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ipv4: avoid partial copy for zc

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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: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Pavel Begunkov 2022-07-12 21:52:25 +01:00 committed by Jakub Kicinski
parent 32346491dd
commit 8eb77cc739
1 changed files with 6 additions and 2 deletions
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8
net/ipv4/ip_output.c
View file

@ -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;