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/* * Copyright 2017 Advanced Micro Devices, Inc. * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * */ #ifndef DRM_SCHEDULER_SPSC_QUEUE_H_ #define DRM_SCHEDULER_SPSC_QUEUE_H_ #include <linux/atomic.h> #include <linux/preempt.h> /** SPSC lockless queue */ struct spsc_node { /* Stores spsc_node* */ struct spsc_node *next; }; struct spsc_queue { struct spsc_node *head; /* atomic pointer to struct spsc_node* */ atomic_long_t tail; atomic_t job_count; }; static inline void spsc_queue_init(struct spsc_queue *queue) { queue->head = NULL; atomic_long_set(&queue->tail, (long)&queue->head); atomic_set(&queue->job_count, 0); } static inline struct spsc_node *spsc_queue_peek(struct spsc_queue *queue) { return queue->head; } static inline int spsc_queue_count(struct spsc_queue *queue) { return atomic_read(&queue->job_count); } static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *node) { struct spsc_node **tail; node->next = NULL; preempt_disable(); tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next); WRITE_ONCE(*tail, node); atomic_inc(&queue->job_count); /* * In case of first element verify new node will be visible to the consumer * thread when we ping the kernel thread that there is new work to do. */ smp_wmb(); preempt_enable(); return tail == &queue->head; } static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue) { struct spsc_node *next, *node; /* Verify reading from memory and not the cache */ smp_rmb(); node = READ_ONCE(queue->head); if (!node) return NULL; next = READ_ONCE(node->next); WRITE_ONCE(queue->head, next); if (unlikely(!next)) { /* slowpath for the last element in the queue */ if (atomic_long_cmpxchg(&queue->tail, (long)&node->next, (long) &queue->head) != (long)&node->next) { /* Updating tail failed wait for new next to appear */ do { smp_rmb(); } while (unlikely(!(queue->head = READ_ONCE(node->next)))); } } atomic_dec(&queue->job_count); return node; } #endif /* DRM_SCHEDULER_SPSC_QUEUE_H_ */