netdev - [PATCH net-next] udp: avoid one cache line miss in recvmsg()

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Date:   Fri, 18 Nov 2016 17:18:03 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] udp: avoid one cache line miss in recvmsg()

From: Eric Dumazet <edumazet@...gle.com>

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: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/udp.c |    3 ++-
 net/ipv6/udp.c |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e1fc0116e8d59d8185670c6e55d1219bde55610d..b949770fdc08398a10f3974505a50b2b4f4b2cf3 100644
--- a/net/ipv4/udp.c
+++ b/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;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 4f99417d9b401f2a65c7828e7d6b86d1d6161794..8fd4d89380b86c8630f7fd27ce4e9958497a2b89 100644
--- a/net/ipv6/udp.c
+++ b/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;