# SPDX-License-Identifier: GPL-2.0-only

  choice
  	prompt "Preemption Model"
  	default PREEMPT_NONE
  
  config PREEMPT_NONE
  	bool "No Forced Preemption (Server)"
  	help
  	  This is the traditional Linux preemption model, geared towards
  	  throughput. It will still provide good latencies most of the
  	  time, but there are no guarantees and occasional longer delays
  	  are possible.
  
  	  Select this option if you are building a kernel for a server or
  	  scientific/computation system, or if you want to maximize the
  	  raw processing power of the kernel, irrespective of scheduling
  	  latencies.
  
  config PREEMPT_VOLUNTARY
  	bool "Voluntary Kernel Preemption (Desktop)"

  	depends on !ARCH_NO_PREEMPT

  	help

  	  This option reduces the latency of the kernel by adding more
  	  "explicit preemption points" to the kernel code. These new
  	  preemption points have been selected to reduce the maximum
  	  latency of rescheduling, providing faster application reactions,

  	  at the cost of slightly lower throughput.

  
  	  This allows reaction to interactive events by allowing a
  	  low priority process to voluntarily preempt itself even if it
  	  is in kernel mode executing a system call. This allows
  	  applications to run more 'smoothly' even when the system is

  	  under load.

  	  Select this if you are building a kernel for a desktop system.

  config PREEMPT

  	bool "Preemptible Kernel (Low-Latency Desktop)"

  	depends on !ARCH_NO_PREEMPT

  	select PREEMPTION

  	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK

  	select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC

  	help
  	  This option reduces the latency of the kernel by making
  	  all kernel code (that is not executing in a critical section)
  	  preemptible.  This allows reaction to interactive events by
  	  permitting a low priority process to be preempted involuntarily
  	  even if it is in kernel mode executing a system call and would
  	  otherwise not be about to reach a natural preemption point.
  	  This allows applications to run more 'smoothly' even when the

  	  system is under load, at the cost of slightly lower throughput

  	  and a slight runtime overhead to kernel code.
  
  	  Select this if you are building a kernel for a desktop or
  	  embedded system with latency requirements in the milliseconds
  	  range.

  config PREEMPT_RT
  	bool "Fully Preemptible Kernel (Real-Time)"
  	depends on EXPERT && ARCH_SUPPORTS_RT

  	select PREEMPTION

  	help
  	  This option turns the kernel into a real-time kernel by replacing
  	  various locking primitives (spinlocks, rwlocks, etc.) with
  	  preemptible priority-inheritance aware variants, enforcing
  	  interrupt threading and introducing mechanisms to break up long
  	  non-preemptible sections. This makes the kernel, except for very

  	  low level and critical code paths (entry code, scheduler, low

  	  level interrupt handling) fully preemptible and brings most
  	  execution contexts under scheduler control.
  
  	  Select this if you are building a kernel for systems which
  	  require real-time guarantees.

  endchoice

  config PREEMPT_COUNT

         bool

  config PREEMPTION

         bool
         select PREEMPT_COUNT

  
  config PREEMPT_DYNAMIC
  	bool
  	help
  	  This option allows to define the preemption model on the kernel
  	  command line parameter and thus override the default preemption
  	  model defined during compile time.
  
  	  The feature is primarily interesting for Linux distributions which
  	  provide a pre-built kernel binary to reduce the number of kernel
  	  flavors they offer while still offering different usecases.
  
  	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
  	  but if runtime patching is not available for the specific architecture
  	  then the potential overhead should be considered.
  
  	  Interesting if you want the same pre-built kernel should be used for
  	  both Server and Desktop workloads.

  
  config SCHED_CORE
  	bool "Core Scheduling for SMT"

  	depends on SCHED_SMT

  	help
  	  This option permits Core Scheduling, a means of coordinated task
  	  selection across SMT siblings. When enabled -- see
  	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
  	  will execute a task from the same 'core group', forcing idle when no
  	  matching task is found.
  
  	  Use of this feature includes:
  	   - mitigation of some (not all) SMT side channels;
  	   - limiting SMT interference to improve determinism and/or performance.

  	  SCHED_CORE is default disabled. When it is enabled and unused,
  	  which is the likely usage by Linux distributions, there should
  	  be no measurable impact on performance.