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
  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