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- /* 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 */
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