Commit 8eb77cc7 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jakub Kicinski
Browse files

ipv4: avoid partial copy for zc 



Even when zerocopy transmission is requested and possible,
__ip_append_data() will still copy a small chunk of data just because it
allocated some extra linear space (e.g. 148 bytes). It wastes CPU cycles
on copy and iter manipulations and also misalignes potentially aligned
data. Avoid such copies. And as a bonus we can allocate smaller skb.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 32346491

net/ipv4/ip_output.c

+6 −2
Original line number Diff line number Diff line
@@ -969,7 +969,6 @@ static int __ip_append_data(struct sock *sk, 
	struct inet_sock *inet = inet_sk(sk);

	struct ubuf_info *uarg = NULL;

	struct sk_buff *skb;



	struct ip_options *opt = cork->opt;

	int hh_len;

	int exthdrlen;
@@ -977,6 +976,7 @@ static int __ip_append_data(struct sock *sk, 
	int copy;

	int err;

	int offset = 0;

	bool zc = false;

	unsigned int maxfraglen, fragheaderlen, maxnonfragsize;

	int csummode = CHECKSUM_NONE;

	struct rtable *rt = (struct rtable *)cork->dst;
@@ -1025,6 +1025,7 @@ static int __ip_append_data(struct sock *sk, 
		if (rt->dst.dev->features & NETIF_F_SG &&

		    csummode == CHECKSUM_PARTIAL) {

			paged = true;

			zc = true;

		} else {

			uarg->zerocopy = 0;

			skb_zcopy_set(skb, uarg, &extra_uref);
@@ -1091,9 +1092,12 @@ static int __ip_append_data(struct sock *sk, 
				 (fraglen + alloc_extra < SKB_MAX_ALLOC ||

				  !(rt->dst.dev->features & NETIF_F_SG)))

				alloclen = fraglen;

			else {

			else if (!zc) {

				alloclen = min_t(int, fraglen, MAX_HEADER);

				pagedlen = fraglen - alloclen;

			} else {

				alloclen = fragheaderlen + transhdrlen;

				pagedlen = datalen - transhdrlen;

			}



			alloclen += alloc_extra;