On Sat, Aug 23, 2025 at 06:30:02AM +0000, Morten Brørup wrote: > An optimized function for resetting a bulk of newly allocated > reinitialized mbufs (a.k.a. raw mbufs) was added. > > Compared to the normal packet mbuf reset function, it takes advantage of > the following two details: > 1. The 'next' and 'nb_segs' fields are already reset, so resetting them > has been omitted. > 2. When resetting the mbuf, the 'ol_flags' field must indicate whether the > mbuf uses an external buffer, and the 'data_off' field must not exceed the > data room size when resetting the data offset to include the default > headroom. > Unlike the normal packet mbuf reset function, which reads the mbuf itself > to get the information required for resetting these two fields, this > function gets the information from the mempool. > > This makes the function write-only of the mbuf, unlike the normal packet > mbuf reset function, which is read-modify-write of the mbuf. > > Signed-off-by: Morten Brørup <[email protected]> > --- > lib/mbuf/rte_mbuf.h | 74 ++++++++++++++++++++++++++++----------------- > 1 file changed, 46 insertions(+), 28 deletions(-) > > diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h > index 49c93ab356..6f37a2e91e 100644 > --- a/lib/mbuf/rte_mbuf.h > +++ b/lib/mbuf/rte_mbuf.h > @@ -954,6 +954,50 @@ static inline void rte_pktmbuf_reset_headroom(struct > rte_mbuf *m) > (uint16_t)m->buf_len); > } > > +/** > + * Reset the fields of a bulk of packet mbufs to their default values. > + * > + * 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_reset(). > + * > + * @param mp > + * The mempool to which the mbuf belongs. > + * @param mbufs > + * Array of pointers to packet mbufs. > + * The array must not contain NULL pointers. > + * @param count > + * Array size. > + */ > +static inline void > +rte_mbuf_raw_reset_bulk(struct rte_mempool *mp, struct rte_mbuf **mbufs, > unsigned int count) > +{ > + uint64_t ol_flags = (rte_pktmbuf_priv_flags(mp) & > RTE_PKTMBUF_POOL_F_PINNED_EXT_BUF) ? > + RTE_MBUF_F_EXTERNAL : 0; > + uint16_t data_off = RTE_MIN_T(RTE_PKTMBUF_HEADROOM, > rte_pktmbuf_data_room_size(mp), > + uint16_t); > + > + for (unsigned int idx = 0; idx < count; idx++) { > + struct rte_mbuf *m = mbufs[idx]; > + > + m->pkt_len = 0; > + m->tx_offload = 0; > + m->vlan_tci = 0; > + m->vlan_tci_outer = 0; > + m->port = RTE_MBUF_PORT_INVALID;
Have you considered doing all initialization using 64-bit stores? It's generally cheaper to do a single 64-bit store than e.g. set of 16-bit ones. This also means that we could remove the restriction on having refcnt and nb_segs already set. As in PMDs, a single store can init data_off, ref_cnt, nb_segs and port. Similarly for packet_type and pkt_len, and data_len/vlan_tci and rss fields etc. For max performance, the whole of the mbuf cleared here can be done in 40 bytes, or 5 64-bit stores. If we do the stores in order, possibly the compiler can even opportunistically coalesce more stores, so we could even end up getting 128-bit or larger stores depending on the ISA compiled for. [Maybe the compiler will do this even if they are not in order, but I'd like to maximize my chances here! :-)] /Bruce > + > + m->ol_flags = ol_flags; > + m->packet_type = 0; > + m->data_off = data_off; > + > + m->data_len = 0; > + __rte_mbuf_sanity_check(m, 1); > + } > +} > + <snip>
