[dpdk-dev] [RFC] mbuf: rte_pktmbuf_free() optimized for multi-seg packets

["Morten Brørup" <mb@smartsharesystems.com>]

Hi all,

The rte_pktmbuf_free() function could be optimized by freeing multiple segments in bulk using rte_mempool_put_bulk().

I got this idea while optimizing the rte_pktmbuf_free_bulk() function similarly, as suggested by Stephen Hemminger and Konstantin Ananyev.


If any of you DPDK performance freaks want to test this concept, here's some source code to get you started.


/**
 * @internal Size of the array holding mbufs from the same membool to be freed
 * in bulk.
 */
#define RTE_PKTMBUF_FREE_BULK_SZ 64

/**
 * @internal helper function for freeing a bulk of mbufs via an array holding
 * mbufs from the same mempool.
 */
static __rte_always_inline void
rte_pktmbuf_free_seg_via_array(struct rte_mbuf *m,
	struct rte_mbuf * * const free, unsigned int * const nb_free)
{
	m = rte_pktmbuf_prefree_seg(m);
	if (likely(m != NULL)) {
		if (*nb_free >= RTE_PKTMBUF_FREE_BULK_SZ ||
		    (*nb_free > 0 && m->pool != free[0]->pool)) {
			rte_mempool_put_bulk(free[0]->pool, (void **)free,
					     *nb_free);
			*nb_free = 0;
		}

		free[(*nb_free)++] = m;
	}
}

/**
 * Free a packet mbuf back into its original mempool.
 *
 * Free an mbuf, and all its segments in case of chained buffers. Each
 * segment is added back into its original mempool.
 *
 * @param m
 *   The packet mbuf to be freed. If NULL, the function does nothing.
 */
static inline void rte_pktmbuf_free(struct rte_mbuf *m)
{
	struct rte_mbuf *m_next, *free[RTE_PKTMBUF_FREE_BULK_SZ];
	unsigned int nb_free = 0;

	if (unlikely(m == NULL)) return;

	__rte_mbuf_sanity_check(m, 1);

	do {
		m_next = m->next;
		rte_pktmbuf_free_seg_via_array(m, free, &nb_free);
		m = m_next;
	} while (m != NULL);

	if (nb_free > 0)
		rte_mempool_put_bulk(free[0]->pool, (void **)free, nb_free);
}


Med venlig hilsen / kind regards

Morten Brørup
CTO


SmartShare Systems A/S
Tonsbakken 16-18
DK-2740 Skovlunde
Denmark

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mb@smartsharesystems.com
www.smartsharesystems.com