soundwire: cadence: further simplify low-level xfer_msg_defer() callback
[linux-block.git] / kernel / Kconfig.preempt
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ec8f24b7 1# SPDX-License-Identifier: GPL-2.0-only
cc19ca86 2
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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
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14choice
15 prompt "Preemption Model"
a8b76910 16 default PREEMPT_NONE
f8cbd99b 17
a8b76910 18config PREEMPT_NONE
f8cbd99b 19 bool "No Forced Preemption (Server)"
a8b76910 20 select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
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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
a8b76910 32config PREEMPT_VOLUNTARY
f8cbd99b 33 bool "Voluntary Kernel Preemption (Desktop)"
87a4c375 34 depends on !ARCH_NO_PREEMPT
a8b76910 35 select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
cc19ca86 36 help
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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,
3dde6ad8 41 at the cost of slightly lower throughput.
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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
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47 under load.
48
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49 Select this if you are building a kernel for a desktop system.
50
a8b76910 51config PREEMPT
f8cbd99b 52 bool "Preemptible Kernel (Low-Latency Desktop)"
87a4c375 53 depends on !ARCH_NO_PREEMPT
a8b76910 54 select PREEMPT_BUILD
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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
3dde6ad8 63 system is under load, at the cost of slightly lower throughput
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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
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70config PREEMPT_RT
71 bool "Fully Preemptible Kernel (Real-Time)"
a8b76910 72 depends on EXPERT && ARCH_SUPPORTS_RT
b8d33498 73 select PREEMPTION
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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
d61ca3c2 80 low level and critical code paths (entry code, scheduler, low
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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
f8cbd99b 87endchoice
cc19ca86 88
bdd4e85d 89config PREEMPT_COUNT
72367933 90 bool
a50a3f4b 91
b8d33498 92config PREEMPTION
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93 bool
94 select PREEMPT_COUNT
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95
96config PREEMPT_DYNAMIC
c597bfdd 97 bool "Preemption behaviour defined on boot"
a8b76910 98 depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
99cf983c 99 select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
a8b76910 100 select PREEMPT_BUILD
99cf983c 101 default y if HAVE_PREEMPT_DYNAMIC_CALL
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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.
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117
118config SCHED_CORE
119 bool "Core Scheduling for SMT"
9edeaea1 120 depends on SCHED_SMT
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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
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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.
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7dd5ad2d 136