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 PREEMPT_BUILD
 100         default y
 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.
 116
 117 config SCHED_CORE
 118         bool "Core Scheduling for SMT"
 119         depends on SCHED_SMT
 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
 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.
 134
 135