svn commit: r312165 - stable/10/sys/dev/sfxge

[Andrew Rybchenko]

Author: arybchik
Date: Sat Jan 14 10:39:00 2017
New Revision: 312165
URL: https://svnweb.freebsd.org/changeset/base/312165

Log:
  MFC r311877
  
  sfxge(4): avoid unnecessary mbuf data prefetch
  
  Unnecessary prefetch just loads HW prefetcher and displaces other
  cache entries (which could be really useful).
  
  If we parse mbuf for TSO early and use firmware-assisted TSO, we do not
  expect mbuf data access when we compose firmware-assisted TSO (v1 or v2)
  option descriptors.  If packet header needs to be linearized or finally
  FATSO cannot be used because of, for example, too big header, we do not
  care about a bit more performance degradation because of prefetch
  absence (it is better to optimize more common case).
  
  Sponsored by:   Solarflare Communications, Inc.

Modified:
  stable/10/sys/dev/sfxge/sfxge_tx.c
Directory Properties:
  stable/10/   (props changed)

Modified: stable/10/sys/dev/sfxge/sfxge_tx.c
==============================================================================
--- stable/10/sys/dev/sfxge/sfxge_tx.c	Sat Jan 14 10:38:39 2017	(r312164)
+++ stable/10/sys/dev/sfxge/sfxge_tx.c	Sat Jan 14 10:39:00 2017	(r312165)
@@ -356,8 +356,22 @@ static int sfxge_tx_queue_mbuf(struct sf
 
 	KASSERT(!txq->blocked, ("txq->blocked"));
 
+#if SFXGE_TX_PARSE_EARLY
+	/*
+	 * If software TSO is used, we still need to copy packet header,
+	 * even if we have already parsed it early before enqueue.
+	 */
+	if ((mbuf->m_pkthdr.csum_flags & CSUM_TSO) &&
+	    (txq->tso_fw_assisted == 0))
+		prefetch_read_many(mbuf->m_data);
+#else
+	/*
+	 * Prefetch packet header since we need to parse it and extract
+	 * IP ID, TCP sequence number and flags.
+	 */
 	if (mbuf->m_pkthdr.csum_flags & CSUM_TSO)
 		prefetch_read_many(mbuf->m_data);
+#endif
 
 	if (__predict_false(txq->init_state != SFXGE_TXQ_STARTED)) {
 		rc = EINTR;