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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125/* * 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();
atomic_inc(&queue->job_count); smp_mb__after_atomic();
tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next); WRITE_ONCE(*tail, node);
/* * 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_ */