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# 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.
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