igb: defeature tx head writeback

This patch removes tx head writeback as it was found to not provide a
significant improvement in tx performance and on some systems has been seen
to cause a performance degredation due to partial cache line writes.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/net/igb/e1000_defines.h b/drivers/net/igb/e1000_defines.h
index c5fe784c9e37..40d03426c122 100644
--- a/drivers/net/igb/e1000_defines.h
+++ b/drivers/net/igb/e1000_defines.h
@@ -323,6 +323,7 @@
 #define E1000_TXD_CMD_IFCS   0x02000000 /* Insert FCS (Ethernet CRC) */
 #define E1000_TXD_CMD_RS     0x08000000 /* Report Status */
 #define E1000_TXD_CMD_DEXT   0x20000000 /* Descriptor extension (0 = legacy) */
+#define E1000_TXD_STAT_DD    0x00000001 /* Descriptor Done */
 /* Extended desc bits for Linksec and timesync */
 
 /* Transmit Control */