udp: avoid one cache line miss in recvmsg()

UDP_SKB_CB(skb)->partial_cov is located at offset 66 in skb,
requesting a cold cache line being read in cpu cache.

We can avoid this cache line miss for UDP sockets,
as partial_cov has a meaning only for UDPLite.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -1389,7 +1389,8 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 	 * coverage checksum (UDP-Lite), do it before the copy.
 	 */
 
-	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov || peeking) {
+	if (copied < ulen || peeking ||
+	    (is_udplite && UDP_SKB_CB(skb)->partial_cov)) {
 		checksum_valid = !udp_lib_checksum_complete(skb);
 		if (!checksum_valid)
 			goto csum_copy_err;

net/ipv6/udp.c

@@ -363,7 +363,8 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	 * coverage checksum (UDP-Lite), do it before the copy.
 	 */
 
-	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov || peeking) {
+	if (copied < ulen || peeking ||
+	    (is_udplite && UDP_SKB_CB(skb)->partial_cov)) {
 		checksum_valid = !udp_lib_checksum_complete(skb);
 		if (!checksum_valid)
 			goto csum_copy_err;