[dpdk-dev] [PATCH 1/1] mbuf: move pool pointer in first half

[Thomas Monjalon <thomas@monjalon.net>]

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.

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!

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@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