1# SPDX-License-Identifier: GPL-2.0-only 2 3config PREEMPT_NONE_BUILD 4 bool 5 6config PREEMPT_VOLUNTARY_BUILD 7 bool 8 9config PREEMPT_BUILD 10 bool 11 select PREEMPTION 12 select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK 13 14choice 15 prompt "Preemption Model" 16 default PREEMPT_NONE 17 18config PREEMPT_NONE 19 bool "No Forced Preemption (Server)" 20 select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC 21 help 22 This is the traditional Linux preemption model, geared towards 23 throughput. It will still provide good latencies most of the 24 time, but there are no guarantees and occasional longer delays 25 are possible. 26 27 Select this option if you are building a kernel for a server or 28 scientific/computation system, or if you want to maximize the 29 raw processing power of the kernel, irrespective of scheduling 30 latencies. 31 32config PREEMPT_VOLUNTARY 33 bool "Voluntary Kernel Preemption (Desktop)" 34 depends on !ARCH_NO_PREEMPT 35 select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC 36 help 37 This option reduces the latency of the kernel by adding more 38 "explicit preemption points" to the kernel code. These new 39 preemption points have been selected to reduce the maximum 40 latency of rescheduling, providing faster application reactions, 41 at the cost of slightly lower throughput. 42 43 This allows reaction to interactive events by allowing a 44 low priority process to voluntarily preempt itself even if it 45 is in kernel mode executing a system call. This allows 46 applications to run more 'smoothly' even when the system is 47 under load. 48 49 Select this if you are building a kernel for a desktop system. 50 51config PREEMPT 52 bool "Preemptible Kernel (Low-Latency Desktop)" 53 depends on !ARCH_NO_PREEMPT 54 select PREEMPT_BUILD 55 help 56 This option reduces the latency of the kernel by making 57 all kernel code (that is not executing in a critical section) 58 preemptible. This allows reaction to interactive events by 59 permitting a low priority process to be preempted involuntarily 60 even if it is in kernel mode executing a system call and would 61 otherwise not be about to reach a natural preemption point. 62 This allows applications to run more 'smoothly' even when the 63 system is under load, at the cost of slightly lower throughput 64 and a slight runtime overhead to kernel code. 65 66 Select this if you are building a kernel for a desktop or 67 embedded system with latency requirements in the milliseconds 68 range. 69 70config PREEMPT_RT 71 bool "Fully Preemptible Kernel (Real-Time)" 72 depends on EXPERT && ARCH_SUPPORTS_RT 73 select PREEMPTION 74 help 75 This option turns the kernel into a real-time kernel by replacing 76 various locking primitives (spinlocks, rwlocks, etc.) with 77 preemptible priority-inheritance aware variants, enforcing 78 interrupt threading and introducing mechanisms to break up long 79 non-preemptible sections. This makes the kernel, except for very 80 low level and critical code paths (entry code, scheduler, low 81 level interrupt handling) fully preemptible and brings most 82 execution contexts under scheduler control. 83 84 Select this if you are building a kernel for systems which 85 require real-time guarantees. 86 87endchoice 88 89config PREEMPT_COUNT 90 bool 91 92config PREEMPTION 93 bool 94 select PREEMPT_COUNT 95 96config PREEMPT_DYNAMIC 97 bool "Preemption behaviour defined on boot" 98 depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT 99 select PREEMPT_BUILD 100 default y 101 help 102 This option allows to define the preemption model on the kernel 103 command line parameter and thus override the default preemption 104 model defined during compile time. 105 106 The feature is primarily interesting for Linux distributions which 107 provide a pre-built kernel binary to reduce the number of kernel 108 flavors they offer while still offering different usecases. 109 110 The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled 111 but if runtime patching is not available for the specific architecture 112 then the potential overhead should be considered. 113 114 Interesting if you want the same pre-built kernel should be used for 115 both Server and Desktop workloads. 116 117config SCHED_CORE 118 bool "Core Scheduling for SMT" 119 depends on SCHED_SMT 120 help 121 This option permits Core Scheduling, a means of coordinated task 122 selection across SMT siblings. When enabled -- see 123 prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings 124 will execute a task from the same 'core group', forcing idle when no 125 matching task is found. 126 127 Use of this feature includes: 128 - mitigation of some (not all) SMT side channels; 129 - limiting SMT interference to improve determinism and/or performance. 130 131 SCHED_CORE is default disabled. When it is enabled and unused, 132 which is the likely usage by Linux distributions, there should 133 be no measurable impact on performance. 134 135 136