/* * 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
/* * 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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