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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
/*
* spin_cpu_yield may be called to yield (undirected) to the hypervisor if
* necessary. This should be used if the wait is expected to take longer
* than context switch overhead, but we can't sleep or do a directed yield.
*/
#ifndef spin_cpu_yield
#define spin_cpu_yield() cpu_relax_yield()
#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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