[dpdk-dev] [PATCH] mbuf: add helpers to prefetch mbuf

[Olivier Matz]

Some architectures (ex: Power8) have a cache line size of 128 bytes,
so the drivers should not expect that prefetching the second part of
the mbuf is valid.

This commit add helpers that can be used by drivers to prefetch the
rx or tx part of the mbuf, whatever the cache line size.

Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
---
 drivers/net/fm10k/fm10k_rxtx_vec.c |  8 ++++----
 drivers/net/i40e/i40e_rxtx_vec.c   |  8 ++++----
 drivers/net/ixgbe/ixgbe_rxtx_vec.c |  8 ++++----
 drivers/net/mlx4/mlx4.c            |  4 ++--
 drivers/net/mlx5/mlx5_rxtx.c       |  4 ++--
 examples/ipsec-secgw/ipsec-secgw.c |  2 +-
 lib/librte_mbuf/rte_mbuf.h         | 38 ++++++++++++++++++++++++++++++++++++++
 7 files changed, 55 insertions(+), 17 deletions(-)

diff --git a/drivers/net/fm10k/fm10k_rxtx_vec.c b/drivers/net/fm10k/fm10k_rxtx_vec.c
index f8efe8f..2f3ccfe 100644
--- a/drivers/net/fm10k/fm10k_rxtx_vec.c
+++ b/drivers/net/fm10k/fm10k_rxtx_vec.c
@@ -487,10 +487,10 @@ fm10k_recv_raw_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
 		rte_compiler_barrier();
 
 		if (split_packet) {
-			rte_prefetch0(&rx_pkts[pos]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 1]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 2]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 3]->cacheline1);
+			rte_mbuf_prefetch_part1(rx_pkts[pos]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 1]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 2]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 3]);
 		}
 
 		/* D.1 pkt 3,4 convert format from desc to pktmbuf */
diff --git a/drivers/net/i40e/i40e_rxtx_vec.c b/drivers/net/i40e/i40e_rxtx_vec.c
index 047aff5..ac528c4 100644
--- a/drivers/net/i40e/i40e_rxtx_vec.c
+++ b/drivers/net/i40e/i40e_rxtx_vec.c
@@ -331,10 +331,10 @@ _recv_raw_pkts_vec(struct i40e_rx_queue *rxq, struct rte_mbuf **rx_pkts,
 		_mm_storeu_si128((__m128i *)&rx_pkts[pos+2], mbp2);
 
 		if (split_packet) {
-			rte_prefetch0(&rx_pkts[pos]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 1]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 2]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 3]->cacheline1);
+			rte_mbuf_prefetch_part1(rx_pkts[pos]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 1]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 2]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 3]);
 		}
 
 		/*shift the pktlen field*/
diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
index 5040704..9bc7a5d 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
@@ -302,10 +302,10 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
 		_mm_storeu_si128((__m128i *)&rx_pkts[pos+2], mbp2);
 
 		if (split_packet) {
-			rte_prefetch0(&rx_pkts[pos]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 1]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 2]->cacheline1);
-			rte_prefetch0(&rx_pkts[pos + 3]->cacheline1);
+			rte_mbuf_prefetch_part1(rx_pkts[pos]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 1]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 2]);
+			rte_mbuf_prefetch_part1(rx_pkts[pos + 3]);
 		}
 
 		/* avoid compiler reorder optimization */
diff --git a/drivers/net/mlx4/mlx4.c b/drivers/net/mlx4/mlx4.c
index 4f21dbe..e7a426d 100644
--- a/drivers/net/mlx4/mlx4.c
+++ b/drivers/net/mlx4/mlx4.c
@@ -3235,8 +3235,8 @@ mlx4_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		 * Fetch initial bytes of packet descriptor into a
 		 * cacheline while allocating rep.
 		 */
-		rte_prefetch0(seg);
-		rte_prefetch0(&seg->cacheline1);
+		rte_mbuf_prefetch_part0(seg);
+		rte_mbuf_prefetch_part1(seg);
 		ret = rxq->if_cq->poll_length_flags(rxq->cq, NULL, NULL,
 						    &flags);
 		if (unlikely(ret < 0)) {
diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 9d1380a..3e901be 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1086,8 +1086,8 @@ mlx5_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		 * Fetch initial bytes of packet descriptor into a
 		 * cacheline while allocating rep.
 		 */
-		rte_prefetch0(seg);
-		rte_prefetch0(&seg->cacheline1);
+		rte_mbuf_prefetch_part0(seg);
+		rte_mbuf_prefetch_part1(seg);
 		ret = rxq->poll(rxq->cq, NULL, NULL, &flags, &vlan_tci);
 		if (unlikely(ret < 0)) {
 			struct ibv_wc wc;
diff --git a/examples/ipsec-secgw/ipsec-secgw.c b/examples/ipsec-secgw/ipsec-secgw.c
index 00ab2d8..ecaa197 100644
--- a/examples/ipsec-secgw/ipsec-secgw.c
+++ b/examples/ipsec-secgw/ipsec-secgw.c
@@ -298,7 +298,7 @@ prepare_tx_burst(struct rte_mbuf *pkts[], uint16_t nb_pkts, uint8_t port)
 	const int32_t prefetch_offset = 2;
 
 	for (i = 0; i < (nb_pkts - prefetch_offset); i++) {
-		rte_prefetch0(pkts[i + prefetch_offset]->cacheline1);
+		rte_mbuf_prefetch_part1(pkts[i + prefetch_offset]);
 		prepare_tx_pkt(pkts[i], port);
 	}
 	/* Process left packets */
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 529debb..e3ee0b3 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -842,6 +842,44 @@ struct rte_mbuf {
 	uint16_t timesync;
 } __rte_cache_aligned;
 
+/**
+ * Prefetch the first part of the mbuf
+ *
+ * The first 64 bytes of the mbuf corresponds to fields that are used early
+ * in the receive path. If the cache line of the architecture is higher than
+ * 64B, the second part will also be prefetched.
+ *
+ * @param m
+ *   The pointer to the mbuf.
+ */
+static inline void
+rte_mbuf_prefetch_part0(struct rte_mbuf *m)
+{
+	rte_prefetch0(&m->cacheline0);
+}
+
+/**
+ * Prefetch the second part of the mbuf
+ *
+ * The next 64 bytes of the mbuf corresponds to fields that are used in the
+ * transmit path. If the cache line of the architecture is higher than 64B,
+ * this function does nothing as it is expected that the full mbuf is
+ * already in cache.
+ *
+ * @param m
+ *   The pointer to the mbuf.
+ */
+static inline void
+rte_mbuf_prefetch_part1(struct rte_mbuf *m)
+{
+#if RTE_CACHE_LINE_SIZE == 64
+	rte_prefetch0(&m->cacheline1);
+#else
+	RTE_SET_USED(m);
+#endif
+}
+
+
 static inline uint16_t rte_pktmbuf_priv_size(struct rte_mempool *mp);
 
 /**
-- 
2.8.0.rc3