--- /dev/null
+/* SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2010-2020 Intel Corporation
+ * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
+ * All rights reserved.
+ * Derived from FreeBSD's bufring.h
+ * Used as BSD-3 Licensed with permission from Kip Macy.
+ */
+
+#ifndef _RTE_RING_RTS_H_
+#define _RTE_RING_RTS_H_
+
+/**
+ * @file rte_ring_rts.h
+ * @b EXPERIMENTAL: this API may change without prior notice
+ * It is not recommended to include this file directly.
+ * Please include <rte_ring.h> instead.
+ *
+ * Contains functions for Relaxed Tail Sync (RTS) ring mode.
+ * The main idea remains the same as for our original MP/MC synchronization
+ * mechanism.
+ * The main difference is that tail value is increased not
+ * by every thread that finished enqueue/dequeue,
+ * but only by the current last one doing enqueue/dequeue.
+ * That allows threads to skip spinning on tail value,
+ * leaving actual tail value change to last thread at a given instance.
+ * RTS requires 2 64-bit CAS for each enqueue(/dequeue) operation:
+ * one for head update, second for tail update.
+ * As a gain it allows thread to avoid spinning/waiting on tail value.
+ * In comparison original MP/MC algorithm requires one 32-bit CAS
+ * for head update and waiting/spinning on tail value.
+ *
+ * Brief outline:
+ * - introduce update counter (cnt) for both head and tail.
+ * - increment head.cnt for each head.value update
+ * - write head.value and head.cnt atomically (64-bit CAS)
+ * - move tail.value ahead only when tail.cnt + 1 == head.cnt
+ * (indicating that this is the last thread updating the tail)
+ * - increment tail.cnt when each enqueue/dequeue op finishes
+ * (no matter if tail.value going to change or not)
+ * - write tail.value and tail.cnt atomically (64-bit CAS)
+ *
+ * To avoid producer/consumer starvation:
+ * - limit max allowed distance between head and tail value (HTD_MAX).
+ * I.E. thread is allowed to proceed with changing head.value,
+ * only when: head.value - tail.value <= HTD_MAX
+ * HTD_MAX is an optional parameter.
+ * With HTD_MAX == 0 we'll have fully serialized ring -
+ * i.e. only one thread at a time will be able to enqueue/dequeue
+ * to/from the ring.
+ * With HTD_MAX >= ring.capacity - no limitation.
+ * By default HTD_MAX == ring.capacity / 8.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <rte_ring_rts_c11_mem.h>
+
+/**
+ * @internal Enqueue several objects on the RTS ring.
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to add in the ring from the obj_table.
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Enqueue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
+ * @param free_space
+ * returns the amount of space after the enqueue operation has finished
+ * @return
+ * Actual number of objects enqueued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_do_rts_enqueue_elem(struct rte_ring *r, const void *obj_table,
+ uint32_t esize, uint32_t n, enum rte_ring_queue_behavior behavior,
+ uint32_t *free_space)
+{
+ uint32_t free, head;
+
+ n = __rte_ring_rts_move_prod_head(r, n, behavior, &head, &free);
+
+ if (n != 0) {
+ __rte_ring_enqueue_elems(r, head, obj_table, esize, n);
+ __rte_ring_rts_update_tail(&r->rts_prod);
+ }
+
+ if (free_space != NULL)
+ *free_space = free - n;
+ return n;
+}
+
+/**
+ * @internal Dequeue several objects from the RTS ring.
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to pull from the ring.
+ * @param behavior
+ * RTE_RING_QUEUE_FIXED: Dequeue a fixed number of items from a ring
+ * RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
+ * @param available
+ * returns the number of remaining ring entries after the dequeue has finished
+ * @return
+ * - Actual number of objects dequeued.
+ * If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_do_rts_dequeue_elem(struct rte_ring *r, void *obj_table,
+ uint32_t esize, uint32_t n, enum rte_ring_queue_behavior behavior,
+ uint32_t *available)
+{
+ uint32_t entries, head;
+
+ n = __rte_ring_rts_move_cons_head(r, n, behavior, &head, &entries);
+
+ if (n != 0) {
+ __rte_ring_dequeue_elems(r, head, obj_table, esize, n);
+ __rte_ring_rts_update_tail(&r->rts_cons);
+ }
+
+ if (available != NULL)
+ *available = entries - n;
+ return n;
+}
+
+/**
+ * Enqueue several objects on the RTS ring (multi-producers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to add in the ring from the obj_table.
+ * @param free_space
+ * if non-NULL, returns the amount of space in the ring after the
+ * enqueue operation has finished.
+ * @return
+ * The number of objects enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_mp_rts_enqueue_bulk_elem(struct rte_ring *r, const void *obj_table,
+ unsigned int esize, unsigned int n, unsigned int *free_space)
+{
+ return __rte_ring_do_rts_enqueue_elem(r, obj_table, esize, n,
+ RTE_RING_QUEUE_FIXED, free_space);
+}
+
+/**
+ * Dequeue several objects from an RTS ring (multi-consumers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects that will be filled.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to dequeue from the ring to the obj_table.
+ * @param available
+ * If non-NULL, returns the number of remaining ring entries after the
+ * dequeue has finished.
+ * @return
+ * The number of objects dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_mc_rts_dequeue_bulk_elem(struct rte_ring *r, void *obj_table,
+ unsigned int esize, unsigned int n, unsigned int *available)
+{
+ return __rte_ring_do_rts_dequeue_elem(r, obj_table, esize, n,
+ RTE_RING_QUEUE_FIXED, available);
+}
+
+/**
+ * Enqueue several objects on the RTS ring (multi-producers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to add in the ring from the obj_table.
+ * @param free_space
+ * if non-NULL, returns the amount of space in the ring after the
+ * enqueue operation has finished.
+ * @return
+ * - n: Actual number of objects enqueued.
+ */
+__rte_experimental
+static __rte_always_inline unsigned
+rte_ring_mp_rts_enqueue_burst_elem(struct rte_ring *r, const void *obj_table,
+ unsigned int esize, unsigned int n, unsigned int *free_space)
+{
+ return __rte_ring_do_rts_enqueue_elem(r, obj_table, esize, n,
+ RTE_RING_QUEUE_VARIABLE, free_space);
+}
+
+/**
+ * Dequeue several objects from an RTS ring (multi-consumers safe).
+ * When the requested objects are more than the available objects,
+ * only dequeue the actual number of objects.
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of objects that will be filled.
+ * @param esize
+ * The size of ring element, in bytes. It must be a multiple of 4.
+ * This must be the same value used while creating the ring. Otherwise
+ * the results are undefined.
+ * @param n
+ * The number of objects to dequeue from the ring to the obj_table.
+ * @param available
+ * If non-NULL, returns the number of remaining ring entries after the
+ * dequeue has finished.
+ * @return
+ * - n: Actual number of objects dequeued, 0 if ring is empty
+ */
+__rte_experimental
+static __rte_always_inline unsigned
+rte_ring_mc_rts_dequeue_burst_elem(struct rte_ring *r, void *obj_table,
+ unsigned int esize, unsigned int n, unsigned int *available)
+{
+ return __rte_ring_do_rts_dequeue_elem(r, obj_table, esize, n,
+ RTE_RING_QUEUE_VARIABLE, available);
+}
+
+/**
+ * Enqueue several objects on the RTS ring (multi-producers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of void * pointers (objects).
+ * @param n
+ * The number of objects to add in the ring from the obj_table.
+ * @param free_space
+ * if non-NULL, returns the amount of space in the ring after the
+ * enqueue operation has finished.
+ * @return
+ * The number of objects enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_mp_rts_enqueue_bulk(struct rte_ring *r, void * const *obj_table,
+ unsigned int n, unsigned int *free_space)
+{
+ return rte_ring_mp_rts_enqueue_bulk_elem(r, obj_table,
+ sizeof(uintptr_t), n, free_space);
+}
+
+/**
+ * Dequeue several objects from an RTS ring (multi-consumers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of void * pointers (objects) that will be filled.
+ * @param n
+ * The number of objects to dequeue from the ring to the obj_table.
+ * @param available
+ * If non-NULL, returns the number of remaining ring entries after the
+ * dequeue has finished.
+ * @return
+ * The number of objects dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_mc_rts_dequeue_bulk(struct rte_ring *r, void **obj_table,
+ unsigned int n, unsigned int *available)
+{
+ return rte_ring_mc_rts_dequeue_bulk_elem(r, obj_table,
+ sizeof(uintptr_t), n, available);
+}
+
+/**
+ * Enqueue several objects on the RTS ring (multi-producers safe).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of void * pointers (objects).
+ * @param n
+ * The number of objects to add in the ring from the obj_table.
+ * @param free_space
+ * if non-NULL, returns the amount of space in the ring after the
+ * enqueue operation has finished.
+ * @return
+ * - n: Actual number of objects enqueued.
+ */
+__rte_experimental
+static __rte_always_inline unsigned
+rte_ring_mp_rts_enqueue_burst(struct rte_ring *r, void * const *obj_table,
+ unsigned int n, unsigned int *free_space)
+{
+ return rte_ring_mp_rts_enqueue_burst_elem(r, obj_table,
+ sizeof(uintptr_t), n, free_space);
+}
+
+/**
+ * Dequeue several objects from an RTS ring (multi-consumers safe).
+ * When the requested objects are more than the available objects,
+ * only dequeue the actual number of objects.
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param obj_table
+ * A pointer to a table of void * pointers (objects) that will be filled.
+ * @param n
+ * The number of objects to dequeue from the ring to the obj_table.
+ * @param available
+ * If non-NULL, returns the number of remaining ring entries after the
+ * dequeue has finished.
+ * @return
+ * - n: Actual number of objects dequeued, 0 if ring is empty
+ */
+__rte_experimental
+static __rte_always_inline unsigned
+rte_ring_mc_rts_dequeue_burst(struct rte_ring *r, void **obj_table,
+ unsigned int n, unsigned int *available)
+{
+ return rte_ring_mc_rts_dequeue_burst_elem(r, obj_table,
+ sizeof(uintptr_t), n, available);
+}
+
+/**
+ * Return producer max Head-Tail-Distance (HTD).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @return
+ * Producer HTD value, if producer is set in appropriate sync mode,
+ * or UINT32_MAX otherwise.
+ */
+__rte_experimental
+static inline uint32_t
+rte_ring_get_prod_htd_max(const struct rte_ring *r)
+{
+ if (r->prod.sync_type == RTE_RING_SYNC_MT_RTS)
+ return r->rts_prod.htd_max;
+ return UINT32_MAX;
+}
+
+/**
+ * Set producer max Head-Tail-Distance (HTD).
+ * Note that producer has to use appropriate sync mode (RTS).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param v
+ * new HTD value to setup.
+ * @return
+ * Zero on success, or negative error code otherwise.
+ */
+__rte_experimental
+static inline int
+rte_ring_set_prod_htd_max(struct rte_ring *r, uint32_t v)
+{
+ if (r->prod.sync_type != RTE_RING_SYNC_MT_RTS)
+ return -ENOTSUP;
+
+ r->rts_prod.htd_max = v;
+ return 0;
+}
+
+/**
+ * Return consumer max Head-Tail-Distance (HTD).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @return
+ * Consumer HTD value, if consumer is set in appropriate sync mode,
+ * or UINT32_MAX otherwise.
+ */
+__rte_experimental
+static inline uint32_t
+rte_ring_get_cons_htd_max(const struct rte_ring *r)
+{
+ if (r->cons.sync_type == RTE_RING_SYNC_MT_RTS)
+ return r->rts_cons.htd_max;
+ return UINT32_MAX;
+}
+
+/**
+ * Set consumer max Head-Tail-Distance (HTD).
+ * Note that consumer has to use appropriate sync mode (RTS).
+ *
+ * @param r
+ * A pointer to the ring structure.
+ * @param v
+ * new HTD value to setup.
+ * @return
+ * Zero on success, or negative error code otherwise.
+ */
+__rte_experimental
+static inline int
+rte_ring_set_cons_htd_max(struct rte_ring *r, uint32_t v)
+{
+ if (r->cons.sync_type != RTE_RING_SYNC_MT_RTS)
+ return -ENOTSUP;
+
+ r->rts_cons.htd_max = v;
+ return 0;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_RING_RTS_H_ */
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