[dpdk-dev] [PATCH 1/1] mbuf: move pool pointer in first half
Morten Brørup
mb at smartsharesystems.com
Sat Nov 7 19:57:05 CET 2020
> From: Thomas Monjalon [mailto:thomas at 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 <thomas at 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
>
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