1193156Snwhitehorn/* SPDX-License-Identifier: GPL-2.0 */ 2193156Snwhitehorn/* Misc low level processor primitives */ 3193156Snwhitehorn#ifndef _LINUX_PROCESSOR_H 4193156Snwhitehorn#define _LINUX_PROCESSOR_H 5193156Snwhitehorn 6193156Snwhitehorn#include <asm/processor.h> 7193156Snwhitehorn 8193156Snwhitehorn/* 9193156Snwhitehorn * spin_begin is used before beginning a busy-wait loop, and must be paired 10193156Snwhitehorn * with spin_end when the loop is exited. spin_cpu_relax must be called 11193156Snwhitehorn * within the loop. 12193156Snwhitehorn * 13193156Snwhitehorn * The loop body should be as small and fast as possible, on the order of 14193156Snwhitehorn * tens of instructions/cycles as a guide. It should and avoid calling 15193156Snwhitehorn * cpu_relax, or any "spin" or sleep type of primitive including nested uses 16193156Snwhitehorn * of these primitives. It should not lock or take any other resource. 17193156Snwhitehorn * Violations of these guidelies will not cause a bug, but may cause sub 18193156Snwhitehorn * optimal performance. 19193156Snwhitehorn * 20193156Snwhitehorn * These loops are optimized to be used where wait times are expected to be 21193156Snwhitehorn * less than the cost of a context switch (and associated overhead). 22193156Snwhitehorn * 23193156Snwhitehorn * Detection of resource owner and decision to spin or sleep or guest-yield 24193156Snwhitehorn * (e.g., spin lock holder vcpu preempted, or mutex owner not on CPU) can be 25193156Snwhitehorn * tested within the loop body. 26193156Snwhitehorn */ 27193156Snwhitehorn#ifndef spin_begin 28193156Snwhitehorn#define spin_begin() 29193156Snwhitehorn#endif 30193156Snwhitehorn 31193156Snwhitehorn#ifndef spin_cpu_relax 32193156Snwhitehorn#define spin_cpu_relax() cpu_relax() 33193156Snwhitehorn#endif 34193156Snwhitehorn 35193156Snwhitehorn#ifndef spin_end 36193156Snwhitehorn#define spin_end() 37193156Snwhitehorn#endif 38193156Snwhitehorn 39193156Snwhitehorn/* 40193156Snwhitehorn * spin_until_cond can be used to wait for a condition to become true. It 41193156Snwhitehorn * may be expected that the first iteration will true in the common case 42193156Snwhitehorn * (no spinning), so that callers should not require a first "likely" test 43193156Snwhitehorn * for the uncontended case before using this primitive. 44193156Snwhitehorn * 45193156Snwhitehorn * Usage and implementation guidelines are the same as for the spin_begin 46193156Snwhitehorn * primitives, above. 47193156Snwhitehorn */ 48193156Snwhitehorn#ifndef spin_until_cond 49193156Snwhitehorn#define spin_until_cond(cond) \ 50193156Snwhitehorndo { \ 51193156Snwhitehorn if (unlikely(!(cond))) { \ 52193156Snwhitehorn spin_begin(); \ 53193156Snwhitehorn do { \ 54193156Snwhitehorn spin_cpu_relax(); \ 55193156Snwhitehorn } while (!(cond)); \ 56193156Snwhitehorn spin_end(); \ 57193156Snwhitehorn } \ 58193156Snwhitehorn} while (0) 59193156Snwhitehorn 60193156Snwhitehorn#endif 61193156Snwhitehorn 62193156Snwhitehorn#endif /* _LINUX_PROCESSOR_H */ 63193156Snwhitehorn