svn commit: r341552 - head/sys/dev/mlx4/mlx4_en

[Slava Shwartsman]

Author: slavash
Date: Wed Dec  5 13:39:35 2018
New Revision: 341552
URL: https://svnweb.freebsd.org/changeset/base/341552

Log:
  mlx4en: Optimise reception of small packets.
  
  Copy small packets like TCP ACKs into a new mbuf
  reusing the existing mbuf to receive a new ethernet
  frame. This avoids wasting buffer space for
  small sized packets.
  
  Submitted by:   hselasky@
  Approved by:    hselasky (mentor)
  MFC after:      1 week
  Sponsored by:   Mellanox Technologies

Modified:
  head/sys/dev/mlx4/mlx4_en/mlx4_en_rx.c

Modified: head/sys/dev/mlx4/mlx4_en/mlx4_en_rx.c
==============================================================================
--- head/sys/dev/mlx4/mlx4_en/mlx4_en_rx.c	Wed Dec  5 13:39:05 2018	(r341551)
+++ head/sys/dev/mlx4/mlx4_en/mlx4_en_rx.c	Wed Dec  5 13:39:35 2018	(r341552)
@@ -629,6 +629,24 @@ mlx4_en_rx_mb(struct mlx4_en_priv *priv, struct mlx4_e
 #endif
 	struct mbuf *mb;
 
+	/* optimise reception of small packets */
+	if (length <= (MHLEN - MLX4_NET_IP_ALIGN) &&
+	    (mb = m_gethdr(M_NOWAIT, MT_DATA)) != NULL) {
+
+		/* set packet length */
+		mb->m_pkthdr.len = mb->m_len = length;
+
+		/* make sure IP header gets aligned */
+		mb->m_data += MLX4_NET_IP_ALIGN;
+
+		bus_dmamap_sync(ring->dma_tag, mb_list->dma_map,
+		    BUS_DMASYNC_POSTREAD);
+
+		bcopy(mtod(mb_list->mbuf, caddr_t), mtod(mb, caddr_t), length);
+
+		return (mb);
+	}
+
 	/* get mbuf */
 	mb = mb_list->mbuf;