rte_ring_hts_c11_mem.h

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/* 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_HTS_C11_MEM_H_
#define _RTE_RING_HTS_C11_MEM_H_

static __rte_always_inline void
__rte_ring_hts_update_tail(struct rte_ring_hts_headtail *ht, uint32_t old_tail,
    uint32_t num, uint32_t enqueue)
{
    uint32_t tail;

    RTE_SET_USED(enqueue);

    tail = old_tail + num;
    __atomic_store_n(&ht->ht.pos.tail, tail, __ATOMIC_RELEASE);
}

static __rte_always_inline void
__rte_ring_hts_head_wait(const struct rte_ring_hts_headtail *ht,
        union __rte_ring_hts_pos *p)
{
    while (p->pos.head != p->pos.tail) {
        rte_pause();
        p->raw = __atomic_load_n(&ht->ht.raw, __ATOMIC_ACQUIRE);
    }
}

static __rte_always_inline unsigned int
__rte_ring_hts_move_prod_head(struct rte_ring *r, unsigned int num,
    enum rte_ring_queue_behavior behavior, uint32_t *old_head,
    uint32_t *free_entries)
{
    uint32_t n;
    union __rte_ring_hts_pos np, op;

    const uint32_t capacity = r->capacity;

    op.raw = __atomic_load_n(&r->hts_prod.ht.raw, __ATOMIC_ACQUIRE);

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

        /*
         * wait for tail to be equal to head,
         * make sure that we read prod head/tail *before*
         * reading cons tail.
         */
        __rte_ring_hts_head_wait(&r->hts_prod, &op);

        /*
         *  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 - op.pos.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)
            break;

        np.pos.tail = op.pos.tail;
        np.pos.head = op.pos.head + n;

    /*
     * this CAS(ACQUIRE, ACQUIRE) serves as a hoist barrier to prevent:
     *  - OOO reads of cons tail value
     *  - OOO copy of elems from the ring
     */
    } while (__atomic_compare_exchange_n(&r->hts_prod.ht.raw,
            &op.raw, np.raw,
            0, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE) == 0);

    *old_head = op.pos.head;
    return n;
}

static __rte_always_inline unsigned int
__rte_ring_hts_move_cons_head(struct rte_ring *r, unsigned int num,
    enum rte_ring_queue_behavior behavior, uint32_t *old_head,
    uint32_t *entries)
{
    uint32_t n;
    union __rte_ring_hts_pos np, op;

    op.raw = __atomic_load_n(&r->hts_cons.ht.raw, __ATOMIC_ACQUIRE);

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

        /*
         * wait for tail to be equal to head,
         * make sure that we read cons head/tail *before*
         * reading prod tail.
         */
        __rte_ring_hts_head_wait(&r->hts_cons, &op);

        /* 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 - op.pos.head;

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

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

        np.pos.tail = op.pos.tail;
        np.pos.head = op.pos.head + n;

    /*
     * this CAS(ACQUIRE, ACQUIRE) serves as a hoist barrier to prevent:
     *  - OOO reads of prod tail value
     *  - OOO copy of elems from the ring
     */
    } while (__atomic_compare_exchange_n(&r->hts_cons.ht.raw,
            &op.raw, np.raw,
            0, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE) == 0);

    *old_head = op.pos.head;
    return n;
}

#endif /* _RTE_RING_HTS_C11_MEM_H_ */