[linux-2.6-block.git] / kernel / Kconfig.preempt

# SPDX-License-Identifier: GPL-2.0-only

config PREEMPT_NONE_BUILD
	bool

config PREEMPT_VOLUNTARY_BUILD
	bool

config PREEMPT_BUILD
	bool
	select PREEMPTION
	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK

choice
	prompt "Preemption Model"
	default PREEMPT_NONE

config PREEMPT_NONE
	bool "No Forced Preemption (Server)"
	select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
	help
	  This is the traditional Linux preemption model, geared towards
	  throughput. It will still provide good latencies most of the
	  time, but there are no guarantees and occasional longer delays
	  are possible.

	  Select this option if you are building a kernel for a server or
	  scientific/computation system, or if you want to maximize the
	  raw processing power of the kernel, irrespective of scheduling
	  latencies.

config PREEMPT_VOLUNTARY
	bool "Voluntary Kernel Preemption (Desktop)"
	depends on !ARCH_NO_PREEMPT
	select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
	help
	  This option reduces the latency of the kernel by adding more
	  "explicit preemption points" to the kernel code. These new
	  preemption points have been selected to reduce the maximum
	  latency of rescheduling, providing faster application reactions,
	  at the cost of slightly lower throughput.

	  This allows reaction to interactive events by allowing a
	  low priority process to voluntarily preempt itself even if it
	  is in kernel mode executing a system call. This allows
	  applications to run more 'smoothly' even when the system is
	  under load.

	  Select this if you are building a kernel for a desktop system.

config PREEMPT
	bool "Preemptible Kernel (Low-Latency Desktop)"
	depends on !ARCH_NO_PREEMPT
	select PREEMPT_BUILD
	help
	  This option reduces the latency of the kernel by making
	  all kernel code (that is not executing in a critical section)
	  preemptible.  This allows reaction to interactive events by
	  permitting a low priority process to be preempted involuntarily
	  even if it is in kernel mode executing a system call and would
	  otherwise not be about to reach a natural preemption point.
	  This allows applications to run more 'smoothly' even when the
	  system is under load, at the cost of slightly lower throughput
	  and a slight runtime overhead to kernel code.

	  Select this if you are building a kernel for a desktop or
	  embedded system with latency requirements in the milliseconds
	  range.

config PREEMPT_RT
	bool "Fully Preemptible Kernel (Real-Time)"
	depends on EXPERT && ARCH_SUPPORTS_RT
	select PREEMPTION
	help
	  This option turns the kernel into a real-time kernel by replacing
	  various locking primitives (spinlocks, rwlocks, etc.) with
	  preemptible priority-inheritance aware variants, enforcing
	  interrupt threading and introducing mechanisms to break up long
	  non-preemptible sections. This makes the kernel, except for very
	  low level and critical code paths (entry code, scheduler, low
	  level interrupt handling) fully preemptible and brings most
	  execution contexts under scheduler control.

	  Select this if you are building a kernel for systems which
	  require real-time guarantees.

endchoice

config PREEMPT_COUNT
       bool

config PREEMPTION
       bool
       select PREEMPT_COUNT

config PREEMPT_DYNAMIC
	bool "Preemption behaviour defined on boot"
	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
	select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
	select PREEMPT_BUILD
	default y if HAVE_PREEMPT_DYNAMIC_CALL
	help
	  This option allows to define the preemption model on the kernel
	  command line parameter and thus override the default preemption
	  model defined during compile time.

	  The feature is primarily interesting for Linux distributions which
	  provide a pre-built kernel binary to reduce the number of kernel
	  flavors they offer while still offering different usecases.

	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
	  but if runtime patching is not available for the specific architecture
	  then the potential overhead should be considered.

	  Interesting if you want the same pre-built kernel should be used for
	  both Server and Desktop workloads.

config SCHED_CORE
	bool "Core Scheduling for SMT"
	depends on SCHED_SMT
	help
	  This option permits Core Scheduling, a means of coordinated task
	  selection across SMT siblings. When enabled -- see
	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
	  will execute a task from the same 'core group', forcing idle when no
	  matching task is found.

	  Use of this feature includes:
	   - mitigation of some (not all) SMT side channels;
	   - limiting SMT interference to improve determinism and/or performance.

	  SCHED_CORE is default disabled. When it is enabled and unused,
	  which is the likely usage by Linux distributions, there should
	  be no measurable impact on performance.

config SCHED_CLASS_EXT
	bool "Extensible Scheduling Class"
	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
	select STACKTRACE if STACKTRACE_SUPPORT
	help
	  This option enables a new scheduler class sched_ext (SCX), which
	  allows scheduling policies to be implemented as BPF programs to
	  achieve the following:

	  - Ease of experimentation and exploration: Enabling rapid
	    iteration of new scheduling policies.
	  - Customization: Building application-specific schedulers which
	    implement policies that are not applicable to general-purpose
	    schedulers.
	  - Rapid scheduler deployments: Non-disruptive swap outs of
	    scheduling policies in production environments.

	  sched_ext leverages BPF struct_ops feature to define a structure
	  which exports function callbacks and flags to BPF programs that
	  wish to implement scheduling policies. The struct_ops structure
	  exported by sched_ext is struct sched_ext_ops, and is conceptually
	  similar to struct sched_class.

	  For more information:
	    Documentation/scheduler/sched-ext.rst
	    https://github.com/sched-ext/scx
Commit	Line	Data
	1	# SPDX-License-Identifier: GPL-2.0-only
	2
	3	config PREEMPT_NONE_BUILD
	4	bool
	5
	6	config PREEMPT_VOLUNTARY_BUILD
	7	bool
	8
	9	config PREEMPT_BUILD
	10	bool
	11	select PREEMPTION
	12	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
	13
	14	choice
	15	prompt "Preemption Model"
	16	default PREEMPT_NONE
	17
	18	config PREEMPT_NONE
	19	bool "No Forced Preemption (Server)"
	20	select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
	21	help
	22	This is the traditional Linux preemption model, geared towards
	23	throughput. It will still provide good latencies most of the
	24	time, but there are no guarantees and occasional longer delays
	25	are possible.
	26
	27	Select this option if you are building a kernel for a server or
	28	scientific/computation system, or if you want to maximize the
	29	raw processing power of the kernel, irrespective of scheduling
	30	latencies.
	31
	32	config PREEMPT_VOLUNTARY
	33	bool "Voluntary Kernel Preemption (Desktop)"
	34	depends on !ARCH_NO_PREEMPT
	35	select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
	36	help
	37	This option reduces the latency of the kernel by adding more
	38	"explicit preemption points" to the kernel code. These new
	39	preemption points have been selected to reduce the maximum
	40	latency of rescheduling, providing faster application reactions,
	41	at the cost of slightly lower throughput.
	42
	43	This allows reaction to interactive events by allowing a
	44	low priority process to voluntarily preempt itself even if it
	45	is in kernel mode executing a system call. This allows
	46	applications to run more 'smoothly' even when the system is
	47	under load.
	48
	49	Select this if you are building a kernel for a desktop system.
	50
	51	config PREEMPT
	52	bool "Preemptible Kernel (Low-Latency Desktop)"
	53	depends on !ARCH_NO_PREEMPT
	54	select PREEMPT_BUILD
	55	help
	56	This option reduces the latency of the kernel by making
	57	all kernel code (that is not executing in a critical section)
	58	preemptible. This allows reaction to interactive events by
	59	permitting a low priority process to be preempted involuntarily
	60	even if it is in kernel mode executing a system call and would
	61	otherwise not be about to reach a natural preemption point.
	62	This allows applications to run more 'smoothly' even when the
	63	system is under load, at the cost of slightly lower throughput
	64	and a slight runtime overhead to kernel code.
	65
	66	Select this if you are building a kernel for a desktop or
	67	embedded system with latency requirements in the milliseconds
	68	range.
	69
	70	config PREEMPT_RT
	71	bool "Fully Preemptible Kernel (Real-Time)"
	72	depends on EXPERT && ARCH_SUPPORTS_RT
	73	select PREEMPTION
	74	help
	75	This option turns the kernel into a real-time kernel by replacing
	76	various locking primitives (spinlocks, rwlocks, etc.) with
	77	preemptible priority-inheritance aware variants, enforcing
	78	interrupt threading and introducing mechanisms to break up long
	79	non-preemptible sections. This makes the kernel, except for very
	80	low level and critical code paths (entry code, scheduler, low
	81	level interrupt handling) fully preemptible and brings most
	82	execution contexts under scheduler control.
	83
	84	Select this if you are building a kernel for systems which
	85	require real-time guarantees.
	86
	87	endchoice
	88
	89	config PREEMPT_COUNT
	90	bool
	91
	92	config PREEMPTION
	93	bool
	94	select PREEMPT_COUNT
	95
	96	config PREEMPT_DYNAMIC
	97	bool "Preemption behaviour defined on boot"
	98	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
	99	select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
	100	select PREEMPT_BUILD
	101	default y if HAVE_PREEMPT_DYNAMIC_CALL
	102	help
	103	This option allows to define the preemption model on the kernel
	104	command line parameter and thus override the default preemption
	105	model defined during compile time.
	106
	107	The feature is primarily interesting for Linux distributions which
	108	provide a pre-built kernel binary to reduce the number of kernel
	109	flavors they offer while still offering different usecases.
	110
	111	The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
	112	but if runtime patching is not available for the specific architecture
	113	then the potential overhead should be considered.
	114
	115	Interesting if you want the same pre-built kernel should be used for
	116	both Server and Desktop workloads.
	117
	118	config SCHED_CORE
	119	bool "Core Scheduling for SMT"
	120	depends on SCHED_SMT
	121	help
	122	This option permits Core Scheduling, a means of coordinated task
	123	selection across SMT siblings. When enabled -- see
	124	prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
	125	will execute a task from the same 'core group', forcing idle when no
	126	matching task is found.
	127
	128	Use of this feature includes:
	129	- mitigation of some (not all) SMT side channels;
	130	- limiting SMT interference to improve determinism and/or performance.
	131
	132	SCHED_CORE is default disabled. When it is enabled and unused,
	133	which is the likely usage by Linux distributions, there should
	134	be no measurable impact on performance.
	135
	136	config SCHED_CLASS_EXT
	137	bool "Extensible Scheduling Class"
	138	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
	139	select STACKTRACE if STACKTRACE_SUPPORT
	140	help
	141	This option enables a new scheduler class sched_ext (SCX), which
	142	allows scheduling policies to be implemented as BPF programs to
	143	achieve the following:
	144
	145	- Ease of experimentation and exploration: Enabling rapid
	146	iteration of new scheduling policies.
	147	- Customization: Building application-specific schedulers which
	148	implement policies that are not applicable to general-purpose
	149	schedulers.
	150	- Rapid scheduler deployments: Non-disruptive swap outs of
	151	scheduling policies in production environments.
	152
	153	sched_ext leverages BPF struct_ops feature to define a structure
	154	which exports function callbacks and flags to BPF programs that
	155	wish to implement scheduling policies. The struct_ops structure
	156	exported by sched_ext is struct sched_ext_ops, and is conceptually
	157	similar to struct sched_class.
	158
	159	For more information:
	160	Documentation/scheduler/sched-ext.rst
	161	https://github.com/sched-ext/scx