It is intended to sabstitute the bounded fifo we are currently
using.
Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
---
drivers/gpu/drm/amd/scheduler/spsc_queue.h | 120 +++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
create mode 100644 drivers/gpu/drm/amd/scheduler/spsc_queue.h
diff --git a/drivers/gpu/drm/amd/scheduler/spsc_queue.h b/drivers/gpu/drm/amd/scheduler/spsc_queue.h
new file mode 100644
index 0000000..a3394f1
--- /dev/null
+++ b/drivers/gpu/drm/amd/scheduler/spsc_queue.h
@@ -0,0 +1,120 @@
+/*
+ * 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 AMD_SCHEDULER_SPSC_QUEUE_H_
+#define AMD_SCHEDULER_SPSC_QUEUE_H_
+
+#include <linux/atomic.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 /* AMD_SCHEDULER_SPSC_QUEUE_H_ */
--
2.7.4
