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