rte_ring_generic.h

/* SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2010-2017 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_GENERIC_H_
#define _RTE_RING_GENERIC_H_

static __rte_always_inline void
update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
                uint32_t single, uint32_t enqueue)
{
        if (enqueue)
                rte_smp_wmb();
        else
                rte_smp_rmb();
        /*
         * If there are other enqueues/dequeues in progress that preceded us,
         * we need to wait for them to complete
         */
        if (!single)
                while (unlikely(ht->tail != old_val))
                        rte_pause();

        ht->tail = new_val;
}

static __rte_always_inline unsigned int
__rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
                unsigned int n, enum rte_ring_queue_behavior behavior,
                uint32_t *old_head, uint32_t *new_head,
                uint32_t *free_entries)
{
        const uint32_t capacity = r->capacity;
        unsigned int max = n;
        int success;

        do {
                /* Reset n to the initial burst count */
                n = max;

                *old_head = r->prod.head;

                /* add rmb barrier to avoid load/load reorder in weak
                 * memory model. It is noop on x86
                 */
                rte_smp_rmb();

                /*
                 *  The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * *old_head > cons_tail). So 'free_entries' is always between 0
                 * and capacity (which is < size).
                 */
                *free_entries = (capacity + r->cons.tail - *old_head);

                /* check that we have enough room in ring */
                if (unlikely(n > *free_entries))
                        n = (behavior == RTE_RING_QUEUE_FIXED) ?
                                        0 : *free_entries;

                if (n == 0)
                        return 0;

                *new_head = *old_head + n;
                if (is_sp)
                        r->prod.head = *new_head, success = 1;
                else
                        success = rte_atomic32_cmpset(&r->prod.head,
                                        *old_head, *new_head);
        } while (unlikely(success == 0));
        return n;
}

static __rte_always_inline unsigned int
__rte_ring_move_cons_head(struct rte_ring *r, unsigned int is_sc,
                unsigned int n, enum rte_ring_queue_behavior behavior,
                uint32_t *old_head, uint32_t *new_head,
                uint32_t *entries)
{
        unsigned int max = n;
        int success;

        /* move cons.head atomically */
        do {
                /* Restore n as it may change every loop */
                n = max;

                *old_head = r->cons.head;

                /* add rmb barrier to avoid load/load reorder in weak
                 * memory model. It is noop on x86
                 */
                rte_smp_rmb();

                /* The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * cons_head > prod_tail). So 'entries' is always between 0
                 * and size(ring)-1.
                 */
                *entries = (r->prod.tail - *old_head);

                /* Set the actual entries for dequeue */
                if (n > *entries)
                        n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;

                if (unlikely(n == 0))
                        return 0;

                *new_head = *old_head + n;
                if (is_sc) {
                        r->cons.head = *new_head;
                        rte_smp_rmb();
                        success = 1;
                } else {
                        success = rte_atomic32_cmpset(&r->cons.head, *old_head,
                                        *new_head);
                }
        } while (unlikely(success == 0));
        return n;
}

#endif /* _RTE_RING_GENERIC_H_ */