCH_SUPPORTS_NUMA_BALANCING bool # # For architectures that prefer to flush all TLBs after a number of pages # are unmapped instead of sending one IPI per page to flush. The architecture # must provide guarantees on what happens if a clean TLB cache entry is # written after the unmap. Details are in mm/rmap.c near the check for # should_defer_flush. The architecture should also consider if the full flush # and the refill costs are offset by the savings of sending fewer IPIs. config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH bool config CC_HAS_INT128 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT # # For architectures that know their GCC __int128 support is sound # config ARCH_SUPPORTS_INT128 bool # For architectures that (ab)use NUMA to represent different memory regions # all cpu-local but of different latencies, such as SuperH. # config ARCH_WANT_NUMA_VARIABLE_LOCALITY bool config NUMA_BALANCING bool "Memory placement aware NUMA scheduler" depends on ARCH_SUPPORTS_NUMA_BALANCING depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY depends on SMP && NUMA && MIGRATION help This option adds support for automatic NUMA aware memory/task placement. The mechanism is quite primitive and is based on migrating memory when it has references to the node the task is running on. This system will be inactive on UMA systems. config NUMA_BALANCING_DEFAULT_ENABLED bool "Automatically enable NUMA aware memory/task placement" default y depends on NUMA_BALANCING help If set, automatic NUMA balancing will be enabled if running on a NUMA machine. menuconfig CGROUPS bool "Control Group support" select KERNFS help This option adds support for grouping sets of processes together, for use with process control subsystems such as Cpusets, CFS, memory controls or device isolation. See - Documentation/scheduler/sched-design-CFS.rst (CFS) - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation and resource control) Say N if unsure. if CGROUPS config PAGE_COUNTER bool config MEMCG bool "Memory controller" select PAGE_COUNTER select EVENTFD help Provides control over the memory footprint of tasks in a cgroup. config MEMCG_SWAP bool depends on MEMCG && SWAP default y config MEMCG_KMEM bool depends on MEMCG && !SLOB default y config BLK_CGROUP bool "IO controller" depends on BLOCK default n help Generic block IO controller cgroup interface. This is the common cgroup interface which should be used by various IO controlling policies. Currently, CFQ IO scheduler uses it to recognize task groups and control disk bandwidth allocation (proportional time slice allocation) to such task groups. It is also used by bio throttling logic in block layer to implement upper limit in IO rates on a device. This option only enables generic Block IO controller infrastructure. One needs to also enable actual IO controlling logic/policy. For enabling proportional weight division of disk bandwidth in CFQ, set CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set CONFIG_BLK_DEV_THROTTLING=y. See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information. config CGROUP_WRITEBACK bool depends on MEMCG && BLK_CGROUP default y menuconfig CGROUP_SCHED bool "CPU controller" default n help This feature lets CPU scheduler recognize task groups and control CPU bandwidth allocation to such task groups. It uses cgroups to group tasks. if CGROUP_SCHED config FAIR_GROUP_SCHED bool "Group scheduling for SCHED_OTHER" depends on CGROUP_SCHED default CGROUP_SCHED config CFS_BANDWIDTH bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" depends on FAIR_GROUP_SCHED default n help This option allows users to define CPU bandwidth rates (limits) for tasks running within the fair group scheduler. Groups with no limit set are considered to be unconstrained and will run with no restriction. See Documentation/scheduler/sched-bwc.rst for more information. config RT_GROUP_SCHED bool "Group scheduling for SCHED_RR/FIFO" depends on CGROUP_SCHED default n help This feature lets you explicitly allocate real CPU bandwidth to task groups. If enabled, it will also make it impossible to schedule realtime tasks for non-root users until you allocate realtime bandwidth for them. See Documentation/scheduler/sched-rt-group.rst for more information. endif #CGROUP_SCHED config UCLAMP_TASK_GROUP bool "Utilization clamping per group of tasks" depends on CGROUP_SCHED depends on UCLAMP_TASK default n help This feature enables the scheduler to track the clamped utilization of each CPU based on RUNNABLE tasks currently scheduled on that CPU. When this option is enabled, the user can specify a min and max CPU bandwidth which is allowed for each single task in a group. The max bandwidth allows to clamp the maximum frequency a task can use, while the min bandwidth allows to define a minimum frequency a task will always use. When task group based utilization clamping is enabled, an eventually specified task-specific clamp value is constrained by the cgroup specified clamp value. Both minimum and maximum task clamping cannot be bigger than the corresponding clamping defined at task group level. If in doubt, say N. config CGROUP_PIDS bool "PIDs controller" help Provides enforcement of process number limits in the scope of a cgroup. Any attempt to fork more processes than is allowed in the cgroup will fail. PIDs are fundamentally a global resource because it is fairly trivial to reach PID exhaustion before you reach even a conservative kmemcg limit. As a result, it is possible to grind a system to halt without being limited by other cgroup policies. The PIDs controller is designed to stop this from happening. It should be noted that organisational operations (such as attaching to a cgroup hierarchy) will *not* be blocked by the PIDs controller, since the PIDs limit only affects a process's ability to fork, not to attach to a cgroup. config CGROUP_RDMA bool "RDMA controller" help Provides enforcement of RDMA resources defined by IB stack. It is fairly easy for consumers to exhaust RDMA resources, which can result into resource unavailability to other consumers. RDMA controller is designed to stop this from happening. Attaching processes with active RDMA resources to the cgroup hierarchy is allowed even if can cross the hierarchy's limit. config CGROUP_FREEZER bool "Freezer controller" help Provides a way to freeze and unfreeze all tasks in a cgroup. This option affects the ORIGINAL cgroup interface. The cgroup2 memory controller includes important in-kernel memory consumers per default. If you're using cgroup2, say N. config CGROUP_HUGETLB bool "HugeTLB controller" depends on HUGETLB_PAGE select PAGE_COUNTER default n help Provides a cgroup controller for HugeTLB pages. When you enable this, you can put a per cgroup limit on HugeTLB usage. The limit is enforced during page fault. Since HugeTLB doesn't support page reclaim, enforcing the limit at page fault time implies that, the application will get SIGBUS signal if it tries to access HugeTLB pages beyond its limit. This requires the application to know beforehand how much HugeTLB pages it would require for its use. The control group is tracked in the third page lru pointer. This means that we cannot use the controller with huge page less than 3 pages. config CPUSETS bool "Cpuset controller" depends on SMP help This option will let you create and manage CPUSETs which allow dynamically partitioning a system into sets of CPUs and Memory Nodes and assigning tasks to run only within those sets. This is primarily useful on large SMP or NUMA systems. Say N if unsure. config PROC_PID_CPUSET bool "Include legacy /proc/<pid>/cpuset file" depends on CPUSETS default y config CGROUP_DEVICE bool "Device controller" help Provides a cgroup controller implementing whitelists for devices which a process in the cgroup can mknod or open. config CGROUP_CPUACCT bool "Simple CPU accounting controller" help Provides a simple controller for monitoring the total CPU consumed by the tasks in a cgroup. config CGROUP_PERF bool "Perf controller" depends on PERF_EVENTS help This option extends the perf per-cpu mode to restrict monitoring to threads which belong to the cgroup specified and run on the designated cpu. Or this can be used to have cgroup ID in samples so that it can monitor performance events among cgroups. Say N if unsure. config CGROUP_BPF bool "Support for eBPF programs attached to cgroups" depends on BPF_SYSCALL select SOCK_CGROUP_DATA help Allow attaching eBPF programs to a cgroup using the bpf(2) syscall command BPF_PROG_ATTACH. In which context these programs are accessed depends on the type of attachment. For instance, programs that are attached using BPF_CGROUP_INET_INGRESS will be executed on the ingress path of inet sockets. config CGROUP_MISC bool "Misc resource controller" default n help Provides a controller for miscellaneous resources on a host. Miscellaneous scalar resources are the resources on the host system which cannot be abstracted like the other cgroups. This controller tracks and limits the miscellaneous resources used by a process attached to a cgroup hierarchy. For more information, please check misc cgroup section in /Documentation/admin-guide/cgroup-v2.rst. config CGROUP_DEBUG bool "Debug controller" default n depends on DEBUG_KERNEL help This option enables a simple controller that exports debugging information about the cgroups framework. This controller is for control cgroup debugging only. Its interfaces are not stable. Say N. config SOCK_CGROUP_DATA bool default n endif # CGROUPS menuconfig NAMESPACES bool "Namespaces support" if EXPERT depends on MULTIUSER default !EXPERT help Provides the way to make tasks work with different objects using the same id. For example same IPC id may refer to different objects or same user id or pid may refer to different tasks when used in different namespaces. if NAMESPACES config UTS_NS bool "UTS namespace" default y help In this namespace tasks see different info provided with the uname() system call config TIME_NS bool "TIME namespace" depends on GENERIC_VDSO_TIME_NS default y help In this namespace boottime and monotonic clocks can be set. The time will keep going with the same pace. config IPC_NS bool "IPC namespace" depends on (SYSVIPC || POSIX_MQUEUE) default y help In this namespace tasks work with IPC ids which correspond to different IPC objects in different namespaces. config USER_NS bool "User namespace" default n help This allows containers, i.e. vservers, to use user namespaces to provide different user info for different servers. When user namespaces are enabled in the kernel it is recommended that the MEMCG option also be enabled and that user-space use the memory control groups to limit the amount of memory a memory unprivileged users can use. If unsure, say N. config PID_NS bool "PID Namespaces" default y help Support process id namespaces. This allows having multiple processes with the same pid as long as they are in different pid namespaces. This is a building block of containers. config NET_NS bool "Network namespace" depends on NET default y help Allow user space to create what appear to be multiple instances of the network stack. endif # NAMESPACES config CHECKPOINT_RESTORE bool "Checkpoint/restore support" select PROC_CHILDREN select KCMP default n help Enables additional kernel features in a sake of checkpoint/restore. In particular it adds auxiliary prctl codes to setup process text, data and heap segment sizes, and a few additional /proc filesystem entries. If unsure, say N here. config SCHED_AUTOGROUP bool "Automatic process group scheduling" select CGROUPS select CGROUP_SCHED select FAIR_GROUP_SCHED help This option optimizes the scheduler for common desktop workloads by automatically creating and populating task groups. This separation of workloads isolates aggressive CPU burners (like build jobs) from desktop applications. Task group autogeneration is currently based upon task session. config SYSFS_DEPRECATED bool "Enable deprecated sysfs features to support old userspace tools" depends on SYSFS default n help This option adds code that switches the layout of the "block" class devices, to not show up in /sys/class/block/, but only in /sys/block/. This switch is only active when the sysfs.deprecated=1 boot option is passed or the SYSFS_DEPRECATED_V2 option is set. This option allows new kernels to run on old distributions and tools, which might get confused by /sys/class/block/. Since 2007/2008 all major distributions and tools handle this just fine. Recent distributions and userspace tools after 2009/2010 depend on the existence of /sys/class/block/, and will not work with this option enabled. Only if you are using a new kernel on an old distribution, you might need to say Y here. config SYSFS_DEPRECATED_V2 bool "Enable deprecated sysfs features by default" default n depends on SYSFS depends on SYSFS_DEPRECATED help Enable deprecated sysfs by default. See the CONFIG_SYSFS_DEPRECATED option for more details about this option. Only if you are using a new kernel on an old distribution, you might need to say Y here. Even then, odds are you would not need it enabled, you can always pass the boot option if absolutely necessary. config RELAY bool "Kernel->user space relay support (formerly relayfs)" select IRQ_WORK help This option enables support for relay interface support in certain file systems (such as debugfs). It is designed to provide an efficient mechanism for tools and facilities to relay large amounts of data from kernel space to user space. If unsure, say N. config BLK_DEV_INITRD bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" help The initial RAM filesystem is a ramfs which is loaded by the boot loader (loadlin or lilo) and that is mounted as root before the normal boot procedure. It is typically used to load modules needed to mount the "real" root file system, etc. See <file:Documentation/admin-guide/initrd.rst> for details. If RAM disk support (BLK_DEV_RAM) is also included, this also enables initial RAM disk (initrd) support and adds 15 Kbytes (more on some other architectures) to the kernel size. If unsure say Y. if BLK_DEV_INITRD source "usr/Kconfig" endif config BOOT_CONFIG bool "Boot config support" select BLK_DEV_INITRD help Extra boot config allows system admin to pass a config file as complemental extension of kernel cmdline when booting. The boot config file must be attached at the end of initramfs with checksum, size and magic word. See <file:Documentation/admin-guide/bootconfig.rst> for details. If unsure, say Y. choice prompt "Compiler optimization level" default CC_OPTIMIZE_FOR_PERFORMANCE config CC_OPTIMIZE_FOR_PERFORMANCE bool "Optimize for performance (-O2)" help This is the default optimization level for the kernel, building with the "-O2" compiler flag for best performance and most helpful compile-time warnings. config CC_OPTIMIZE_FOR_PERFORMANCE_O3 bool "Optimize more for performance (-O3)" depends on ARC help Choosing this option will pass "-O3" to your compiler to optimize the kernel yet more for performance. config CC_OPTIMIZE_FOR_SIZE bool "Optimize for size (-Os)" help Choosing this option will pass "-Os" to your compiler resulting in a smaller kernel. endchoice config HAVE_LD_DEAD_CODE_DATA_ELIMINATION bool help This requires that the arch annotates or otherwise protects its external entry points from being discarded. Linker scripts must also merge .text.*, .data.*, and .bss.* correctly into output sections. Care must be taken not to pull in unrelated sections (e.g., '.text.init'). Typically '.' in section names is used to distinguish them from label names / C identifiers. config LD_DEAD_CODE_DATA_ELIMINATION bool "Dead code and data elimination (EXPERIMENTAL)" depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION depends on EXPERT depends on $(cc-option,-ffunction-sections -fdata-sections) depends on $(ld-option,--gc-sections) help Enable this if you want to do dead code and data elimination with the linker by compiling with -ffunction-sections -fdata-sections, and linking with --gc-sections. This can reduce on disk and in-memory size of the kernel code and static data, particularly for small configs and on small systems. This has the possibility of introducing silently broken kernel if the required annotations are not present. This option is not well tested yet, so use at your own risk. config LD_ORPHAN_WARN def_bool y depends on ARCH_WANT_LD_ORPHAN_WARN depends on !LD_IS_LLD || LLD_VERSION >= 110000 depends on $(ld-option,--orphan-handling=warn) config SYSCTL bool config HAVE_UID16 bool config SYSCTL_EXCEPTION_TRACE bool help Enable support for /proc/sys/debug/exception-trace. config SYSCTL_ARCH_UNALIGN_NO_WARN bool help Enable support for /proc/sys/kernel/ignore-unaligned-usertrap Allows arch to define/use @no_unaligned_warning to possibly warn about unaligned access emulation going on under the hood. config SYSCTL_ARCH_UNALIGN_ALLOW bool help Enable support for /proc/sys/kernel/unaligned-trap Allows arches to define/use @unaligned_enabled to runtime toggle the unaligned access emulation. see arch/parisc/kernel/unaligned.c for reference config HAVE_PCSPKR_PLATFORM bool # interpreter that classic socket filters depend on config BPF bool menuconfig EXPERT bool "Configure standard kernel features (expert users)" # Unhide debug options, to make the on-by-default options visible select DEBUG_KERNEL help This option allows certain base kernel options and settings to be disabled or tweaked. This is for specialized environments which can tolerate a "non-standard" kernel. Only use this if you really know what you are doing. config UID16 bool "Enable 16-bit UID system calls" if EXPERT depends on HAVE_UID16 && MULTIUSER default y help This enables the legacy 16-bit UID syscall wrappers. config MULTIUSER bool "Multiple users, groups and capabilities support" if EXPERT default y help This option enables support for non-root users, groups and capabilities. If you say N here, all processes will run with UID 0, GID 0, and all possible capabilities. Saying N here also compiles out support for system calls related to UIDs, GIDs, and capabilities, such as setuid, setgid, and capset. If unsure, say Y here. config SGETMASK_SYSCALL bool "sgetmask/ssetmask syscalls support" if EXPERT def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH help sys_sgetmask and sys_ssetmask are obsolete system calls no longer supported in libc but still enabled by default in some architectures. If unsure, leave the default option here. config SYSFS_SYSCALL bool "Sysfs syscall support" if EXPERT default y help sys_sysfs is an obsolete system call no longer supported in libc. Note that disabling this option is more secure but might break compatibility with some systems. If unsure say Y here. config FHANDLE bool "open by fhandle syscalls" if EXPERT select EXPORTFS default y help If you say Y here, a user level program will be able to map file names to handle and then later use the handle for different file system operations. This is useful in implementing userspace file servers, which now track files using handles instead of names. The handle would remain the same even if file names get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) syscalls. config POSIX_TIMERS bool "Posix Clocks & timers" if EXPERT default y help This includes native support for POSIX timers to the kernel. Some embedded systems have no use for them and therefore they can be configured out to reduce the size of the kernel image. When this option is disabled, the following syscalls won't be available: timer_create, timer_gettime: timer_getoverrun, timer_settime, timer_delete, clock_adjtime, getitimer, setitimer, alarm. Furthermore, the clock_settime, clock_gettime, clock_getres and clock_nanosleep syscalls will be limited to CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only. If unsure say y. config PRINTK default y bool "Enable support for printk" if EXPERT select IRQ_WORK help This option enables normal printk support. Removing it eliminates most of the message strings from the kernel image and makes the kernel more or less silent. As this makes it very difficult to diagnose system problems, saying N here is strongly discouraged. config BUG bool "BUG() support" if EXPERT default y help Disabling this option eliminates support for BUG and WARN, reducing the size of your kernel image and potentially quietly ignoring numerous fatal conditions. You should only consider disabling this option for embedded systems with no facilities for reporting errors. Just say Y. config ELF_CORE depends on COREDUMP default y bool "Enable ELF core dumps" if EXPERT help Enable support for generating core dumps. Disabling saves about 4k. config PCSPKR_PLATFORM bool "Enable PC-Speaker support" if EXPERT depends on HAVE_PCSPKR_PLATFORM select I8253_LOCK default y help This option allows to disable the internal PC-Speaker support, saving some memory. config BASE_FULL default y bool "Enable full-sized data structures for core" if EXPERT help Disabling this option reduces the size of miscellaneous core kernel data structures. This saves memory on small machines, but may reduce performance. config FUTEX bool "Enable futex support" if EXPERT default y imply RT_MUTEXES help Disabling this option will cause the kernel to be built without support for "fast userspace mutexes". The resulting kernel may not run glibc-based applications correctly. config FUTEX_PI bool depends on FUTEX && RT_MUTEXES default y config HAVE_FUTEX_CMPXCHG bool depends on FUTEX help Architectures should select this if futex_atomic_cmpxchg_inatomic() is implemented and always working. This removes a couple of runtime checks. config EPOLL bool "Enable eventpoll support" if EXPERT default y help Disabling this option will cause the kernel to be built without support for epoll family of system calls. config SIGNALFD bool "Enable signalfd() system call" if EXPERT default y help Enable the signalfd() system call that allows to receive signals on a file descriptor. If unsure, say Y. config TIMERFD bool "Enable timerfd() system call" if EXPERT default y help Enable the timerfd() system call that allows to receive timer events on a file descriptor. If unsure, say Y. config EVENTFD bool "Enable eventfd() system call" if EXPERT default y help Enable the eventfd() system call that allows to receive both kernel notification (ie. KAIO) or userspace notifications. If unsure, say Y. config SHMEM bool "Use full shmem filesystem" if EXPERT default y depends on MMU help The shmem is an internal filesystem used to manage shared memory. It is backed by swap and manages resource limits. It is also exported to userspace as tmpfs if TMPFS is enabled. Disabling this option replaces shmem and tmpfs with the much simpler ramfs code, which may be appropriate on small systems without swap. config AIO bool "Enable AIO support" if EXPERT default y help This option enables POSIX asynchronous I/O which may by used by some high performance threaded applications. Disabling this option saves about 7k. config IO_URING bool "Enable IO uring support" if EXPERT select IO_WQ default y help This option enables support for the io_uring interface, enabling applications to submit and complete IO through submission and completion rings that are shared between the kernel and application. config ADVISE_SYSCALLS bool "Enable madvise/fadvise syscalls" if EXPERT default y help This option enables the madvise and fadvise syscalls, used by applications to advise the kernel about their future memory or file usage, improving performance. If building an embedded system where no applications use these syscalls, you can disable this option to save space. config HAVE_ARCH_USERFAULTFD_WP bool help Arch has userfaultfd write protection support config HAVE_ARCH_USERFAULTFD_MINOR bool help Arch has userfaultfd minor fault support config MEMBARRIER bool "Enable membarrier() system call" if EXPERT default y help Enable the membarrier() system call that allows issuing memory barriers across all running threads, which can be used to distribute the cost of user-space memory barriers asymmetrically by transforming pairs of memory barriers into pairs consisting of membarrier() and a compiler barrier. If unsure, say Y. config KALLSYMS bool "Load all symbols for debugging/ksymoops" if EXPERT default y help Say Y here to let the kernel print out symbolic crash information and symbolic stack backtraces. This increases the size of the kernel somewhat, as all symbols have to be loaded into the kernel image. config KALLSYMS_ALL bool "Include all symbols in kallsyms" depends on DEBUG_KERNEL && KALLSYMS help Normally kallsyms only contains the symbols of functions for nicer OOPS messages and backtraces (i.e., symbols from the text and inittext sections). This is sufficient for most cases. And only in very rare cases (e.g., when a debugger is used) all symbols are required (e.g., names of variables from the data sections, etc). This option makes sure that all symbols are loaded into the kernel image (i.e., symbols from all sections) in cost of increased kernel size (depending on the kernel configuration, it may be 300KiB or something like this). Say N unless you really need all symbols. config KALLSYMS_ABSOLUTE_PERCPU bool depends on KALLSYMS default X86_64 && SMP config KALLSYMS_BASE_RELATIVE bool depends on KALLSYMS default !IA64 help Instead of emitting them as absolute values in the native word size, emit the symbol references in the kallsyms table as 32-bit entries, each containing a relative value in the range [base, base + U32_MAX] or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either an absolute value in the range [0, S32_MAX] or a relative value in the range [base, base + S32_MAX], where base is the lowest relative symbol address encountered in the image. On 64-bit builds, this reduces the size of the address table by 50%, but more importantly, it results in entries whose values are build time constants, and no relocation pass is required at runtime to fix up the entries based on the runtime load address of the kernel. # end of the "standard kernel features (expert users)" menu # syscall, maps, verifier config USERFAULTFD bool "Enable userfaultfd() system call" depends on MMU help Enable the userfaultfd() system call that allows to intercept and handle page faults in userland. config ARCH_HAS_MEMBARRIER_CALLBACKS bool config ARCH_HAS_MEMBARRIER_SYNC_CORE bool config KCMP bool "Enable kcmp() system call" if EXPERT help Enable the kernel resource comparison system call. It provides user-space with the ability to compare two processes to see if they share a common resource, such as a file descriptor or even virtual memory space. If unsure, say N. config RSEQ bool "Enable rseq() system call" if EXPERT default y depends on HAVE_RSEQ select MEMBARRIER help Enable the restartable sequences system call. It provides a user-space cache for the current CPU number value, which speeds up getting the current CPU number from user-space, as well as an ABI to speed up user-space operations on per-CPU data. If unsure, say Y. config DEBUG_RSEQ default n bool "Enabled debugging of rseq() system call" if EXPERT depends on RSEQ && DEBUG_KERNEL help Enable extra debugging checks for the rseq system call. If unsure, say N. config EMBEDDED bool "Embedded system" select EXPERT help This option should be enabled if compiling the kernel for an embedded system so certain expert options are available for configuration. config HAVE_PERF_EVENTS bool help See tools/perf/design.txt for details. config PERF_USE_VMALLOC bool help See tools/perf/design.txt for details config PC104 bool "PC/104 support" if EXPERT help Expose PC/104 form factor device drivers and options available for selection and configuration. Enable this option if your target machine has a PC/104 bus. menu "Kernel Performance Events And Counters" config PERF_EVENTS bool "Kernel performance events and counters" default y if PROFILING depends on HAVE_PERF_EVENTS select IRQ_WORK select SRCU help Enable kernel support for various performance events provided by software and hardware. Software events are supported either built-in or via the use of generic tracepoints. Most modern CPUs support performance events via performance counter registers. These registers count the number of certain types of hw events: such as instructions executed, cachemisses suffered, or branches mis-predicted - without slowing down the kernel or applications. These registers can also trigger interrupts when a threshold number of events have passed - and can thus be used to profile the code that runs on that CPU. The Linux Performance Event subsystem provides an abstraction of these software and hardware event capabilities, available via a system call and used by the "perf" utility in tools/perf/. It provides per task and per CPU counters, and it provides event capabilities on top of those. Say Y if unsure. config DEBUG_PERF_USE_VMALLOC default n bool "Debug: use vmalloc to back perf mmap() buffers" depends on PERF_EVENTS && DEBUG_KERNEL && !PPC select PERF_USE_VMALLOC help Use vmalloc memory to back perf mmap() buffers. Mostly useful for debugging the vmalloc code on platforms that don't require it. Say N if unsure. endmenu config VM_EVENT_COUNTERS default y bool "Enable VM event counters for /proc/vmstat" if EXPERT help VM event counters are needed for event counts to be shown. This option allows the disabling of the VM event counters on EXPERT systems. /proc/vmstat will only show page counts if VM event counters are disabled. config SLUB_DEBUG default y bool "Enable SLUB debugging support" if EXPERT depends on SLUB && SYSFS help SLUB has extensive debug support features. Disabling these can result in significant savings in code size. This also disables SLUB sysfs support. /sys/slab will not exist and there will be no support for cache validation etc. config COMPAT_BRK bool "Disable heap randomization" default y help Randomizing heap placement makes heap exploits harder, but it also breaks ancient binaries (including anything libc5 based). This option changes the bootup default to heap randomization disabled, and can be overridden at runtime by setting /proc/sys/kernel/randomize_va_space to 2. On non-ancient distros (post-2000 ones) N is usually a safe choice. choice prompt "Choose SLAB allocator" default SLUB help This option allows to select a slab allocator. config SLAB bool "SLAB" select HAVE_HARDENED_USERCOPY_ALLOCATOR help The regular slab allocator that is established and known to work well in all environments. It organizes cache hot objects in per cpu and per node queues. config SLUB bool "SLUB (Unqueued Allocator)" select HAVE_HARDENED_USERCOPY_ALLOCATOR help SLUB is a slab allocator that minimizes cache line usage instead of managing queues of cached objects (SLAB approach). Per cpu caching is realized using slabs of objects instead of queues of objects. SLUB can use memory efficiently and has enhanced diagnostics. SLUB is the default choice for a slab allocator. config SLOB depends on EXPERT bool "SLOB (Simple Allocator)" help SLOB replaces the stock allocator with a drastically simpler allocator. SLOB is generally more space efficient but does not perform as well on large systems. endchoice config SLAB_MERGE_DEFAULT bool "Allow slab caches to be merged" default y help For reduced kernel memory fragmentation, slab caches can be merged when they share the same size and other characteristics. This carries a risk of kernel heap overflows being able to overwrite objects from merged caches (and more easily control cache layout), which makes such heap attacks easier to exploit by attackers. By keeping caches unmerged, these kinds of exploits can usually only damage objects in the same cache. To disable merging at runtime, "slab_nomerge" can be passed on the kernel command line. config SLAB_FREELIST_RANDOM bool "Randomize slab freelist" depends on SLAB || SLUB help Randomizes the freelist order used on creating new pages. This security feature reduces the predictability of the kernel slab allocator against heap overflows. config SLAB_FREELIST_HARDENED bool "Harden slab freelist metadata" depends on SLAB || SLUB help Many kernel heap attacks try to target slab cache metadata and other infrastructure. This options makes minor performance sacrifices to harden the kernel slab allocator against common freelist exploit methods. Some slab implementations have more sanity-checking than others. This option is most effective with CONFIG_SLUB. config SHUFFLE_PAGE_ALLOCATOR bool "Page allocator randomization" default SLAB_FREELIST_RANDOM && ACPI_NUMA help Randomization of the page allocator improves the average utilization of a direct-mapped memory-side-cache. See section 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 6.2a specification for an example of how a platform advertises the presence of a memory-side-cache. There are also incidental security benefits as it reduces the predictability of page allocations to compliment SLAB_FREELIST_RANDOM, but the default granularity of shuffling on the "MAX_ORDER - 1" i.e, 10th order of pages is selected based on cache utilization benefits on x86. While the randomization improves cache utilization it may negatively impact workloads on platforms without a cache. For this reason, by default, the randomization is enabled only after runtime detection of a direct-mapped memory-side-cache. Otherwise, the randomization may be force enabled with the 'page_alloc.shuffle' kernel command line parameter. Say Y if unsure. config SLUB_CPU_PARTIAL default y depends on SLUB && SMP bool "SLUB per cpu partial cache" help Per cpu partial caches accelerate objects allocation and freeing that is local to a processor at the price of more indeterminism in the latency of the free. On overflow these caches will be cleared which requires the taking of locks that may cause latency spikes. Typically one would choose no for a realtime system. config MMAP_ALLOW_UNINITIALIZED bool "Allow mmapped anonymous memory to be uninitialized" depends on EXPERT && !MMU default n help Normally, and according to the Linux spec, anonymous memory obtained from mmap() has its contents cleared before it is passed to userspace. Enabling this config option allows you to request that mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus providing a huge performance boost. If this option is not enabled, then the flag will be ignored. This is taken advantage of by uClibc's malloc(), and also by ELF-FDPIC binfmt's brk and stack allocator. Because of the obvious security issues, this option should only be enabled on embedded devices where you control what is run in userspace. Since that isn't generally a problem on no-MMU systems, it is normally safe to say Y here. See Documentation/admin-guide/mm/nommu-mmap.rst for more information. config SYSTEM_DATA_VERIFICATION def_bool n select SYSTEM_TRUSTED_KEYRING select KEYS select CRYPTO select CRYPTO_RSA select ASYMMETRIC_KEY_TYPE select ASYMMETRIC_PUBLIC_KEY_SUBTYPE select ASN1 select OID_REGISTRY select X509_CERTIFICATE_PARSER select PKCS7_MESSAGE_PARSER help Provide PKCS#7 message verification using the contents of the system trusted keyring to provide public keys. This then can be used for module verification, kexec image verification and firmware blob verification. config PROFILING bool "Profiling support" help Say Y here to enable the extended profiling support mechanisms used by profilers. # # Place an empty function call at each tracepoint site. Can be # dynamically changed for a probe function. # config TRACEPOINTS bool endmenu # General setup source "arch/Kconfig" config RT_MUTEXES bool config BASE_SMALL int default 0 if BASE_FULL default 1 if !BASE_FULL config MODULE_SIG_FORMAT def_bool n select SYSTEM_DATA_VERIFICATION menuconfig MODULES bool "Enable loadable module support" modules help Kernel modules are small pieces of compiled code which can be inserted in the running kernel, rather than being permanently built into the kernel. You use the "modprobe" tool to add (and sometimes remove) them. If you say Y here, many parts of the kernel can be built as modules (by answering M instead of Y where indicated): this is most useful for infrequently used options which are not required for booting. For more information, see the man pages for modprobe, lsmod, modinfo, insmod and rmmod. If you say Y here, you will need to run "make modules_install" to put the modules under /lib/modules/ where modprobe can find them (you may need to be root to do this). If unsure, say Y. if MODULES config MODULE_FORCE_LOAD bool "Forced module loading" default n help Allow loading of modules without version information (ie. modprobe --force). Forced module loading sets the 'F' (forced) taint flag and is usually a really bad idea. config MODULE_UNLOAD bool "Module unloading" help Without this option you will not be able to unload any modules (note that some modules may not be unloadable anyway), which makes your kernel smaller, faster and simpler. If unsure, say Y. config MODULE_FORCE_UNLOAD bool "Forced module unloading" depends on MODULE_UNLOAD help This option allows you to force a module to unload, even if the kernel believes it is unsafe: the kernel will remove the module without waiting for anyone to stop using it (using the -f option to rmmod). This is mainly for kernel developers and desperate users. If unsure, say N. config MODVERSIONS bool "Module versioning support" help Usually, you have to use modules compiled with your kernel. Saying Y here makes it sometimes possible to use modules compiled for different kernels, by adding enough information to the modules to (hopefully) spot any changes which would make them incompatible with the kernel you are running. If unsure, say N. config ASM_MODVERSIONS bool default HAVE_ASM_MODVERSIONS && MODVERSIONS help This enables module versioning for exported symbols also from assembly. This can be enabled only when the target architecture supports it. config MODULE_REL_CRCS bool depends on MODVERSIONS config MODULE_SRCVERSION_ALL bool "Source checksum for all modules" help Modules which contain a MODULE_VERSION get an extra "srcversion" field inserted into their modinfo section, which contains a sum of the source files which made it. This helps maintainers see exactly which source was used to build a module (since others sometimes change the module source without updating the version). With this option, such a "srcversion" field will be created for all modules. If unsure, say N. config MODULE_SIG bool "Module signature verification" select MODULE_SIG_FORMAT help Check modules for valid signatures upon load: the signature is simply appended to the module. For more information see <file:Documentation/admin-guide/module-signing.rst>. Note that this option adds the OpenSSL development packages as a kernel build dependency so that the signing tool can use its crypto library. You should enable this option if you wish to use either CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via another LSM - otherwise unsigned modules will be loadable regardless of the lockdown policy. !!!WARNING!!! If you enable this option, you MUST make sure that the module DOES NOT get stripped after being signed. This includes the debuginfo strip done by some packagers (such as rpmbuild) and inclusion into an initramfs that wants the module size reduced. config MODULE_SIG_FORCE bool "Require modules to be validly signed" depends on MODULE_SIG help Reject unsigned modules or signed modules for which we don't have a key. Without this, such modules will simply taint the kernel. config MODULE_SIG_ALL bool "Automatically sign all modules" default y depends on MODULE_SIG || IMA_APPRAISE_MODSIG help Sign all modules during make modules_install. Without this option, modules must be signed manually, using the scripts/sign-file tool. comment "Do not forget to sign required modules with scripts/sign-file" depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL choice prompt "Which hash algorithm should modules be signed with?" depends on MODULE_SIG || IMA_APPRAISE_MODSIG help This determines which sort of hashing algorithm will be used during signature generation. This algorithm _must_ be built into the kernel directly so that signature verification can take place. It is not possible to load a signed module containing the algorithm to check the signature on that module. config MODULE_SIG_SHA1 bool "Sign modules with SHA-1" select CRYPTO_SHA1 config MODULE_SIG_SHA224 bool "Sign modules with SHA-224" select CRYPTO_SHA256 config MODULE_SIG_SHA256 bool "Sign modules with SHA-256" select CRYPTO_SHA256 config MODULE_SIG_SHA384 bool "Sign modules with SHA-384" select CRYPTO_SHA512 config MODULE_SIG_SHA512 bool "Sign modules with SHA-512" select CRYPTO_SHA512 endchoice config MODULE_SIG_HASH string depends on MODULE_SIG || IMA_APPRAISE_MODSIG default "sha1" if MODULE_SIG_SHA1 default "sha224" if MODULE_SIG_SHA224 default "sha256" if MODULE_SIG_SHA256 default "sha384" if MODULE_SIG_SHA384 default "sha512" if MODULE_SIG_SHA512 choice prompt "Module compression mode" help This option allows you to choose the algorithm which will be used to compress modules when 'make modules_install' is run. (or, you can choose to not compress modules at all.) External modules will also be compressed in the same way during the installation. For modules inside an initrd or initramfs, it's more efficient to compress the whole initrd or initramfs instead. This is fully compatible with signed modules. Please note that the tool used to load modules needs to support the corresponding algorithm. module-init-tools MAY support gzip, and kmod MAY support gzip, xz and zstd. Your build system needs to provide the appropriate compression tool to compress the modules. If in doubt, select 'None'. config MODULE_COMPRESS_NONE bool "None" help Do not compress modules. The installed modules are suffixed with .ko. config MODULE_COMPRESS_GZIP bool "GZIP" help Compress modules with GZIP. The installed modules are suffixed with .ko.gz. config MODULE_COMPRESS_XZ bool "XZ" help Compress modules with XZ. The installed modules are suffixed with .ko.xz. config MODULE_COMPRESS_ZSTD bool "ZSTD" help Compress modules with ZSTD. The installed modules are suffixed with .ko.zst. endchoice config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS bool "Allow loading of modules with missing namespace imports" help Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in a namespace. A module that makes use of a symbol exported with such a namespace is required to import the namespace via MODULE_IMPORT_NS(). There is no technical reason to enforce correct namespace imports, but it creates consistency between symbols defining namespaces and users importing namespaces they make use of. This option relaxes this requirement and lifts the enforcement when loading a module. If unsure, say N. config MODPROBE_PATH string "Path to modprobe binary" default "/sbin/modprobe" help When kernel code requests a module, it does so by calling the "modprobe" userspace utility. This option allows you to set the path where that binary is found. This can be changed at runtime via the sysctl file /proc/sys/kernel/modprobe. Setting this to the empty string removes the kernel's ability to request modules (but userspace can still load modules explicitly). config TRIM_UNUSED_KSYMS bool "Trim unused exported kernel symbols" if EXPERT depends on !COMPILE_TEST help The kernel and some modules make many symbols available for other modules to use via EXPORT_SYMBOL() and variants. Depending on the set of modules being selected in your kernel configuration, many of those exported symbols might never be used. This option allows for unused exported symbols to be dropped from the build. In turn, this provides the compiler more opportunities (especially when using LTO) for optimizing the code and reducing binary size. This might have some security advantages as well. If unsure, or if you need to build out-of-tree modules, say N. config UNUSED_KSYMS_WHITELIST string "Whitelist of symbols to keep in ksymtab" depends on TRIM_UNUSED_KSYMS help By default, all unused exported symbols will be un-exported from the build when TRIM_UNUSED_KSYMS is selected. UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept exported at all times, even in absence of in-tree users. The value to set here is the path to a text file containing the list of symbols, one per line. The path can be absolute, or relative to the kernel source tree. endif # MODULES config MODULES_TREE_LOOKUP def_bool y depends on PERF_EVENTS || TRACING || CFI_CLANG config INIT_ALL_POSSIBLE bool help Back when each arch used to define their own cpu_online_mask and cpu_possible_mask, some of them chose to initialize cpu_possible_mask with all 1s, and others with all 0s. When they were centralised, it was better to provide this option than to break all the archs and have several arch maintainers pursuing me down dark alleys. source "block/Kconfig" config PREEMPT_NOTIFIERS bool config PADATA depends on SMP bool config ASN1 tristate help Build a simple ASN.1 grammar compiler that produces a bytecode output that can be interpreted by the ASN.1 stream decoder and used to inform it as to what tags are to be expected in a stream and what functions to call on what tags. source "kernel/Kconfig.locks" config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE bool config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE bool # It may be useful for an architecture to override the definitions of the # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h> # and the COMPAT_ variants in <linux/compat.h>, in particular to use a # different calling convention for syscalls. They can also override the # macros for not-implemented syscalls in kernel/sys_ni.c and # kernel/time/posix-stubs.c. All these overrides need to be available in # <asm/syscall_wrapper.h>. config ARCH_HAS_SYSCALL_WRAPPER def_bool n