igb: drop support for UDP hashing w/ RSS

This change removes UDP from the supported protocols for RSS hashing.  The
reason for removing this protocol is because IP fragmentation was causing a
network flow to be broken into two streams, one for fragmented, and one for
non-fragmented and this in turn was causing out-of-order issues.
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>

drivers/net/igb/igb_main.c

@@ -2717,14 +2717,16 @@ static void igb_setup_mrqc(struct igb_adapter *adapter)
 	}
 	igb_vmm_control(adapter);
 
-	mrqc |= (E1000_MRQC_RSS_FIELD_IPV4 |
-		 E1000_MRQC_RSS_FIELD_IPV4_TCP);
-	mrqc |= (E1000_MRQC_RSS_FIELD_IPV6 |
-		 E1000_MRQC_RSS_FIELD_IPV6_TCP);
-	mrqc |= (E1000_MRQC_RSS_FIELD_IPV4_UDP |
-		 E1000_MRQC_RSS_FIELD_IPV6_UDP);
-	mrqc |= (E1000_MRQC_RSS_FIELD_IPV6_UDP_EX |
-		 E1000_MRQC_RSS_FIELD_IPV6_TCP_EX);
+	/*
+	 * Generate RSS hash based on TCP port numbers and/or
+	 * IPv4/v6 src and dst addresses since UDP cannot be
+	 * hashed reliably due to IP fragmentation
+	 */
+	mrqc |= E1000_MRQC_RSS_FIELD_IPV4 |
+		E1000_MRQC_RSS_FIELD_IPV4_TCP |
+		E1000_MRQC_RSS_FIELD_IPV6 |
+		E1000_MRQC_RSS_FIELD_IPV6_TCP |
+		E1000_MRQC_RSS_FIELD_IPV6_TCP_EX;
 
 	wr32(E1000_MRQC, mrqc);
 }