> From: Bruce Richardson [mailto:[email protected]] > Sent: Friday, 10 October 2025 09.44 > > On Thu, Oct 09, 2025 at 07:35:54PM +0200, Morten Brørup wrote: > > > From: Bruce Richardson [mailto:[email protected]] > > > Sent: Thursday, 9 October 2025 19.15 > > > > > > 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. > > > > The code is basically copy-paste from rte_pktmbuf_reset(). > > I kept it the same way for readability. > > > > I'd think using 64-bit stores should be fine for readability so long as > there is a comment on each one (maybe with compile-time checks for > field > layout).
OK. I'll put this additional optimization on my TODO list for later, and will do it for both rte_mbuf_raw_reset_bulk() and rte_pktmbuf_reset(). I'm too busy with another project to do it now. > > > > 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. > > > > Yes, I have given the concept a lot of thought already. > > If we didn't require mbufs residing in the mempool to have any fields > initialized, specifically "next" and "nb_segs", it would improve > performance for drivers freeing mbufs back to the mempool, because > writing to the mbufs would no longer be required at that point; the > mbufs could simply be freed back to the mempool. Instead, we would > require the driver to initialize these fields - which it probably does > on RX anyway, if it supports segmented packets. > > But I consider this concept a major API change, also affecting > applications assuming that these fields are initialized when allocating > raw mbufs from the mempool. So I haven't pursued it. > > > Yes, agreed. Let's not change anything in those restrictions. Maybe later, if the tech board agrees to such a change. > > /Bruce
