1# SPDX-License-Identifier: GPL-2.0-only
2
3config PREEMPT_NONE_BUILD
4	bool
5
6config PREEMPT_VOLUNTARY_BUILD
7	bool
8
9config PREEMPT_BUILD
10	bool
11	select PREEMPTION
12	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
13
14choice
15	prompt "Preemption Model"
16	default PREEMPT_NONE
17
18config 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
32config 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
51config 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
70config 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
87endchoice
88
89config PREEMPT_COUNT
90       bool
91
92config PREEMPTION
93       bool
94       select PREEMPT_COUNT
95
96config PREEMPT_DYNAMIC
97	bool "Preemption behaviour defined on boot"
98	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
99	select PREEMPT_BUILD
100	default y
101	help
102	  This option allows to define the preemption model on the kernel
103	  command line parameter and thus override the default preemption
104	  model defined during compile time.
105
106	  The feature is primarily interesting for Linux distributions which
107	  provide a pre-built kernel binary to reduce the number of kernel
108	  flavors they offer while still offering different usecases.
109
110	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
111	  but if runtime patching is not available for the specific architecture
112	  then the potential overhead should be considered.
113
114	  Interesting if you want the same pre-built kernel should be used for
115	  both Server and Desktop workloads.
116
117config SCHED_CORE
118	bool "Core Scheduling for SMT"
119	depends on SCHED_SMT
120	help
121	  This option permits Core Scheduling, a means of coordinated task
122	  selection across SMT siblings. When enabled -- see
123	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
124	  will execute a task from the same 'core group', forcing idle when no
125	  matching task is found.
126
127	  Use of this feature includes:
128	   - mitigation of some (not all) SMT side channels;
129	   - limiting SMT interference to improve determinism and/or performance.
130
131	  SCHED_CORE is default disabled. When it is enabled and unused,
132	  which is the likely usage by Linux distributions, there should
133	  be no measurable impact on performance.
134
135
136