xref: /openbmc/linux/kernel/Kconfig.preempt (revision 9edeaea1bc452372718837ed2ba775811baf1ba1)
1ec8f24b7SThomas Gleixner# SPDX-License-Identifier: GPL-2.0-only
2cc19ca86SIngo Molnar
3f8cbd99bSIngo Molnarchoice
4f8cbd99bSIngo Molnar	prompt "Preemption Model"
5f8cbd99bSIngo Molnar	default PREEMPT_NONE
6f8cbd99bSIngo Molnar
7f8cbd99bSIngo Molnarconfig PREEMPT_NONE
8f8cbd99bSIngo Molnar	bool "No Forced Preemption (Server)"
9cc19ca86SIngo Molnar	help
10f8cbd99bSIngo Molnar	  This is the traditional Linux preemption model, geared towards
11f8cbd99bSIngo Molnar	  throughput. It will still provide good latencies most of the
12f8cbd99bSIngo Molnar	  time, but there are no guarantees and occasional longer delays
13f8cbd99bSIngo Molnar	  are possible.
14f8cbd99bSIngo Molnar
15f8cbd99bSIngo Molnar	  Select this option if you are building a kernel for a server or
16f8cbd99bSIngo Molnar	  scientific/computation system, or if you want to maximize the
17f8cbd99bSIngo Molnar	  raw processing power of the kernel, irrespective of scheduling
18f8cbd99bSIngo Molnar	  latencies.
19f8cbd99bSIngo Molnar
20f8cbd99bSIngo Molnarconfig PREEMPT_VOLUNTARY
21f8cbd99bSIngo Molnar	bool "Voluntary Kernel Preemption (Desktop)"
2287a4c375SChristoph Hellwig	depends on !ARCH_NO_PREEMPT
23f8cbd99bSIngo Molnar	help
24f8cbd99bSIngo Molnar	  This option reduces the latency of the kernel by adding more
25f8cbd99bSIngo Molnar	  "explicit preemption points" to the kernel code. These new
26f8cbd99bSIngo Molnar	  preemption points have been selected to reduce the maximum
27f8cbd99bSIngo Molnar	  latency of rescheduling, providing faster application reactions,
283dde6ad8SDavid Sterba	  at the cost of slightly lower throughput.
29f8cbd99bSIngo Molnar
30f8cbd99bSIngo Molnar	  This allows reaction to interactive events by allowing a
31f8cbd99bSIngo Molnar	  low priority process to voluntarily preempt itself even if it
32f8cbd99bSIngo Molnar	  is in kernel mode executing a system call. This allows
33f8cbd99bSIngo Molnar	  applications to run more 'smoothly' even when the system is
34cc19ca86SIngo Molnar	  under load.
35cc19ca86SIngo Molnar
36f8cbd99bSIngo Molnar	  Select this if you are building a kernel for a desktop system.
37f8cbd99bSIngo Molnar
38b8d33498SThomas Gleixnerconfig PREEMPT
39f8cbd99bSIngo Molnar	bool "Preemptible Kernel (Low-Latency Desktop)"
4087a4c375SChristoph Hellwig	depends on !ARCH_NO_PREEMPT
41b8d33498SThomas Gleixner	select PREEMPTION
42e335e3ebSRaghavendra K T	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
436ef869e0SMichal Hocko	select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC
44f8cbd99bSIngo Molnar	help
45f8cbd99bSIngo Molnar	  This option reduces the latency of the kernel by making
46f8cbd99bSIngo Molnar	  all kernel code (that is not executing in a critical section)
47f8cbd99bSIngo Molnar	  preemptible.  This allows reaction to interactive events by
48f8cbd99bSIngo Molnar	  permitting a low priority process to be preempted involuntarily
49f8cbd99bSIngo Molnar	  even if it is in kernel mode executing a system call and would
50f8cbd99bSIngo Molnar	  otherwise not be about to reach a natural preemption point.
51f8cbd99bSIngo Molnar	  This allows applications to run more 'smoothly' even when the
523dde6ad8SDavid Sterba	  system is under load, at the cost of slightly lower throughput
53f8cbd99bSIngo Molnar	  and a slight runtime overhead to kernel code.
54f8cbd99bSIngo Molnar
55f8cbd99bSIngo Molnar	  Select this if you are building a kernel for a desktop or
56f8cbd99bSIngo Molnar	  embedded system with latency requirements in the milliseconds
57f8cbd99bSIngo Molnar	  range.
58f8cbd99bSIngo Molnar
59a50a3f4bSThomas Gleixnerconfig PREEMPT_RT
60a50a3f4bSThomas Gleixner	bool "Fully Preemptible Kernel (Real-Time)"
61a50a3f4bSThomas Gleixner	depends on EXPERT && ARCH_SUPPORTS_RT
62b8d33498SThomas Gleixner	select PREEMPTION
63a50a3f4bSThomas Gleixner	help
64a50a3f4bSThomas Gleixner	  This option turns the kernel into a real-time kernel by replacing
65a50a3f4bSThomas Gleixner	  various locking primitives (spinlocks, rwlocks, etc.) with
66a50a3f4bSThomas Gleixner	  preemptible priority-inheritance aware variants, enforcing
67a50a3f4bSThomas Gleixner	  interrupt threading and introducing mechanisms to break up long
68a50a3f4bSThomas Gleixner	  non-preemptible sections. This makes the kernel, except for very
69d61ca3c2SSrivatsa S. Bhat (VMware)	  low level and critical code paths (entry code, scheduler, low
70a50a3f4bSThomas Gleixner	  level interrupt handling) fully preemptible and brings most
71a50a3f4bSThomas Gleixner	  execution contexts under scheduler control.
72a50a3f4bSThomas Gleixner
73a50a3f4bSThomas Gleixner	  Select this if you are building a kernel for systems which
74a50a3f4bSThomas Gleixner	  require real-time guarantees.
75a50a3f4bSThomas Gleixner
76f8cbd99bSIngo Molnarendchoice
77cc19ca86SIngo Molnar
78bdd4e85dSFrederic Weisbeckerconfig PREEMPT_COUNT
79bdd4e85dSFrederic Weisbecker       bool
80a50a3f4bSThomas Gleixner
81b8d33498SThomas Gleixnerconfig PREEMPTION
82a50a3f4bSThomas Gleixner       bool
83a50a3f4bSThomas Gleixner       select PREEMPT_COUNT
846ef869e0SMichal Hocko
856ef869e0SMichal Hockoconfig PREEMPT_DYNAMIC
866ef869e0SMichal Hocko	bool
876ef869e0SMichal Hocko	help
886ef869e0SMichal Hocko	  This option allows to define the preemption model on the kernel
896ef869e0SMichal Hocko	  command line parameter and thus override the default preemption
906ef869e0SMichal Hocko	  model defined during compile time.
916ef869e0SMichal Hocko
926ef869e0SMichal Hocko	  The feature is primarily interesting for Linux distributions which
936ef869e0SMichal Hocko	  provide a pre-built kernel binary to reduce the number of kernel
946ef869e0SMichal Hocko	  flavors they offer while still offering different usecases.
956ef869e0SMichal Hocko
966ef869e0SMichal Hocko	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
976ef869e0SMichal Hocko	  but if runtime patching is not available for the specific architecture
986ef869e0SMichal Hocko	  then the potential overhead should be considered.
996ef869e0SMichal Hocko
1006ef869e0SMichal Hocko	  Interesting if you want the same pre-built kernel should be used for
1016ef869e0SMichal Hocko	  both Server and Desktop workloads.
102*9edeaea1SPeter Zijlstra
103*9edeaea1SPeter Zijlstraconfig SCHED_CORE
104*9edeaea1SPeter Zijlstra	bool "Core Scheduling for SMT"
105*9edeaea1SPeter Zijlstra	default y
106*9edeaea1SPeter Zijlstra	depends on SCHED_SMT
107*9edeaea1SPeter Zijlstra
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