> From: Thomas Monjalon [mailto:tho...@monjalon.net] > Sent: Saturday, November 7, 2020 4:53 PM > > The mempool pointer in the mbuf struct is moved > from the second to the first half. > It should increase performance on most systems having 64-byte cache line, > i.e. mbuf is split in two cache lines.
Perhaps with the #define DEV_TX_OFFLOAD_MBUF_FAST_FREE mentioned by Konstantin, it might be better moving m->next instead, at least for applications with the opportunity to set this flag (e.g. applications with only one mbuf pool). Unfortunately, the information about the DEV_TX_OFFLOAD_MBUF_FAST_FREE flag came to light after the techboard meeting, and I don't have any benchmarks to support this suggestion, so I guess it's hard to change the techboard's decision to move the pool pointer. > > Due to this change, tx_offload is moved, so some vector data paths > may need to be adjusted. Note: OCTEON TX2 check is removed temporarily! Regardless if m->pool or m->next is moved, it will not affect any issues related to m->tx_offload moving to a new location in the second cache line. > > Moving this field gives more space to dynfield1. > > This is how the mbuf layout looks like (pahole-style): > > word type name byte size > 0 void * buf_addr; /* 0 + 8 */ > 1 rte_iova_t buf_iova /* 8 + 8 */ > /* --- RTE_MARKER64 rearm_data; */ > 2 uint16_t data_off; /* 16 + 2 */ > uint16_t refcnt; /* 18 + 2 */ > uint16_t nb_segs; /* 20 + 2 */ > uint16_t port; /* 22 + 2 */ > 3 uint64_t ol_flags; /* 24 + 8 */ > /* --- RTE_MARKER rx_descriptor_fields1; */ > 4 uint32_t union packet_type; /* 32 + 4 */ > uint32_t pkt_len; /* 36 + 4 */ > 5 uint16_t data_len; /* 40 + 2 */ > uint16_t vlan_tci; /* 42 + 2 */ > 5.5 uint64_t union hash; /* 44 + 8 */ > 6.5 uint16_t vlan_tci_outer; /* 52 + 2 */ > uint16_t buf_len; /* 54 + 2 */ > 7 struct rte_mempool * pool; /* 56 + 8 */ > /* --- RTE_MARKER cacheline1; */ > 8 struct rte_mbuf * next; /* 64 + 8 */ > 9 uint64_t union tx_offload; /* 72 + 8 */ > 10 struct rte_mbuf_ext_shared_info * shinfo; /* 80 + 8 */ > 11 uint16_t priv_size; /* 88 + 2 */ > uint16_t timesync; /* 90 + 2 */ > 11.5 uint32_t dynfield1[9]; /* 92 + 36 */ > 16 /* --- END 128 */ > > Signed-off-by: Thomas Monjalon <tho...@monjalon.net> > --- > doc/guides/rel_notes/deprecation.rst | 7 ------- > drivers/net/octeontx2/otx2_ethdev.c | 2 -- > lib/librte_kni/rte_kni_common.h | 3 ++- > lib/librte_mbuf/rte_mbuf.h | 1 - > lib/librte_mbuf/rte_mbuf_core.h | 5 ++--- > lib/librte_mbuf/rte_mbuf_dyn.c | 1 - > 6 files changed, 4 insertions(+), 15 deletions(-) > > diff --git a/doc/guides/rel_notes/deprecation.rst > b/doc/guides/rel_notes/deprecation.rst > index f3258eb3f7..efb09f0c5e 100644 > --- a/doc/guides/rel_notes/deprecation.rst > +++ b/doc/guides/rel_notes/deprecation.rst > @@ -81,13 +81,6 @@ Deprecation Notices > us extending existing enum/define. > One solution can be using a fixed size array instead of ``.*MAX.*`` > value. > > -* mbuf: Some fields will be converted to dynamic API in DPDK 20.11 > - in order to reserve more space for the dynamic fields, as explained in > - `this presentation <https://www.youtube.com/watch?v=Ttl6MlhmzWY>`_. > - As a consequence, the layout of the ``struct rte_mbuf`` will be re- > arranged, > - avoiding impact on vectorized implementation of the driver datapaths, > - while evaluating performance gains of a better use of the first cache > line. > - > * ethdev: The flow director API, including ``rte_eth_conf.fdir_conf`` > field, > and the related structures (``rte_fdir_*`` and ``rte_eth_fdir_*``), > will be removed in DPDK 20.11. > diff --git a/drivers/net/octeontx2/otx2_ethdev.c > b/drivers/net/octeontx2/otx2_ethdev.c > index 6cebbe677d..d6e0f1dd03 100644 > --- a/drivers/net/octeontx2/otx2_ethdev.c > +++ b/drivers/net/octeontx2/otx2_ethdev.c > @@ -748,8 +748,6 @@ nix_tx_offload_flags(struct rte_eth_dev *eth_dev) > offsetof(struct rte_mbuf, buf_iova) + 16); > RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, pkt_len) != > offsetof(struct rte_mbuf, ol_flags) + 12); > - RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, tx_offload) != > - offsetof(struct rte_mbuf, pool) + 2 * sizeof(void *)); > > if (conf & DEV_TX_OFFLOAD_VLAN_INSERT || > conf & DEV_TX_OFFLOAD_QINQ_INSERT) > diff --git a/lib/librte_kni/rte_kni_common.h > b/lib/librte_kni/rte_kni_common.h > index 36d66e2ffa..ffb3182731 100644 > --- a/lib/librte_kni/rte_kni_common.h > +++ b/lib/librte_kni/rte_kni_common.h > @@ -84,10 +84,11 @@ struct rte_kni_mbuf { > char pad2[4]; > uint32_t pkt_len; /**< Total pkt len: sum of all segment > data_len. */ > uint16_t data_len; /**< Amount of data in segment buffer. */ > + char pad3[14]; > + void *pool; > > /* fields on second cache line */ > __attribute__((__aligned__(RTE_CACHE_LINE_MIN_SIZE))) > - void *pool; > void *next; /**< Physical address of next mbuf in kernel. > */ > }; > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h > index 3190a29cce..c4c9ebfaa0 100644 > --- a/lib/librte_mbuf/rte_mbuf.h > +++ b/lib/librte_mbuf/rte_mbuf.h > @@ -1107,7 +1107,6 @@ rte_pktmbuf_attach_extbuf(struct rte_mbuf *m, void > *buf_addr, > static inline void > rte_mbuf_dynfield_copy(struct rte_mbuf *mdst, const struct rte_mbuf *msrc) > { > - memcpy(&mdst->dynfield0, msrc->dynfield0, sizeof(mdst->dynfield0)); > memcpy(&mdst->dynfield1, msrc->dynfield1, sizeof(mdst->dynfield1)); > } > > diff --git a/lib/librte_mbuf/rte_mbuf_core.h > b/lib/librte_mbuf/rte_mbuf_core.h > index debaace95a..567551deab 100644 > --- a/lib/librte_mbuf/rte_mbuf_core.h > +++ b/lib/librte_mbuf/rte_mbuf_core.h > @@ -586,12 +586,11 @@ struct rte_mbuf { > > uint16_t buf_len; /**< Length of segment buffer. */ > > - uint64_t dynfield0[1]; /**< Reserved for dynamic fields. */ > + struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */ > > /* second cache line - fields only used in slow path or on TX */ > RTE_MARKER cacheline1 __rte_cache_min_aligned; > > - struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */ > struct rte_mbuf *next; /**< Next segment of scattered packet. */ > > /* fields to support TX offloads */ > @@ -645,7 +644,7 @@ struct rte_mbuf { > /** Timesync flags for use with IEEE1588. */ > uint16_t timesync; > > - uint32_t dynfield1[7]; /**< Reserved for dynamic fields. */ > + uint32_t dynfield1[9]; /**< Reserved for dynamic fields. */ > } __rte_cache_aligned; > > /** > diff --git a/lib/librte_mbuf/rte_mbuf_dyn.c > b/lib/librte_mbuf/rte_mbuf_dyn.c > index fd3e019a22..7d5e942bf0 100644 > --- a/lib/librte_mbuf/rte_mbuf_dyn.c > +++ b/lib/librte_mbuf/rte_mbuf_dyn.c > @@ -125,7 +125,6 @@ init_shared_mem(void) > * rte_mbuf_dynfield_copy(). > */ > memset(shm, 0, sizeof(*shm)); > - mark_free(dynfield0); > mark_free(dynfield1); > > /* init free_flags */ > -- > 2.28.0 >
