LXR linux/kernel/Kconfig.preempt

   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
 122