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udp: add drop_counters to udp socket

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When a packet flood hits one or more UDP sockets, many cpus
have to update sk->sk_drops.

This slows down other cpus, because currently
sk_drops is in sock_write_rx group.

Add a socket_drop_counters structure to udp sockets.

Using dedicated cache lines to hold drop counters
makes sure that consumers no longer suffer from
false sharing if/when producers only change sk->sk_drops.

This adds 128 bytes per UDP socket.

Tested with the following stress test, sending about 11 Mpps
to a dual socket AMD EPYC 7B13 64-Core.

super_netperf 20 -t UDP_STREAM -H DUT -l10 -- -n -P,1000 -m 120
Note: due to socket lookup, only one UDP socket is receiving
packets on DUT.

Then measure receiver (DUT) behavior. We can see both
consumer and BH handlers can process more packets per second.

Before:

nstat -n ; sleep 1 ; nstat | grep Udp
Udp6InDatagrams                 615091             0.0
Udp6InErrors                    3904277            0.0
Udp6RcvbufErrors                3904277            0.0

After:

nstat -n ; sleep 1 ; nstat | grep Udp
Udp6InDatagrams                 816281             0.0
Udp6InErrors                    7497093            0.0
Udp6RcvbufErrors                7497093            0.0

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250826125031.1578842-5-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2025-08-26 12:50:30 +00:00 committed by Paolo Abeni
parent c51613fa27
commit 51132b99f0
4 changed files with 6 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/udp.h
View File

@ -108,6 +108,7 @@ struct udp_sock {
* the last UDP socket cacheline.
*/
struct hlist_node tunnel_list;
struct socket_drop_counters drop_counters;
};
#define udp_test_bit(nr, sk) \

1
include/net/udp.h
View File

@ -288,6 +288,7 @@ static inline void udp_lib_init_sock(struct sock *sk)
{
struct udp_sock *up = udp_sk(sk);
sk->sk_drop_counters = &up->drop_counters;
skb_queue_head_init(&up->reader_queue);
INIT_HLIST_NODE(&up->tunnel_list);
up->forward_threshold = sk->sk_rcvbuf >> 2;

3
tools/testing/selftests/bpf/progs/bpf_iter_udp4.c
View File

@ -64,7 +64,8 @@ int dump_udp4(struct bpf_iter__udp *ctx)
0, 0L, 0, ctx->uid, 0,
sock_i_ino(&inet->sk),
inet->sk.sk_refcnt.refs.counter, udp_sk,
inet->sk.sk_drops.counter);
udp_sk->drop_counters.drops0.counter +
udp_sk->drop_counters.drops1.counter);
return 0;
}

4
tools/testing/selftests/bpf/progs/bpf_iter_udp6.c
View File

@ -72,7 +72,7 @@ int dump_udp6(struct bpf_iter__udp *ctx)
0, 0L, 0, ctx->uid, 0,
sock_i_ino(&inet->sk),
inet->sk.sk_refcnt.refs.counter, udp_sk,
inet->sk.sk_drops.counter);
udp_sk->drop_counters.drops0.counter +
udp_sk->drop_counters.drops1.counter);
return 0;
}