| # 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" |
| default y |
| 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 enabled when SCHED_SMT is enabled -- when |
| unused there should be no impact on performance. |
| |
| |