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1
2choice
3 prompt "Preemption Model"
4 default PREEMPT_NONE
5
6config PREEMPT_NONE
7 bool "No Forced Preemption (Server)"
8 help
9 This is the traditional Linux preemption model, geared towards
10 throughput. It will still provide good latencies most of the
11 time, but there are no guarantees and occasional longer delays
12 are possible.
13
14 Select this option if you are building a kernel for a server or
15 scientific/computation system, or if you want to maximize the
16 raw processing power of the kernel, irrespective of scheduling
17 latencies.
18
19config PREEMPT_VOLUNTARY
20 bool "Voluntary Kernel Preemption (Desktop)"
21 help
22 This option reduces the latency of the kernel by adding more
23 "explicit preemption points" to the kernel code. These new
24 preemption points have been selected to reduce the maximum
25 latency of rescheduling, providing faster application reactions,
26 at the cost of slightly lower throughput.
27
28 This allows reaction to interactive events by allowing a
29 low priority process to voluntarily preempt itself even if it
30 is in kernel mode executing a system call. This allows
31 applications to run more 'smoothly' even when the system is
32 under load.
33
34 Select this if you are building a kernel for a desktop system.
35
36config PREEMPT
37 bool "Preemptible Kernel (Low-Latency Desktop)"
38 select PREEMPT_COUNT
39 select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
40 help
41 This option reduces the latency of the kernel by making
42 all kernel code (that is not executing in a critical section)
43 preemptible. This allows reaction to interactive events by
44 permitting a low priority process to be preempted involuntarily
45 even if it is in kernel mode executing a system call and would
46 otherwise not be about to reach a natural preemption point.
47 This allows applications to run more 'smoothly' even when the
48 system is under load, at the cost of slightly lower throughput
49 and a slight runtime overhead to kernel code.
50
51 Select this if you are building a kernel for a desktop or
52 embedded system with latency requirements in the milliseconds
53 range.
54
55endchoice
56
57config PREEMPT_COUNT
58
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 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
118config 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