1# SPDX-License-Identifier: GPL-2.0-only
2
3choice
4	prompt "Preemption Model"
5	default PREEMPT_NONE
6
7config PREEMPT_NONE
8	bool "No Forced Preemption (Server)"
9	help
10	  This is the traditional Linux preemption model, geared towards
11	  throughput. It will still provide good latencies most of the
12	  time, but there are no guarantees and occasional longer delays
13	  are possible.
14
15	  Select this option if you are building a kernel for a server or
16	  scientific/computation system, or if you want to maximize the
17	  raw processing power of the kernel, irrespective of scheduling
18	  latencies.
19
20config PREEMPT_VOLUNTARY
21	bool "Voluntary Kernel Preemption (Desktop)"
22	depends on !ARCH_NO_PREEMPT
23	help
24	  This option reduces the latency of the kernel by adding more
25	  "explicit preemption points" to the kernel code. These new
26	  preemption points have been selected to reduce the maximum
27	  latency of rescheduling, providing faster application reactions,
28	  at the cost of slightly lower throughput.
29
30	  This allows reaction to interactive events by allowing a
31	  low priority process to voluntarily preempt itself even if it
32	  is in kernel mode executing a system call. This allows
33	  applications to run more 'smoothly' even when the system is
34	  under load.
35
36	  Select this if you are building a kernel for a desktop system.
37
38config PREEMPT
39	bool "Preemptible Kernel (Low-Latency Desktop)"
40	depends on !ARCH_NO_PREEMPT
41	select PREEMPTION
42	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
43	select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC
44	help
45	  This option reduces the latency of the kernel by making
46	  all kernel code (that is not executing in a critical section)
47	  preemptible.  This allows reaction to interactive events by
48	  permitting a low priority process to be preempted involuntarily
49	  even if it is in kernel mode executing a system call and would
50	  otherwise not be about to reach a natural preemption point.
51	  This allows applications to run more 'smoothly' even when the
52	  system is under load, at the cost of slightly lower throughput
53	  and a slight runtime overhead to kernel code.
54
55	  Select this if you are building a kernel for a desktop or
56	  embedded system with latency requirements in the milliseconds
57	  range.
58
59config PREEMPT_RT
60	bool "Fully Preemptible Kernel (Real-Time)"
61	depends on EXPERT && ARCH_SUPPORTS_RT
62	select PREEMPTION
63	help
64	  This option turns the kernel into a real-time kernel by replacing
65	  various locking primitives (spinlocks, rwlocks, etc.) with
66	  preemptible priority-inheritance aware variants, enforcing
67	  interrupt threading and introducing mechanisms to break up long
68	  non-preemptible sections. This makes the kernel, except for very
69	  low level and critical code paths (entry code, scheduler, low
70	  level interrupt handling) fully preemptible and brings most
71	  execution contexts under scheduler control.
72
73	  Select this if you are building a kernel for systems which
74	  require real-time guarantees.
75
76endchoice
77
78config PREEMPT_COUNT
79       bool
80
81config PREEMPTION
82       bool
83       select PREEMPT_COUNT
84
85config PREEMPT_DYNAMIC
86	bool
87	help
88	  This option allows to define the preemption model on the kernel
89	  command line parameter and thus override the default preemption
90	  model defined during compile time.
91
92	  The feature is primarily interesting for Linux distributions which
93	  provide a pre-built kernel binary to reduce the number of kernel
94	  flavors they offer while still offering different usecases.
95
96	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
97	  but if runtime patching is not available for the specific architecture
98	  then the potential overhead should be considered.
99
100	  Interesting if you want the same pre-built kernel should be used for
101	  both Server and Desktop workloads.
102
103config SCHED_CORE
104	bool "Core Scheduling for SMT"
105	depends on SCHED_SMT
106	help
107	  This option permits Core Scheduling, a means of coordinated task
108	  selection across SMT siblings. When enabled -- see
109	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
110	  will execute a task from the same 'core group', forcing idle when no
111	  matching task is found.
112
113	  Use of this feature includes:
114	   - mitigation of some (not all) SMT side channels;
115	   - limiting SMT interference to improve determinism and/or performance.
116
117	  SCHED_CORE is default disabled. When it is enabled and unused,
118	  which is the likely usage by Linux distributions, there should
119	  be no measurable impact on performance.
120
121
122