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udp: add local "peek offset enabled" flag 

We want to re-organize the struct sock layout. The sk_peek_off
field location is problematic, as most protocols want it in the
RX read area, while UDP wants it on a cacheline different from
sk_receive_queue.

Create a local (inside udp_sock) copy of the 'peek offset is enabled'
flag and place it inside the same cacheline of reader_queue.

Check such flag before reading sk_peek_off. This will save potential
false sharing and cache misses in the fast-path.

Tested under UDP flood with small packets. The struct sock layout
update causes a 4% performance drop, and this patch restores completely
the original tput.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/67ab679c15fbf49fa05b3ffe05d91c47ab84f147.1708426665.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2024-02-20 12:00:01 +01:00 committed by Jakub Kicinski
parent 26b2a265d8
commit f796feabb9
4 changed files with 13 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/udp.h
View File

@ -92,6 +92,9 @@ struct udp_sock {
/* This fields follows rcvbuf value, and is touched by udp_recvmsg */
int forward_threshold;
/* Cache friendly copy of sk->sk_peek_off >= 0 */
bool peeking_with_offset;
};
#define udp_test_bit(nr, sk) \
@ -109,6 +112,13 @@ struct udp_sock {
#define udp_sk(ptr) container_of_const(ptr, struct udp_sock, inet.sk)
static inline int udp_set_peek_off(struct sock *sk, int val)
{
sk_set_peek_off(sk, val);
WRITE_ONCE(udp_sk(sk)->peeking_with_offset, val >= 0);
return 0;
}
static inline void udp_set_no_check6_tx(struct sock *sk, bool val)
{
udp_assign_bit(NO_CHECK6_TX, sk, val);

2
net/ipv4/af_inet.c
View File

@ -1103,7 +1103,7 @@ const struct proto_ops inet_dgram_ops = {
.recvmsg = inet_recvmsg,
.mmap = sock_no_mmap,
.splice_eof = inet_splice_eof,
.set_peek_off = sk_set_peek_off,
.set_peek_off = udp_set_peek_off,
#ifdef CONFIG_COMPAT
.compat_ioctl = inet_compat_ioctl,
#endif

2
net/ipv4/udp.c
View File

@ -1589,7 +1589,7 @@ int udp_init_sock(struct sock *sk)
void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
{
if (unlikely(READ_ONCE(sk->sk_peek_off) >= 0)) {
if (unlikely(READ_ONCE(udp_sk(sk)->peeking_with_offset))) {
bool slow = lock_sock_fast(sk);
sk_peek_offset_bwd(sk, len);

2
net/ipv6/af_inet6.c
View File

@ -736,7 +736,7 @@ const struct proto_ops inet6_dgram_ops = {
.recvmsg = inet6_recvmsg, /* retpoline's sake */
.read_skb = udp_read_skb,
.mmap = sock_no_mmap,
.set_peek_off = sk_set_peek_off,
.set_peek_off = udp_set_peek_off,
#ifdef CONFIG_COMPAT
.compat_ioctl = inet6_compat_ioctl,
#endif