[dpdk-dev] [PATCH] net/mlx5: remove excessive data prefetch

[Yongseok Koh <yskoh@mellanox.com>]

In Enhanced Multi-Packet Send (eMPW), entire packet data is prefetched to
LLC if it isn't inlined. Even though this helps reducing jitter when HW
fetches data by DMA, this can thresh the LLC with evicting precious data.
And if the size of queue is large and there are many queues, this might not
be effective. Also, if application runs on a remote node from the PCIe
link, it may not be helpful and can even cause bad results.

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
---
 drivers/net/mlx5/mlx5_rxtx.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 049f7e6c1..c2060b734 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1320,7 +1320,6 @@ txq_burst_empw(struct mlx5_txq_data *txq, struct rte_mbuf **pkts,
 	do {
 		struct rte_mbuf *buf = *(pkts++);
 		uintptr_t addr;
-		unsigned int n;
 		unsigned int do_inline = 0; /* Whether inline is possible. */
 		uint32_t length;
 		uint8_t cs_flags;
@@ -1440,11 +1439,8 @@ txq_burst_empw(struct mlx5_txq_data *txq, struct rte_mbuf **pkts,
 					((uintptr_t)mpw.data.raw +
 					 inl_pad);
 			(*txq->elts)[elts_head++ & elts_m] = buf;
-			addr = rte_pktmbuf_mtod(buf, uintptr_t);
-			for (n = 0; n * RTE_CACHE_LINE_SIZE < length; n++)
-				rte_prefetch2((void *)(addr +
-						n * RTE_CACHE_LINE_SIZE));
-			addr = rte_cpu_to_be_64(addr);
+			addr = rte_cpu_to_be_64(rte_pktmbuf_mtod(buf,
+								 uintptr_t));
 			*dseg = (rte_v128u32_t) {
 				rte_cpu_to_be_32(length),
 				mlx5_tx_mb2mr(txq, buf),
-- 
2.11.0