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