[PATCH v2] mbuf: add fast free bulk function

[huangdengdui]

On 2025/1/15 0:39, Morten Brørup wrote:
> mbuf: add fast free bulk function
> 
> When putting an mbuf back into its mempool, there are certain requirements
> to the mbuf. Specifically, some of its fields must be initialized.
> 
> These requirements are in fact invariants about free mbufs, held in
> mempools, and thus also apply when allocating an mbuf from a mempool.
> With this in mind, the additional assertions in rte_mbuf_raw_free() were
> moved to __rte_mbuf_raw_sanity_check().
> Furthermore, the assertion regarding pinned external buffer was enhanced;
> it now also asserts that the referenced pinned external buffer has
> refcnt == 1.
> 
> The description of RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE was updated to
> include the remaining requirements, which were missing here.
> 
> And finally:
> A new rte_mbuf_fast_free_bulk() inline function was added for the benefit
> of ethdev drivers supporting fast release of mbufs.
> It asserts these requirements and that the mbufs belong to the specified
> mempool, and then calls rte_mempool_put_bulk().
> 
> Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
> ---
> v2:
> * Fixed missing inline.
> ---
>  lib/ethdev/rte_ethdev.h |  6 ++++--
>  lib/mbuf/rte_mbuf.h     | 39 +++++++++++++++++++++++++++++++++++++--
>  2 files changed, 41 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index 1f71cad244..e9267fca79 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -1612,8 +1612,10 @@ struct rte_eth_conf {
>  #define RTE_ETH_TX_OFFLOAD_MULTI_SEGS       RTE_BIT64(15)
>  /**
>   * Device supports optimization for fast release of mbufs.
> - * When set application must guarantee that per-queue all mbufs comes from
> - * the same mempool and has refcnt = 1.
> + * When set application must guarantee that per-queue all mbufs come from the same mempool,
> + * are direct, have refcnt=1, next=NULL and nb_segs=1, as done by rte_pktmbuf_prefree_seg().
> + *
> + * @see rte_mbuf_fast_free_bulk()
>   */
>  #define RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE   RTE_BIT64(16)
>  #define RTE_ETH_TX_OFFLOAD_SECURITY         RTE_BIT64(17)
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index 0d2e0e64b3..7590d82689 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -568,6 +568,10 @@ __rte_mbuf_raw_sanity_check(__rte_unused const struct rte_mbuf *m)
>  	RTE_ASSERT(rte_mbuf_refcnt_read(m) == 1);
>  	RTE_ASSERT(m->next == NULL);
>  	RTE_ASSERT(m->nb_segs == 1);
> +	RTE_ASSERT(!RTE_MBUF_CLONED(m));
> +	RTE_ASSERT(!RTE_MBUF_HAS_EXTBUF(m) ||
> +			(RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> +			rte_mbuf_ext_refcnt_read(m->shinfo) == 1));
>  	__rte_mbuf_sanity_check(m, 0);
>  }
>  
> @@ -623,12 +627,43 @@ static inline struct rte_mbuf *rte_mbuf_raw_alloc(struct rte_mempool *mp)
>  static __rte_always_inline void
>  rte_mbuf_raw_free(struct rte_mbuf *m)
>  {
> -	RTE_ASSERT(!RTE_MBUF_CLONED(m) &&
> -		  (!RTE_MBUF_HAS_EXTBUF(m) || RTE_MBUF_HAS_PINNED_EXTBUF(m)));
>  	__rte_mbuf_raw_sanity_check(m);
>  	rte_mempool_put(m->pool, m);
>  }
>  
> +/**
> + * Put a bulk of mbufs allocated from the same mempool back into the mempool.
> + *
> + * The caller must ensure that the mbufs come from the specified mempool,
> + * are direct and properly reinitialized (refcnt=1, next=NULL, nb_segs=1), as done by
> + * rte_pktmbuf_prefree_seg().
> + *
> + * This function should be used with care, when optimization is
> + * required. For standard needs, prefer rte_pktmbuf_free_bulk().
> + *
> + * @see RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE
> + *
> + * @param mp
> + *   The mempool to which the mbufs belong.
> + * @param mbufs
> + *   Array of pointers to packet mbufs.
> + *   The array must not contain NULL pointers.
> + * @param count
> + *   Array size.
> + */
> +static __rte_always_inline void
> +rte_mbuf_fast_free_bulk(struct rte_mempool *mp, struct rte_mbuf **mbufs, unsigned int count)
> +{
> +	for (unsigned int idx = 0; idx < count; idx++) {
> +		const struct rte_mbuf *m = mbufs[idx];
> +		RTE_ASSERT(m != NULL);
> +		RTE_ASSERT(m->pool == mp);
> +		__rte_mbuf_raw_sanity_check(m);
> +	}

Is there some way to avoid executing a loop in non-debug mode? Like the following or other better way

#ifdef RTE_LIBRTE_MBUF_DEBUG
	{
		for (unsigned int idx = 0; idx < count; idx++) {
			const struct rte_mbuf *m = mbufs[idx];
			RTE_ASSERT(m != NULL);
			RTE_ASSERT(m->pool == mp);
			__rte_mbuf_raw_sanity_check(m);
		}
	}
#endif

> +
> +	rte_mempool_put_bulk(mp, (void **)mbufs, count);

Can the mp be obtained from the mbuf?

> +}
> +
>  /**
>   * The packet mbuf constructor.
>   *