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ec8f24b7 | 1 | # SPDX-License-Identifier: GPL-2.0-only |
cc19ca86 | 2 | |
f8cbd99b IM |
3 | choice |
4 | prompt "Preemption Model" | |
c597bfdd | 5 | default PREEMPT_NONE_BEHAVIOUR |
f8cbd99b | 6 | |
c597bfdd | 7 | config PREEMPT_NONE_BEHAVIOUR |
f8cbd99b | 8 | bool "No Forced Preemption (Server)" |
c597bfdd | 9 | select PREEMPT_NONE if !PREEMPT_DYNAMIC |
f8cbd99b IM |
10 | help |
11 | This is the traditional Linux preemption model, geared towards | |
12 | throughput. It will still provide good latencies most of the | |
13 | time, but there are no guarantees and occasional longer delays | |
14 | are possible. | |
15 | ||
16 | Select this option if you are building a kernel for a server or | |
17 | scientific/computation system, or if you want to maximize the | |
18 | raw processing power of the kernel, irrespective of scheduling | |
19 | latencies. | |
20 | ||
c597bfdd | 21 | config PREEMPT_VOLUNTARY_BEHAVIOUR |
f8cbd99b | 22 | bool "Voluntary Kernel Preemption (Desktop)" |
87a4c375 | 23 | depends on !ARCH_NO_PREEMPT |
c597bfdd | 24 | select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC |
cc19ca86 | 25 | help |
f8cbd99b IM |
26 | This option reduces the latency of the kernel by adding more |
27 | "explicit preemption points" to the kernel code. These new | |
28 | preemption points have been selected to reduce the maximum | |
29 | latency of rescheduling, providing faster application reactions, | |
3dde6ad8 | 30 | at the cost of slightly lower throughput. |
f8cbd99b IM |
31 | |
32 | This allows reaction to interactive events by allowing a | |
33 | low priority process to voluntarily preempt itself even if it | |
34 | is in kernel mode executing a system call. This allows | |
35 | applications to run more 'smoothly' even when the system is | |
cc19ca86 IM |
36 | under load. |
37 | ||
f8cbd99b IM |
38 | Select this if you are building a kernel for a desktop system. |
39 | ||
c597bfdd | 40 | config PREEMPT_BEHAVIOUR |
f8cbd99b | 41 | bool "Preemptible Kernel (Low-Latency Desktop)" |
87a4c375 | 42 | depends on !ARCH_NO_PREEMPT |
c597bfdd | 43 | select PREEMPT |
f8cbd99b IM |
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 | |
3dde6ad8 | 52 | system is under load, at the cost of slightly lower throughput |
f8cbd99b IM |
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 | ||
a50a3f4b TG |
59 | config PREEMPT_RT |
60 | bool "Fully Preemptible Kernel (Real-Time)" | |
c597bfdd | 61 | depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC |
b8d33498 | 62 | select PREEMPTION |
a50a3f4b TG |
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 | |
d61ca3c2 | 69 | low level and critical code paths (entry code, scheduler, low |
a50a3f4b TG |
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 | ||
f8cbd99b | 76 | endchoice |
cc19ca86 | 77 | |
c597bfdd FW |
78 | config PREEMPT_NONE |
79 | bool | |
80 | ||
81 | config PREEMPT_VOLUNTARY | |
82 | bool | |
83 | ||
84 | config PREEMPT | |
85 | bool | |
86 | select PREEMPTION | |
87 | select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK | |
88 | ||
bdd4e85d | 89 | config PREEMPT_COUNT |
72367933 | 90 | bool |
a50a3f4b | 91 | |
b8d33498 | 92 | config PREEMPTION |
a50a3f4b TG |
93 | bool |
94 | select PREEMPT_COUNT | |
6ef869e0 MH |
95 | |
96 | config PREEMPT_DYNAMIC | |
c597bfdd FW |
97 | bool "Preemption behaviour defined on boot" |
98 | depends on HAVE_PREEMPT_DYNAMIC | |
99 | select PREEMPT | |
100 | default y | |
6ef869e0 MH |
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. | |
9edeaea1 PZ |
116 | |
117 | config SCHED_CORE | |
118 | bool "Core Scheduling for SMT" | |
9edeaea1 | 119 | depends on SCHED_SMT |
7b419f47 PZ |
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 | ||
d2343cb8 IM |
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. | |
7b419f47 | 134 | |
9edeaea1 | 135 |