numam-dpdk/lib/librte_ring/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;
}

/**
 * @internal This function updates the producer head for enqueue
 *
 * @param r
 *   A pointer to the ring structure
 * @param is_sp
 *   Indicates whether multi-producer path is needed or not
 * @param n
 *   The number of elements we will want to enqueue, i.e. how far should the
 *   head be moved
 * @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 old_head
 *   Returns head value as it was before the move, i.e. where enqueue starts
 * @param new_head
 *   Returns the current/new head value i.e. where enqueue finishes
 * @param free_entries
 *   Returns the amount of free space in the ring BEFORE head was moved
 * @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_move_prod_head(struct rte_ring *r, 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();

		const uint32_t cons_tail = r->cons.tail;
		/*
		 *  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 + 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;
}

/**
 * @internal This function updates the consumer head for dequeue
 *
 * @param r
 *   A pointer to the ring structure
 * @param is_sc
 *   Indicates whether multi-consumer path is needed or not
 * @param n
 *   The number of elements we will want to enqueue, i.e. how far should the
 *   head be moved
 * @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 old_head
 *   Returns head value as it was before the move, i.e. where dequeue starts
 * @param new_head
 *   Returns the current/new head value i.e. where dequeue finishes
 * @param entries
 *   Returns the number of entries in the ring BEFORE head was moved
 * @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_move_cons_head(struct rte_ring *r, 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();

		const uint32_t prod_tail = r->prod.tail;
		/* 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 = (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, 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_ */