kernel/Kconfig.preempt

   1 # SPDX-License-Identifier: GPL-2.0-only
   2
   3 config PREEMPT_NONE_BUILD
   4         bool
   5
   6 config PREEMPT_VOLUNTARY_BUILD
   7         bool
   8
   9 config PREEMPT_BUILD
  10         bool
  11         select PREEMPTION
  12         select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
  13
  14 choice
  15         prompt "Preemption Model"
  16         default PREEMPT_NONE
  17
  18 config 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
  32 config 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
  51 config 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
  70 config 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
  87 endchoice
  88
  89 config PREEMPT_COUNT
  90        bool
  91
  92 config PREEMPTION
  93        bool
  94        select PREEMPT_COUNT
  95
  96 config 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
 118 config 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