| /* SPDX-License-Identifier: GPL-2.0 */ |
| /* Misc low level processor primitives */ |
| #ifndef _LINUX_PROCESSOR_H |
| #define _LINUX_PROCESSOR_H |
| |
| #include <asm/processor.h> |
| |
| /* |
| * spin_begin is used before beginning a busy-wait loop, and must be paired |
| * with spin_end when the loop is exited. spin_cpu_relax must be called |
| * within the loop. |
| * |
| * The loop body should be as small and fast as possible, on the order of |
| * tens of instructions/cycles as a guide. It should and avoid calling |
| * cpu_relax, or any "spin" or sleep type of primitive including nested uses |
| * of these primitives. It should not lock or take any other resource. |
| * Violations of these guidelies will not cause a bug, but may cause sub |
| * optimal performance. |
| * |
| * These loops are optimized to be used where wait times are expected to be |
| * less than the cost of a context switch (and associated overhead). |
| * |
| * Detection of resource owner and decision to spin or sleep or guest-yield |
| * (e.g., spin lock holder vcpu preempted, or mutex owner not on CPU) can be |
| * tested within the loop body. |
| */ |
| #ifndef spin_begin |
| #define spin_begin() |
| #endif |
| |
| #ifndef spin_cpu_relax |
| #define spin_cpu_relax() cpu_relax() |
| #endif |
| |
| #ifndef spin_end |
| #define spin_end() |
| #endif |
| |
| /* |
| * spin_until_cond can be used to wait for a condition to become true. It |
| * may be expected that the first iteration will true in the common case |
| * (no spinning), so that callers should not require a first "likely" test |
| * for the uncontended case before using this primitive. |
| * |
| * Usage and implementation guidelines are the same as for the spin_begin |
| * primitives, above. |
| */ |
| #ifndef spin_until_cond |
| #define spin_until_cond(cond) \ |
| do { \ |
| if (unlikely(!(cond))) { \ |
| spin_begin(); \ |
| do { \ |
| spin_cpu_relax(); \ |
| } while (!(cond)); \ |
| spin_end(); \ |
| } \ |
| } while (0) |
| |
| #endif |
| |
| #endif /* _LINUX_PROCESSOR_H */ |