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net: use NUMA drop counters for softnet_data.dropped

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Hosts under DOS attack can suffer from false sharing
in enqueue_to_backlog() : atomic_inc(&sd->dropped).

This is because sd->dropped can be touched from many cpus,
possibly residing on different NUMA nodes.

Generalize the sk_drop_counters infrastucture
added in commit c51613fa27 ("net: add sk->sk_drop_counters")
and use it to replace softnet_data.dropped
with NUMA friendly softnet_data.drop_counters.

This adds 64 bytes per cpu, maybe more in the future
if we increase the number of counters (currently 2)
per 'struct numa_drop_counters'.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250909121942.1202585-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2025-09-09 12:19:42 +00:00
committed by Jakub Kicinski
parent 278289bcec
commit fdae0ab67d
7 changed files with 45 additions and 31 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
include/net/sock.h
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@@ -102,11 +102,6 @@ struct net;
typedef __u32 __bitwise __portpair;
typedef __u64 __bitwise __addrpair;
struct socket_drop_counters {
atomic_t drops0 ____cacheline_aligned_in_smp;
atomic_t drops1 ____cacheline_aligned_in_smp;
};
/**
* struct sock_common - minimal network layer representation of sockets
* @skc_daddr: Foreign IPv4 addr
@@ -287,7 +282,7 @@ struct sk_filter;
* @sk_err_soft: errors that don't cause failure but are the cause of a
* persistent failure not just 'timed out'
* @sk_drops: raw/udp drops counter
* @sk_drop_counters: optional pointer to socket_drop_counters
* @sk_drop_counters: optional pointer to numa_drop_counters
* @sk_ack_backlog: current listen backlog
* @sk_max_ack_backlog: listen backlog set in listen()
* @sk_uid: user id of owner
@@ -456,7 +451,7 @@ struct sock {
#ifdef CONFIG_XFRM
struct xfrm_policy __rcu *sk_policy[2];
#endif
struct socket_drop_counters *sk_drop_counters;
struct numa_drop_counters *sk_drop_counters;
__cacheline_group_end(sock_read_rxtx);
__cacheline_group_begin(sock_write_rxtx);
@@ -2698,18 +2693,12 @@ struct sock_skb_cb {
static inline void sk_drops_add(struct sock *sk, int segs)
{
struct socket_drop_counters *sdc = sk->sk_drop_counters;
struct numa_drop_counters *ndc = sk->sk_drop_counters;
if (sdc) {
int n = numa_node_id() % 2;
if (n)
atomic_add(segs, &sdc->drops1);
else
atomic_add(segs, &sdc->drops0);
} else {
if (ndc)
numa_drop_add(ndc, segs);
else
atomic_add(segs, &sk->sk_drops);
}
}
static inline void sk_drops_inc(struct sock *sk)
@@ -2719,23 +2708,21 @@ static inline void sk_drops_inc(struct sock *sk)
static inline int sk_drops_read(const struct sock *sk)
{
const struct socket_drop_counters *sdc = sk->sk_drop_counters;
const struct numa_drop_counters *ndc = sk->sk_drop_counters;
if (sdc) {
if (ndc) {
DEBUG_NET_WARN_ON_ONCE(atomic_read(&sk->sk_drops));
return atomic_read(&sdc->drops0) + atomic_read(&sdc->drops1);
return numa_drop_read(ndc);
}
return atomic_read(&sk->sk_drops);
}
static inline void sk_drops_reset(struct sock *sk)
{
struct socket_drop_counters *sdc = sk->sk_drop_counters;
struct numa_drop_counters *ndc = sk->sk_drop_counters;
if (sdc) {
atomic_set(&sdc->drops0, 0);
atomic_set(&sdc->drops1, 0);
}
if (ndc)
numa_drop_reset(ndc);
atomic_set(&sk->sk_drops, 0);
}