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linux/lib/Kconfig
Linus Torvalds 5d272dd1b3 cpumask: limit FORCE_NR_CPUS to just the UP case 
Hardcoding the number of CPUs at compile time does improve code
generation, but if you get it wrong the result will be confusion.

We already limited this earlier to only "experts" (see commit
fe5759d5bf "cpumask: limit visibility of FORCE_NR_CPUS"), but with
distro kernel configs often having EXPERT enabled, that turns out to not
be much of a limit.

To quote the philosophers at Disney: "Everyone can be an expert. And
when everyone's an expert, no one will be".

There's a runtime warning if you then set nr_cpus to anything but the
forced number, but apparently that can be ignored too [1] and by then
it's pretty much too late anyway.

If we had some real way to limit this to "embedded only", maybe it would
be worth it, but let's see if anybody even notices that the option is
gone.  We need to simplify kernel configuration anyway.

Link: https://lore.kernel.org/all/20240618105036.208a8860@rorschach.local.home/ [1]
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-06-18 09:00:04 -07:00

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# SPDX-License-Identifier: GPL-2.0-only
#
# Library configuration
#
config BINARY_PRINTF
def_bool n
menu "Library routines"
config RAID6_PQ
tristate
config RAID6_PQ_BENCHMARK
bool "Automatically choose fastest RAID6 PQ functions"
depends on RAID6_PQ
default y
help
Benchmark all available RAID6 PQ functions on init and choose the
fastest one.
config LINEAR_RANGES
tristate
config PACKING
bool "Generic bitfield packing and unpacking"
select BITREVERSE
default n
help
This option provides the packing() helper function, which permits
converting bitfields between a CPU-usable representation and a
memory representation that can have any combination of these quirks:
- Is little endian (bytes are reversed within a 32-bit group)
- The least-significant 32-bit word comes first (within a 64-bit
group)
- The most significant bit of a byte is at its right (bit 0 of a
register description is numerically 2^7).
Drivers may use these helpers to match the bit indices as described
in the data sheets of the peripherals they are in control of.
When in doubt, say N.
config BITREVERSE
tristate
config HAVE_ARCH_BITREVERSE
bool
default n
help
This option enables the use of hardware bit-reversal instructions on
architectures which support such operations.
config ARCH_HAS_STRNCPY_FROM_USER
bool
config ARCH_HAS_STRNLEN_USER
bool
config GENERIC_STRNCPY_FROM_USER
def_bool !ARCH_HAS_STRNCPY_FROM_USER
config GENERIC_STRNLEN_USER
def_bool !ARCH_HAS_STRNLEN_USER
config GENERIC_NET_UTILS
bool
source "lib/math/Kconfig"
config NO_GENERIC_PCI_IOPORT_MAP
bool
config GENERIC_IOMAP
bool
select GENERIC_PCI_IOMAP
config STMP_DEVICE
bool
config ARCH_USE_CMPXCHG_LOCKREF
bool
config ARCH_HAS_FAST_MULTIPLIER
bool
config ARCH_USE_SYM_ANNOTATIONS
bool
config INDIRECT_PIO
bool "Access I/O in non-MMIO mode"
depends on ARM64
depends on HAS_IOPORT
help
On some platforms where no separate I/O space exists, there are I/O
hosts which can not be accessed in MMIO mode. Using the logical PIO
mechanism, the host-local I/O resource can be mapped into system
logic PIO space shared with MMIO hosts, such as PCI/PCIe, then the
system can access the I/O devices with the mapped-logic PIO through
I/O accessors.
This way has relatively little I/O performance cost. Please make
sure your devices really need this configure item enabled.
When in doubt, say N.
config INDIRECT_IOMEM
bool
help
This is selected by other options/architectures to provide the
emulated iomem accessors.
config INDIRECT_IOMEM_FALLBACK
bool
depends on INDIRECT_IOMEM
help
If INDIRECT_IOMEM is selected, this enables falling back to plain
mmio accesses when the IO memory address is not a registered
emulated region.
config TRACE_MMIO_ACCESS
bool "Register read/write tracing"
depends on TRACING && ARCH_HAVE_TRACE_MMIO_ACCESS
help
Create tracepoints for MMIO read/write operations. These trace events
can be used for logging all MMIO read/write operations.
source "lib/crypto/Kconfig"
config CRC_CCITT
tristate "CRC-CCITT functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC-CCITT functions, but a module built outside
the kernel tree does. Such modules that use library CRC-CCITT
functions require M here.
config CRC16
tristate "CRC16 functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC16 functions, but a module built outside
the kernel tree does. Such modules that use library CRC16
functions require M here.
config CRC_T10DIF
tristate "CRC calculation for the T10 Data Integrity Field"
select CRYPTO
select CRYPTO_CRCT10DIF
help
This option is only needed if a module that's not in the
kernel tree needs to calculate CRC checks for use with the
SCSI data integrity subsystem.
config CRC64_ROCKSOFT
tristate "CRC calculation for the Rocksoft model CRC64"
select CRC64
select CRYPTO
select CRYPTO_CRC64_ROCKSOFT
help
This option provides a CRC64 API to a registered crypto driver.
This is used with the block layer's data integrity subsystem.
config CRC_ITU_T
tristate "CRC ITU-T V.41 functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC ITU-T V.41 functions, but a module built outside
the kernel tree does. Such modules that use library CRC ITU-T V.41
functions require M here.
config CRC32
tristate "CRC32/CRC32c functions"
default y
select BITREVERSE
help
This option is provided for the case where no in-kernel-tree
modules require CRC32/CRC32c functions, but a module built outside
the kernel tree does. Such modules that use library CRC32/CRC32c
functions require M here.
config CRC32_SELFTEST
tristate "CRC32 perform self test on init"
depends on CRC32
help
This option enables the CRC32 library functions to perform a
self test on initialization. The self test computes crc32_le
and crc32_be over byte strings with random alignment and length
and computes the total elapsed time and number of bytes processed.
choice
prompt "CRC32 implementation"
depends on CRC32
default CRC32_SLICEBY8
help
This option allows a kernel builder to override the default choice
of CRC32 algorithm. Choose the default ("slice by 8") unless you
know that you need one of the others.
config CRC32_SLICEBY8
bool "Slice by 8 bytes"
help
Calculate checksum 8 bytes at a time with a clever slicing algorithm.
This is the fastest algorithm, but comes with a 8KiB lookup table.
Most modern processors have enough cache to hold this table without
thrashing the cache.
This is the default implementation choice. Choose this one unless
you have a good reason not to.
config CRC32_SLICEBY4
bool "Slice by 4 bytes"
help
Calculate checksum 4 bytes at a time with a clever slicing algorithm.
This is a bit slower than slice by 8, but has a smaller 4KiB lookup
table.
Only choose this option if you know what you are doing.
config CRC32_SARWATE
bool "Sarwate's Algorithm (one byte at a time)"
help
Calculate checksum a byte at a time using Sarwate's algorithm. This
is not particularly fast, but has a small 256 byte lookup table.
Only choose this option if you know what you are doing.
config CRC32_BIT
bool "Classic Algorithm (one bit at a time)"
help
Calculate checksum one bit at a time. This is VERY slow, but has
no lookup table. This is provided as a debugging option.
Only choose this option if you are debugging crc32.
endchoice
config CRC64
tristate "CRC64 functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC64 functions, but a module built outside
the kernel tree does. Such modules that use library CRC64
functions require M here.
config CRC4
tristate "CRC4 functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC4 functions, but a module built outside
the kernel tree does. Such modules that use library CRC4
functions require M here.
config CRC7
tristate "CRC7 functions"
help
This option is provided for the case where no in-kernel-tree
modules require CRC7 functions, but a module built outside
the kernel tree does. Such modules that use library CRC7
functions require M here.
config LIBCRC32C
tristate "CRC32c (Castagnoli, et al) Cyclic Redundancy-Check"
select CRYPTO
select CRYPTO_CRC32C
help
This option is provided for the case where no in-kernel-tree
modules require CRC32c functions, but a module built outside the
kernel tree does. Such modules that use library CRC32c functions
require M here. See Castagnoli93.
Module will be libcrc32c.
config CRC8
tristate "CRC8 function"
help
This option provides CRC8 function. Drivers may select this
when they need to do cyclic redundancy check according CRC8
algorithm. Module will be called crc8.
config XXHASH
tristate
config AUDIT_GENERIC
bool
depends on AUDIT && !AUDIT_ARCH
default y
config AUDIT_ARCH_COMPAT_GENERIC
bool
default n
config AUDIT_COMPAT_GENERIC
bool
depends on AUDIT_GENERIC && AUDIT_ARCH_COMPAT_GENERIC && COMPAT
default y
config RANDOM32_SELFTEST
bool "PRNG perform self test on init"
help
This option enables the 32 bit PRNG library functions to perform a
self test on initialization.
#
# compression support is select'ed if needed
#
config 842_COMPRESS
select CRC32
tristate
config 842_DECOMPRESS
select CRC32
tristate
config ZLIB_INFLATE
tristate
config ZLIB_DEFLATE
tristate
select BITREVERSE
config ZLIB_DFLTCC
def_bool y
depends on S390
prompt "Enable s390x DEFLATE CONVERSION CALL support for kernel zlib"
help
Enable s390x hardware support for zlib in the kernel.
config LZO_COMPRESS
tristate
config LZO_DECOMPRESS
tristate
config LZ4_COMPRESS
tristate
config LZ4HC_COMPRESS
tristate
config LZ4_DECOMPRESS
tristate
config ZSTD_COMMON
select XXHASH
tristate
config ZSTD_COMPRESS
select ZSTD_COMMON
tristate
config ZSTD_DECOMPRESS
select ZSTD_COMMON
tristate
source "lib/xz/Kconfig"
#
# These all provide a common interface (hence the apparent duplication with
# ZLIB_INFLATE; DECOMPRESS_GZIP is just a wrapper.)
#
config DECOMPRESS_GZIP
select ZLIB_INFLATE
tristate
config DECOMPRESS_BZIP2
tristate
config DECOMPRESS_LZMA
tristate
config DECOMPRESS_XZ
select XZ_DEC
tristate
config DECOMPRESS_LZO
select LZO_DECOMPRESS
tristate
config DECOMPRESS_LZ4
select LZ4_DECOMPRESS
tristate
config DECOMPRESS_ZSTD
select ZSTD_DECOMPRESS
tristate
#
# Generic allocator support is selected if needed
#
config GENERIC_ALLOCATOR
bool
#
# reed solomon support is select'ed if needed
#
config REED_SOLOMON
tristate
config REED_SOLOMON_ENC8
bool
config REED_SOLOMON_DEC8
bool
config REED_SOLOMON_ENC16
bool
config REED_SOLOMON_DEC16
bool
#
# BCH support is selected if needed
#
config BCH
tristate
select BITREVERSE
config BCH_CONST_PARAMS
bool
help
Drivers may select this option to force specific constant
values for parameters 'm' (Galois field order) and 't'
(error correction capability). Those specific values must
be set by declaring default values for symbols BCH_CONST_M
and BCH_CONST_T.
Doing so will enable extra compiler optimizations,
improving encoding and decoding performance up to 2x for
usual (m,t) values (typically such that m*t < 200).
When this option is selected, the BCH library supports
only a single (m,t) configuration. This is mainly useful
for NAND flash board drivers requiring known, fixed BCH
parameters.
config BCH_CONST_M
int
range 5 15
help
Constant value for Galois field order 'm'. If 'k' is the
number of data bits to protect, 'm' should be chosen such
that (k + m*t) <= 2**m - 1.
Drivers should declare a default value for this symbol if
they select option BCH_CONST_PARAMS.
config BCH_CONST_T
int
help
Constant value for error correction capability in bits 't'.
Drivers should declare a default value for this symbol if
they select option BCH_CONST_PARAMS.
#
# Textsearch support is select'ed if needed
#
config TEXTSEARCH
bool
config TEXTSEARCH_KMP
tristate
config TEXTSEARCH_BM
tristate
config TEXTSEARCH_FSM
tristate
config BTREE
bool
config INTERVAL_TREE
bool
help
Simple, embeddable, interval-tree. Can find the start of an
overlapping range in log(n) time and then iterate over all
overlapping nodes. The algorithm is implemented as an
augmented rbtree.
See:
Documentation/core-api/rbtree.rst
for more information.
config INTERVAL_TREE_SPAN_ITER
bool
depends on INTERVAL_TREE
config XARRAY_MULTI
bool
help
Support entries which occupy multiple consecutive indices in the
XArray.
config ASSOCIATIVE_ARRAY
bool
help
Generic associative array. Can be searched and iterated over whilst
it is being modified. It is also reasonably quick to search and
modify. The algorithms are non-recursive, and the trees are highly
capacious.
See:
Documentation/core-api/assoc_array.rst
for more information.
config CLOSURES
bool
config HAS_IOMEM
bool
depends on !NO_IOMEM
default y
config HAS_IOPORT
bool
config HAS_IOPORT_MAP
bool
depends on HAS_IOMEM && !NO_IOPORT_MAP
default y
source "kernel/dma/Kconfig"
config SGL_ALLOC
bool
default n
config IOMMU_HELPER
bool
config CHECK_SIGNATURE
bool
config CPUMASK_OFFSTACK
bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
help
Use dynamic allocation for cpumask_var_t, instead of putting
them on the stack. This is a bit more expensive, but avoids
stack overflow.
config FORCE_NR_CPUS
def_bool !SMP
config CPU_RMAP
bool
depends on SMP
config DQL
bool
config GLOB
bool
# This actually supports modular compilation, but the module overhead
# is ridiculous for the amount of code involved. Until an out-of-tree
# driver asks for it, we'll just link it directly it into the kernel
# when required. Since we're ignoring out-of-tree users, there's also
# no need bother prompting for a manual decision:
# prompt "glob_match() function"
help
This option provides a glob_match function for performing
simple text pattern matching. It originated in the ATA code
to blacklist particular drive models, but other device drivers
may need similar functionality.
All drivers in the Linux kernel tree that require this function
should automatically select this option. Say N unless you
are compiling an out-of tree driver which tells you that it
depends on this.
config GLOB_SELFTEST
tristate "glob self-test on init"
depends on GLOB
help
This option enables a simple self-test of the glob_match
function on startup. It is primarily useful for people
working on the code to ensure they haven't introduced any
regressions.
It only adds a little bit of code and slows kernel boot (or
module load) by a small amount, so you're welcome to play with
it, but you probably don't need it.
#
# Netlink attribute parsing support is select'ed if needed
#
config NLATTR
bool
#
# Generic 64-bit atomic support is selected if needed
#
config GENERIC_ATOMIC64
bool
config LRU_CACHE
tristate
config CLZ_TAB
bool
config IRQ_POLL
bool "IRQ polling library"
help
Helper library to poll interrupt mitigation using polling.
config MPILIB
tristate
select CLZ_TAB
help
Multiprecision maths library from GnuPG.
It is used to implement RSA digital signature verification,
which is used by IMA/EVM digital signature extension.
config SIGNATURE
tristate
depends on KEYS
select CRYPTO
select CRYPTO_SHA1
select MPILIB
help
Digital signature verification. Currently only RSA is supported.
Implementation is done using GnuPG MPI library
config DIMLIB
tristate
help
Dynamic Interrupt Moderation library.
Implements an algorithm for dynamically changing CQ moderation values
according to run time performance.
#
# libfdt files, only selected if needed.
#
config LIBFDT
bool
config OID_REGISTRY
tristate
help
Enable fast lookup object identifier registry.
config UCS2_STRING
tristate
#
# generic vdso
#
source "lib/vdso/Kconfig"
source "lib/fonts/Kconfig"
config SG_SPLIT
def_bool n
help
Provides a helper to split scatterlists into chunks, each chunk being
a scatterlist. This should be selected by a driver or an API which
whishes to split a scatterlist amongst multiple DMA channels.
config SG_POOL
def_bool n
help
Provides a helper to allocate chained scatterlists. This should be
selected by a driver or an API which whishes to allocate chained
scatterlist.
#
# sg chaining option
#
config ARCH_NO_SG_CHAIN
def_bool n
config ARCH_HAS_PMEM_API
bool
config MEMREGION
bool
config ARCH_HAS_CPU_CACHE_INVALIDATE_MEMREGION
bool
config ARCH_HAS_MEMREMAP_COMPAT_ALIGN
bool
# use memcpy to implement user copies for nommu architectures
config UACCESS_MEMCPY
bool
config ARCH_HAS_UACCESS_FLUSHCACHE
bool
# arch has a concept of a recoverable synchronous exception due to a
# memory-read error like x86 machine-check or ARM data-abort, and
# implements copy_mc_to_{user,kernel} to abort and report
# 'bytes-transferred' if that exception fires when accessing the source
# buffer.
config ARCH_HAS_COPY_MC
bool
# Temporary. Goes away when all archs are cleaned up
config ARCH_STACKWALK
bool
config STACKDEPOT
bool
select STACKTRACE
help
Stack depot: stack trace storage that avoids duplication
config STACKDEPOT_ALWAYS_INIT
bool
select STACKDEPOT
help
Always initialize stack depot during early boot
config STACKDEPOT_MAX_FRAMES
int "Maximum number of frames in trace saved in stack depot"
range 1 256
default 64
depends on STACKDEPOT
config REF_TRACKER
bool
depends on STACKTRACE_SUPPORT
select STACKDEPOT
config SBITMAP
bool
config PARMAN
tristate "parman" if COMPILE_TEST
config OBJAGG
tristate "objagg" if COMPILE_TEST
config LWQ_TEST
bool "Boot-time test for lwq queuing"
help
Run boot-time test of light-weight queuing.
endmenu
config GENERIC_IOREMAP
bool
config GENERIC_LIB_ASHLDI3
bool
config GENERIC_LIB_ASHRDI3
bool
config GENERIC_LIB_LSHRDI3
bool
config GENERIC_LIB_MULDI3
bool
config GENERIC_LIB_CMPDI2
bool
config GENERIC_LIB_UCMPDI2
bool
config GENERIC_LIB_DEVMEM_IS_ALLOWED
bool
config PLDMFW
bool
default n
config ASN1_ENCODER
tristate
config POLYNOMIAL
tristate
config FIRMWARE_TABLE
bool
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