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Kconfig
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# 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 RUSTC_VERSION
int
default $(rustc-version)
help
It does not depend on `RUST` since that one may need to use the version
in a `depends on`.
config RUST_IS_AVAILABLE
def_bool $(success,$(srctree)/scripts/rust_is_available.sh)
help
This shows whether a suitable Rust toolchain is available (found).
Please see Documentation/rust/quick-start.rst for instructions on how
to satisfy the build requirements of Rust support.
In particular, the Makefile target 'rustavailable' is useful to check
why the Rust toolchain is not being detected.
config RUSTC_LLVM_VERSION
int
default $(rustc-llvm-version)
config CC_CAN_LINK
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
config CC_CAN_LINK_STATIC
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
# Fixed in GCC 14, 13.3, 12.4 and 11.5
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
config GCC_ASM_GOTO_OUTPUT_BROKEN
bool
depends on CC_IS_GCC
default y if GCC_VERSION < 110500
default y if GCC_VERSION >= 120000 && GCC_VERSION < 120400
default y if GCC_VERSION >= 130000 && GCC_VERSION < 130300
config CC_HAS_ASM_GOTO_OUTPUT
def_bool y
depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
depends on $(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 CC_HAS_COUNTED_BY
# TODO: when gcc 15 is released remove the build test and add
# a gcc version check
def_bool $(success,echo 'struct flex { int count; int array[] __attribute__((__counted_by__(count))); };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
# clang needs to be at least 19.1.3 to avoid __bdos miscalculations
# https://github.com/llvm/llvm-project/pull/110497
# https://github.com/llvm/llvm-project/pull/112636
depends on !(CC_IS_CLANG && CLANG_VERSION < 190103)
config PAHOLE_VERSION
int
default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
config CONSTRUCTORS
bool
config IRQ_WORK
def_bool y if SMP
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' (for C) and '-Dwarnings' (for Rust) flags
to enforce that rule by default. Certain warnings from other tools
such as the linker may be upgraded to errors with this option as
well.
However, if you have a new (or very old) compiler or linker 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 12 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 POLLY_CLANG
bool "Use Clang Polly optimizations"
depends on CC_IS_CLANG && $(cc-option,-mllvm -polly -fplugin=LLVMPolly.so
depends on !COMPILE_TEST
help
This option enables Clang's polyhedral loop optimizer known as
Polly. Polly is able to optimize various loops throughout the
kernel for cache locality. This requires a Clang toolchain
compiled with support for Polly. More information can be found
from Polly's website:
https://polly.llvm.org
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, ARM64, RISC-V, big endian 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.
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 SYSVIPC_COMPAT
def_bool y
depends on COMPAT && SYSVIPC
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/core-api/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 (for libc5 and earlier)"
default ALPHA || M68K || SPARC
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
# 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_USER
depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
depends on GENERIC_CLOCKEVENTS
select VIRT_CPU_ACCOUNTING
select CONTEXT_TRACKING_USER
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_HW_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 HW pressure accounting in the
scheduler. HW pressure is the value conveyed to the scheduler
that reflects the reduction in CPU compute capacity resulted from
HW throttling. HW throttling occurs when the performance of
a CPU is capped due to high operating temperatures as an example.
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_update_hw_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"
select KERNFS
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 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
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 0 if BASE_SMALL
default 12
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_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
config CC_IMPLICIT_FALLTHROUGH
string
default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
# Currently, disable gcc-10+ array-bounds globally.
# It's still broken in gcc-13, so no upper bound yet.
config GCC10_NO_ARRAY_BOUNDS
def_bool y
config CC_NO_ARRAY_BOUNDS
bool
default y if CC_IS_GCC && GCC_VERSION >= 90000 && GCC10_NO_ARRAY_BOUNDS
# Currently, disable -Wstringop-overflow for GCC globally.
config GCC_NO_STRINGOP_OVERFLOW
def_bool y
config CC_NO_STRINGOP_OVERFLOW
bool
default y if CC_IS_GCC && GCC_NO_STRINGOP_OVERFLOW
config CC_STRINGOP_OVERFLOW
bool
default y if CC_IS_GCC && !CC_NO_STRINGOP_OVERFLOW
#
# 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 && !PREEMPT_RT
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.
config SLAB_OBJ_EXT
bool
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 CGROUP_FAVOR_DYNMODS
bool "Favor dynamic modification latency reduction by default"
help
This option enables the "favordynmods" mount option by default
which reduces the latencies of dynamic cgroup modifications such
as task migrations and controller on/offs at the cost of making
hot path operations such as forks and exits more expensive.
Say N if unsure.
config MEMCG