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Commit d21dbdfe authored Nov 18, 2016 by Eric Dumazet Committed by David S. Miller Nov 21, 2016

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: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent ee9d5461

net/ipv4/udp.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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

+2 −1

Original line number	Diff line number	Diff line
		@@ -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;