kernel/Kconfig

# Kernel configuration options

# Copyright (c) 2014-2015 Wind River Systems, Inc.
# SPDX-License-Identifier: Apache-2.0

menu "General Kernel Options"

module = KERNEL
module-str = kernel
source "subsys/logging/Kconfig.template.log_config"

config MULTITHREADING
	bool "Multi-threading (DEPRECATED)"
	default y
	help
	  Disabling this option is DEPRECATED.

	  If disabled, only the main thread is available, so a main() function
	  must be provided. Interrupts are available. Kernel objects will most
	  probably not behave as expected, especially with regards to pending,
	  since the main thread cannot pend, it being the only thread in the
	  system.

	  Many drivers and subsystems will not work with this option
	  set to 'n'; disable only when you REALLY know what you are
	  doing.

if !MULTITHREADING
comment "*** WARNING ***"
comment "Single threaded mode (MULTITHREADING option disabled) is deprecated"
endif

config NUM_COOP_PRIORITIES
	int "Number of coop priorities" if MULTITHREADING
	default 1 if !MULTITHREADING
	default 16
	range 0 128
	help
	  Number of cooperative priorities configured in the system. Gives access
	  to priorities:

		K_PRIO_COOP(0) to K_PRIO_COOP(CONFIG_NUM_COOP_PRIORITIES - 1)

	  or seen another way, priorities:

		-CONFIG_NUM_COOP_PRIORITIES to -1

	  This can be set to zero to disable cooperative scheduling. Cooperative
	  threads always preempt preemptible threads.

	  Each priority requires an extra 8 bytes of RAM. Each set of 32 extra
	  total priorities require an extra 4 bytes and add one possible
	  iteration to loops that search for the next thread to run.

	  The total number of priorities is

	   NUM_COOP_PRIORITIES + NUM_PREEMPT_PRIORITIES + 1

	  The extra one is for the idle thread, which must run at the lowest
	  priority, and be the only thread at that priority.

config NUM_PREEMPT_PRIORITIES
	int "Number of preemptible priorities" if MULTITHREADING
	default 0 if !MULTITHREADING
	default 15
	range 0 128
	help
	  Number of preemptible priorities available in the system. Gives access
	  to priorities 0 to CONFIG_NUM_PREEMPT_PRIORITIES - 1.

	  This can be set to 0 to disable preemptible scheduling.

	  Each priority requires an extra 8 bytes of RAM. Each set of 32 extra
	  total priorities require an extra 4 bytes and add one possible
	  iteration to loops that search for the next thread to run.

	  The total number of priorities is

	   NUM_COOP_PRIORITIES + NUM_PREEMPT_PRIORITIES + 1

	  The extra one is for the idle thread, which must run at the lowest
	  priority, and be the only thread at that priority.

config MAIN_THREAD_PRIORITY
	int "Priority of initialization/main thread"
	default -2 if !PREEMPT_ENABLED
	default 0
	help
	  Priority at which the initialization thread runs, including the start
	  of the main() function. main() can then change its priority if desired.

config COOP_ENABLED
	def_bool (NUM_COOP_PRIORITIES != 0)

config PREEMPT_ENABLED
	def_bool (NUM_PREEMPT_PRIORITIES != 0)

config PRIORITY_CEILING
	int "Priority inheritance ceiling"
	default 0

config NUM_METAIRQ_PRIORITIES
	int "Number of very-high priority 'preemptor' threads"
	default 0
	help
	  This defines a set of priorities at the (numerically) lowest
	  end of the range which have "meta-irq" behavior.  Runnable
	  threads at these priorities will always be scheduled before
	  threads at lower priorities, EVEN IF those threads are
	  otherwise cooperative and/or have taken a scheduler lock.
	  Making such a thread runnable in any way thus has the effect
	  of "interrupting" the current task and running the meta-irq
	  thread synchronously, like an exception or system call.  The
	  intent is to use these priorities to implement "interrupt
	  bottom half" or "tasklet" behavior, allowing driver
	  subsystems to return from interrupt context but be guaranteed
	  that user code will not be executed (on the current CPU)
	  until the remaining work is finished.  As this breaks the
	  "promise" of non-preemptibility granted by the current API
	  for cooperative threads, this tool probably shouldn't be used
	  from application code.

config SCHED_DEADLINE
	bool "Enable earliest-deadline-first scheduling"
	help
	  This enables a simple "earliest deadline first" scheduling
	  mode where threads can set "deadline" deltas measured in
	  k_cycle_get_32() units.  Priority decisions within (!!) a
	  single priority will choose the next expiring deadline and
	  not simply the least recently added thread.

config SCHED_CPU_MASK
	bool "Enable CPU mask affinity/pinning API"
	depends on SCHED_DUMB
	help
	  When true, the application will have access to the
	  k_thread_cpu_mask_*() APIs which control per-CPU affinity masks in
	  SMP mode, allowing applications to pin threads to specific CPUs or
	  disallow threads from running on given CPUs.  Note that as currently
	  implemented, this involves an inherent O(N) scaling in the number of
	  idle-but-runnable threads, and thus works only with the DUMB
	  scheduler (as SCALABLE and MULTIQ would see no benefit).

	  Note that this setting does not technically depend on SMP and is
	  implemented without it for testing purposes, but for obvious reasons
	  makes sense as an application API only where there is more than one
	  CPU.  With one CPU, it's just a higher overhead version of
	  k_thread_start/stop().

config MAIN_STACK_SIZE
	int "Size of stack for initialization and main thread"
	default 2048 if COVERAGE_GCOV
	default 512 if ZTEST && !(RISCV || X86)
	default 1024
	help
	  When the initialization is complete, the thread executing it then
	  executes the main() routine, so as to reuse the stack used by the
	  initialization, which would be wasted RAM otherwise.

	  After initialization is complete, the thread runs main().

config IDLE_STACK_SIZE
	int "Size of stack for idle thread"
	default 2048 if COVERAGE_GCOV
	default 1024 if XTENSA
	default 512 if RISCV
	default 384 if DYNAMIC_OBJECTS
	default 320 if ARC || (ARM && CPU_HAS_FPU) || (X86 && MMU)
	default 256
	help
	  Depending on the work that the idle task must do, most likely due to
	  power management but possibly to other features like system event
	  logging (e.g. logging when the system goes to sleep), the idle thread
	  may need more stack space than the default value.

config ISR_STACK_SIZE
	int "ISR and initialization stack size (in bytes)"
	default 2048
	help
	  This option specifies the size of the stack used by interrupt
	  service routines (ISRs), and during kernel initialization.

config THREAD_STACK_INFO
	bool "Thread stack info"
	help
	  This option allows each thread to store the thread stack info into
	  the k_thread data structure.

config THREAD_CUSTOM_DATA
	bool "Thread custom data"
	help
	  This option allows each thread to store 32 bits of custom data,
	  which can be accessed using the k_thread_custom_data_xxx() APIs.

config THREAD_USERSPACE_LOCAL_DATA
	bool
	depends on USERSPACE
	default y if ERRNO && !ERRNO_IN_TLS

config ERRNO
	bool "Enable errno support"
	default y
	help
	  Enable per-thread errno in the kernel. Application and library code must
	  include errno.h provided by the C library (libc) to use the errno
	  symbol. The C library must access the per-thread errno via the
	  z_errno() symbol.

config ERRNO_IN_TLS
	bool "Store errno in thread local storage (TLS)"
	depends on ERRNO && THREAD_LOCAL_STORAGE
	default y
	help
	  Use thread local storage to store errno instead of storing it in
	  the kernel thread struct. This avoids a syscall if userspace is enabled.

choice SCHED_ALGORITHM
	prompt "Scheduler priority queue algorithm"
	default SCHED_DUMB
	help
	  The kernel can be built with with several choices for the
	  ready queue implementation, offering different choices between
	  code size, constant factor runtime overhead and performance
	  scaling when many threads are added.

config SCHED_DUMB
	bool "Simple linked-list ready queue"
	help
	  When selected, the scheduler ready queue will be implemented
	  as a simple unordered list, with very fast constant time
	  performance for single threads and very low code size.
	  Choose this on systems with constrained code size that will
	  never see more than a small number (3, maybe) of runnable
	  threads in the queue at any given time.  On most platforms
	  (that are not otherwise using the red/black tree) this
	  results in a savings of ~2k of code size.

config SCHED_SCALABLE
	bool "Red/black tree ready queue"
	help
	  When selected, the scheduler ready queue will be implemented
	  as a red/black tree.  This has rather slower constant-time
	  insertion and removal overhead, and on most platforms (that
	  are not otherwise using the rbtree somewhere) requires an
	  extra ~2kb of code.  But the resulting behavior will scale
	  cleanly and quickly into the many thousands of threads.  Use
	  this on platforms where you may have many threads (very
	  roughly: more than 20 or so) marked as runnable at a given
	  time.  Most applications don't want this.

config SCHED_MULTIQ
	bool "Traditional multi-queue ready queue"
	depends on !SCHED_DEADLINE
	help
	  When selected, the scheduler ready queue will be implemented
	  as the classic/textbook array of lists, one per priority
	  (max 32 priorities).  This corresponds to the scheduler
	  algorithm used in Zephyr versions prior to 1.12.  It incurs
	  only a tiny code size overhead vs. the "dumb" scheduler and
	  runs in O(1) time in almost all circumstances with very low
	  constant factor.  But it requires a fairly large RAM budget
	  to store those list heads, and the limited features make it
	  incompatible with features like deadline scheduling that
	  need to sort threads more finely, and SMP affinity which
	  need to traverse the list of threads.  Typical applications
	  with small numbers of runnable threads probably want the
	  DUMB scheduler.

endchoice # SCHED_ALGORITHM

choice WAITQ_ALGORITHM
	prompt "Wait queue priority algorithm"
	default WAITQ_DUMB
	help
	  The wait_q abstraction used in IPC primitives to pend
	  threads for later wakeup shares the same backend data
	  structure choices as the scheduler, and can use the same
	  options.

config WAITQ_SCALABLE
	bool "Use scalable wait_q implementation"
	help
	  When selected, the wait_q will be implemented with a
	  balanced tree.  Choose this if you expect to have many
	  threads waiting on individual primitives.  There is a ~2kb
	  code size increase over WAITQ_DUMB (which may be shared with
	  SCHED_SCALABLE) if the rbtree is not used elsewhere in the
	  application, and pend/unpend operations on "small" queues
	  will be somewhat slower (though this is not generally a
	  performance path).

config WAITQ_DUMB
	bool "Simple linked-list wait_q"
	help
	  When selected, the wait_q will be implemented with a
	  doubly-linked list.  Choose this if you expect to have only
	  a few threads blocked on any single IPC primitive.

endchoice # WAITQ_ALGORITHM

menu "Kernel Debugging and Metrics"

config INIT_STACKS
	bool "Initialize stack areas"
	help
	  This option instructs the kernel to initialize stack areas with a
	  known value (0xaa) before they are first used, so that the high
	  water mark can be easily determined. This applies to the stack areas
	  for threads, as well as to the interrupt stack.

config BOOT_BANNER
	bool "Boot banner"
	default y
	depends on CONSOLE_HAS_DRIVER
	select PRINTK
	select EARLY_CONSOLE
	help
	  This option outputs a banner to the console device during boot up.

config BOOT_DELAY
	int "Boot delay in milliseconds"
	default 0
	help
	  This option delays bootup for the specified amount of
	  milliseconds. This is used to allow serial ports to get ready
	  before starting to print information on them during boot, as
	  some systems might boot to fast for a receiving endpoint to
	  detect the new USB serial bus, enumerate it and get ready to
	  receive before it actually gets data. A similar effect can be
	  achieved by waiting for DCD on the serial port--however, not
	  all serial ports have DCD.

config THREAD_MONITOR
	bool "Thread monitoring [EXPERIMENTAL]"
	help
	  This option instructs the kernel to maintain a list of all threads
	  (excluding those that have not yet started or have already
	  terminated).

config THREAD_NAME
	bool "Thread name [EXPERIMENTAL]"
	help
	  This option allows to set a name for a thread.

config THREAD_MAX_NAME_LEN
	int "Max length of a thread name"
	default 32
	range 8 128
	depends on THREAD_NAME
	help
	  Thread names get stored in the k_thread struct. Indicate the max
	  name length, including the terminating NULL byte. Reduce this value
	  to conserve memory.

config INSTRUMENT_THREAD_SWITCHING
	bool

menuconfig THREAD_RUNTIME_STATS
	bool "Thread runtime statistics"
	select INSTRUMENT_THREAD_SWITCHING
	help
	  Gather thread runtime statistics.

	  For example:
	    - Thread total execution cycles

if THREAD_RUNTIME_STATS

config THREAD_RUNTIME_STATS_USE_TIMING_FUNCTIONS
	bool "Use timing functions to gather statistics"
	select TIMING_FUNCTIONS
	help
	  Use timing functions to gather thread runtime statistics.

	  Note that timing functions may use a different timer than
	  the default timer for OS timekeeping.

endif # THREAD_RUNTIME_STATS

endmenu

menu "Work Queue Options"
config SYSTEM_WORKQUEUE_STACK_SIZE
	int "System workqueue stack size"
	default 4096 if COVERAGE
	default 1024

config SYSTEM_WORKQUEUE_PRIORITY
	int "System workqueue priority"
	default -2 if COOP_ENABLED && !PREEMPT_ENABLED
	default  0 if !COOP_ENABLED
	default -1
	help
	  By default, system work queue priority is the lowest cooperative
	  priority. This means that any work handler, once started, won't
	  be preempted by any other thread until finished.

endmenu

menu "Atomic Operations"
config ATOMIC_OPERATIONS_BUILTIN
	bool
	help
	  Use the compiler builtin functions for atomic operations. This is
	  the preferred method. However, support for all arches in GCC is
	  incomplete.

config ATOMIC_OPERATIONS_CUSTOM
	bool
	help
	  Use when there isn't support for compiler built-ins, but you have
	  written optimized assembly code under arch/ which implements these.

config ATOMIC_OPERATIONS_C
	bool
	help
	  Use atomic operations routines that are implemented entirely
	  in C by locking interrupts. Selected by architectures which either
	  do not have support for atomic operations in their instruction
	  set, or haven't been implemented yet during bring-up, and also
	  the compiler does not have support for the atomic __sync_* builtins.
endmenu

menu "Timer API Options"

config TIMESLICING
	bool "Thread time slicing"
	default y
	depends on SYS_CLOCK_EXISTS && (NUM_PREEMPT_PRIORITIES != 0)
	help
	  This option enables time slicing between preemptible threads of
	  equal priority.

config TIMESLICE_SIZE
	int "Time slice size (in ms)"
	default 0
	range 0 2147483647
	depends on TIMESLICING
	help
	  This option specifies the maximum amount of time a thread can execute
	  before other threads of equal priority are given an opportunity to run.
	  A time slice size of zero means "no limit" (i.e. an infinitely large
	  time slice).

config TIMESLICE_PRIORITY
	int "Time slicing thread priority ceiling"
	default 0
	range 0 NUM_PREEMPT_PRIORITIES
	depends on TIMESLICING
	help
	  This option specifies the thread priority level at which time slicing
	  takes effect; threads having a higher priority than this ceiling are
	  not subject to time slicing.

config POLL
	bool "Async I/O Framework"
	help
	  Asynchronous notification framework. Enable the k_poll() and
	  k_poll_signal_raise() APIs.  The former can wait on multiple events
	  concurrently, which can be either directly triggered or triggered by
	  the availability of some kernel objects (semaphores and FIFOs).

endmenu

menu "Other Kernel Object Options"

config MEM_SLAB_TRACE_MAX_UTILIZATION
	bool "Enable getting maximum slab utilization"
	help
	  This adds variable to the k_mem_slab structure to hold
	  maximum utilization of the slab.

config NUM_MBOX_ASYNC_MSGS
	int "Maximum number of in-flight asynchronous mailbox messages"
	default 10
	help
	  This option specifies the total number of asynchronous mailbox
	  messages that can exist simultaneously, across all mailboxes
	  in the system.

	  Setting this option to 0 disables support for asynchronous
	  mailbox messages.

config NUM_PIPE_ASYNC_MSGS
	int "Maximum number of in-flight asynchronous pipe messages"
	default 10
	help
	  This option specifies the total number of asynchronous pipe
	  messages that can exist simultaneously, across all pipes in
	  the system.

	  Setting this option to 0 disables support for asynchronous
	  pipe messages.

config KERNEL_MEM_POOL
	bool "Use Kernel Memory Pool"
	default y
	help
	  Enable the use of kernel memory pool.

	  Say y if unsure.

if KERNEL_MEM_POOL

config HEAP_MEM_POOL_SIZE
	int "Heap memory pool size (in bytes)"
	default 0 if !POSIX_MQUEUE
	default 1024 if POSIX_MQUEUE
	help
	  This option specifies the size of the heap memory pool used when
	  dynamically allocating memory using k_malloc(). The maximum size of
	  the memory pool is only limited to available memory. A size of zero
	  means that no heap memory pool is defined.

endif # KERNEL_MEM_POOL

endmenu

config ARCH_HAS_CUSTOM_SWAP_TO_MAIN
	bool
	help
	  It's possible that an architecture port cannot use _Swap() to swap to
	  the _main() thread, but instead must do something custom. It must
	  enable this option in that case.

config SWAP_NONATOMIC
	bool
	help
	  On some architectures, the _Swap() primitive cannot be made
	  atomic with respect to the irq_lock being released.  That
	  is, interrupts may be received between the entry to _Swap
	  and the completion of the context switch.  There are a
	  handful of workaround cases in the kernel that need to be
	  enabled when this is true.  Currently, this only happens on
	  ARM when the PendSV exception priority sits below that of
	  Zephyr-handled interrupts.

config ARCH_HAS_CUSTOM_BUSY_WAIT
	bool
	help
	  It's possible that an architecture port cannot or does not want to use
	  the provided k_busy_wait(), but instead must do something custom. It must
	  enable this option in that case.

config SYS_CLOCK_TICKS_PER_SEC
	int "System tick frequency (in ticks/second)"
	default 100 if QEMU_TARGET || SOC_POSIX
	default 10000 if TICKLESS_CAPABLE
	default 100
	help
	  This option specifies the nominal frequency of the system clock in Hz.

	  For asynchronous timekeeping, the kernel defines a "ticks" concept. A
	  "tick" is the internal count in which the kernel does all its internal
	  uptime and timeout bookeeping. Interrupts are expected to be delivered
	  on tick boundaries to the extent practical, and no fractional ticks
	  are tracked.

	  The choice of tick rate is configurable by this option. Also the number
	  of cycles per tick should be chosen so that 1 millisecond is exactly
	  represented by an integral number of ticks. Defaults on most hardware
	  platforms (ones that support setting arbitrary interrupt timeouts) are
	  expected to be in the range of 10 kHz, with software emulation
	  platforms and legacy drivers using a more traditional 100 Hz value.

	  Note that when available and enabled, in "tickless" mode
	  this config variable specifies the minimum available timing
	  granularity, not necessarily the number or frequency of
	  interrupts delivered to the kernel.

	  A value of 0 completely disables timer support in the kernel.

config SYS_CLOCK_HW_CYCLES_PER_SEC
	int "System clock's h/w timer frequency"
	help
	  This option specifies the frequency of the hardware timer used for the
	  system clock (in Hz). This option is set by the SOC's or board's Kconfig file
	  and the user should generally avoid modifying it via the menu configuration.

config SYS_CLOCK_EXISTS
	bool "System clock exists and is enabled"
	default y
	help
	  This option specifies that the kernel lacks timer support.
	  Some device configurations can eliminate significant code if
	  this is disabled.  Obviously timeout-related APIs will not
	  work.

config TIMEOUT_64BIT
	bool "Store kernel timeouts in 64 bit precision"
	default y
	help
	  When this option is true, the k_ticks_t values passed to
	  kernel APIs will be a 64 bit quantity, allowing the use of
	  larger values (and higher precision tick rates) without fear
	  of overflowing the 32 bit word.  This feature also gates the
	  availability of absolute timeout values (which require the
	  extra precision).

config XIP
	bool "Execute in place"
	help
	  This option allows the kernel to operate with its text and read-only
	  sections residing in ROM (or similar read-only memory). Not all boards
	  support this option so it must be used with care; you must also
	  supply a linker command file when building your image. Enabling this
	  option increases both the code and data footprint of the image.

menu "Initialization Priorities"

config KERNEL_INIT_PRIORITY_OBJECTS
	int "Kernel objects initialization priority"
	default 30
	help
	  Kernel objects use this priority for initialization. This
	  priority needs to be higher than minimal default initialization
	  priority.

config KERNEL_INIT_PRIORITY_DEFAULT
	int "Default init priority"
	default 40
	help
	  Default minimal init priority for each init level.

config KERNEL_INIT_PRIORITY_DEVICE
	int "Default init priority for device drivers"
	default 50
	help
	  Device driver, that depends on common components, such as
	  interrupt controller, but does not depend on other devices,
	  uses this init priority.

config APPLICATION_INIT_PRIORITY
	int "Default init priority for application level drivers"
	default 90
	help
	  This priority level is for end-user drivers such as sensors and display
	  which have no inward dependencies.


endmenu

menu "Security Options"

config STACK_CANARIES
	bool "Compiler stack canaries"
	depends on ENTROPY_GENERATOR || TEST_RANDOM_GENERATOR
	help
	  This option enables compiler stack canaries.

	  If stack canaries are supported by the compiler, it will emit
	  extra code that inserts a canary value into the stack frame when
	  a function is entered and validates this value upon exit.
	  Stack corruption (such as that caused by buffer overflow) results
	  in a fatal error condition for the running entity.
	  Enabling this option can result in a significant increase
	  in footprint and an associated decrease in performance.

	  If stack canaries are not supported by the compiler an error
	  will occur at build time.

config EXECUTE_XOR_WRITE
	bool "Enable W^X for memory partitions"
	depends on USERSPACE
	depends on ARCH_HAS_EXECUTABLE_PAGE_BIT
	default y
	help
	  When enabled, will enforce that a writable page isn't executable
	  and vice versa.  This might not be acceptable in all scenarios,
	  so this option is given for those unafraid of shooting themselves
	  in the foot.

	  If unsure, say Y.

config STACK_POINTER_RANDOM
	int "Initial stack pointer randomization bounds"
	depends on !STACK_GROWS_UP
	depends on MULTITHREADING
	depends on TEST_RANDOM_GENERATOR || ENTROPY_HAS_DRIVER
	default 0
	help
	  This option performs a limited form of Address Space Layout
	  Randomization by offsetting some random value to a thread's
	  initial stack pointer upon creation. This hinders some types of
	  security attacks by making the location of any given stack frame
	  non-deterministic.

	  This feature can waste up to the specified size in bytes the stack
	  region, which is carved out of the total size of the stack region.
	  A reasonable minimum value would be around 100 bytes if this can
	  be spared.

	  This is currently only implemented for systems whose stack pointers
	  grow towards lower memory addresses.

config BOUNDS_CHECK_BYPASS_MITIGATION
	bool "Enable bounds check bypass mitigations for speculative execution"
	depends on USERSPACE
	help
	  Untrusted parameters from user mode may be used in system calls to
	  index arrays during speculative execution, also known as the Spectre
	  V1 vulnerability. When enabled, various macros defined in
	  misc/speculation.h will insert fence instructions or other appropriate
	  mitigations after bounds checking any array index parameters passed
	  in from untrusted sources (user mode threads). When disabled, these
	  macros do nothing.
endmenu

config MAX_DOMAIN_PARTITIONS
	int "Maximum number of partitions per memory domain"
	default 16
	range 0 255
	depends on USERSPACE
	help
	  Configure the maximum number of partitions per memory domain.

config ARCH_MEM_DOMAIN_DATA
	bool
	depends on USERSPACE
	help
	  This hidden option is selected by the target architecture if
	  architecture-specific data is needed on a per memory domain basis.
	  If so, the architecture defines a 'struct arch_mem_domain' which is
	  embedded within every struct k_mem_domain. The architecture
	  must also define the arch_mem_domain_init() function to set this up
	  when a memory domain is created.

	  Typical uses might be a set of page tables for that memory domain.

config ARCH_MEM_DOMAIN_SYNCHRONOUS_API
	bool
	depends on USERSPACE
	help
	  This hidden option is selected by the target architecture if
	  modifying a memory domain's partitions at runtime, or changing
	  a memory domain's thread membership requires synchronous calls
	  into the architecture layer.

	  If enabled, the architecture layer must implement the following
	  APIs:

	  arch_mem_domain_thread_add
	  arch_mem_domain_thread_remove
	  arch_mem_domain_partition_remove
	  arch_mem_domain_partition_add
	  arch_mem_domain_destroy

	  It's important to note that although supervisor threads can be
	  members of memory domains, they have no implications on supervisor
	  thread access to memory. Memory domain APIs may only be invoked from
	  supervisor mode.

	  For these reasons, on uniprocessor systems unless memory access
	  policy is managed in separate software constructions like page
	  tables, these APIs don't need to be implemented as the underlying
	  memory management hardware will be reprogrammed on context switch
	  anyway.

menu "SMP Options"

config USE_SWITCH
	bool "Use new-style _arch_switch instead of arch_swap"
	depends on USE_SWITCH_SUPPORTED
	help
	  The _arch_switch() API is a lower level context switching
	  primitive than the original arch_swap mechanism.  It is required
	  for an SMP-aware scheduler, or if the architecture does not
	  provide arch_swap.  In uniprocess situations where the
	  architecture provides both, _arch_switch incurs more somewhat
	  overhead and may be slower.

config USE_SWITCH_SUPPORTED
	bool
	help
	  Indicates whether _arch_switch() API is supported by the
	  currently enabled platform. This option should be selected by
	  platforms that implement it.

config SMP
	bool "Enable symmetric multithreading support"
	depends on USE_SWITCH
	help
	  When true, kernel will be built with SMP support, allowing
	  more than one CPU to schedule Zephyr tasks at a time.

config MP_NUM_CPUS
	int "Number of CPUs/cores"
	default 1
	range 1 4
	help
	  Number of multiprocessing-capable cores available to the
	  multicpu API and SMP features.

config SCHED_IPI_SUPPORTED
	bool
	help
	  True if the architecture supports a call to
	  arch_sched_ipi() to broadcast an interrupt that will call
	  z_sched_ipi() on other CPUs in the system.  Required for
	  k_thread_abort() to operate with reasonable latency
	  (otherwise we might have to wait for the other thread to
	  take an interrupt, which can be arbitrarily far in the
	  future).

config TRACE_SCHED_IPI
	bool "Enable Test IPI"
	help
	  When true, it will add a hook into z_sched_ipi(), in order
	  to check if schedule IPI has called or not, for testing
	  purpose.
	depends on SCHED_IPI_SUPPORTED
	depends on MP_NUM_CPUS>1

config KERNEL_COHERENCE
	bool "Place all shared data into coherent memory"
	depends on ARCH_HAS_COHERENCE
	default y if SMP && MP_NUM_CPUS > 1
	select THREAD_STACK_INFO
	help
	  When available and selected, the kernel will build in a mode
	  where all shared data is placed in multiprocessor-coherent
	  (generally "uncached") memory.  Thread stacks will remain
	  cached, as will application memory declared with
	  __incoherent.  This is intended for Zephyr SMP kernels
	  running on cache-incoherent architectures only.  Note that
	  when this is selected, there is an implicit API change that
	  assumes cache coherence to any memory passed to the kernel.
	  Code that creates kernel data structures in uncached regions
	  may fail strangely.  Some assertions exist to catch these
	  mistakes, but not all circumstances can be tested.

endmenu

config TICKLESS_IDLE
	# NB: This option is deprecated, see TICKLESS_KERNEL and
	# https://github.com/zephyrproject-rtos/zephyr/pull/12234
	bool "Tickless idle"
	default y if PM || TICKLESS_CAPABLE
	help
	  This option suppresses periodic system clock interrupts whenever the
	  kernel becomes idle. This permits the system to remain in a power
	  saving state for extended periods without having to wake up to
	  service each tick as it occurs.

config TICKLESS_IDLE_THRESH
	int "Tickless idle threshold"
	default 3
	depends on TICKLESS_IDLE
	help
	  This option enables clock interrupt suppression when the kernel idles
	  for only a short period of time. It specifies the minimum number of
	  ticks that must occur before the next kernel timer expires in order
	  for suppression to happen.

config TICKLESS_KERNEL
	bool "Tickless kernel"
	default y if TICKLESS_CAPABLE
	depends on TICKLESS_CAPABLE
	help
	  This option enables a fully event driven kernel. Periodic system
	  clock interrupt generation would be stopped at all times.

config TOOLCHAIN_SUPPORTS_THREAD_LOCAL_STORAGE
	bool
	default y if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr"
	help
	  Hidden option to signal that toolchain supports generating code
	  with thread local storage.

config THREAD_LOCAL_STORAGE
	bool "Thread Local Storage (TLS)"
	depends on ARCH_HAS_THREAD_LOCAL_STORAGE && TOOLCHAIN_SUPPORTS_THREAD_LOCAL_STORAGE
	select NEED_LIBC_MEM_PARTITION if (CPU_CORTEX_M && USERSPACE)
	help
	  This option enables thread local storage (TLS) support in kernel.

endmenu