[PATCH net-next v6 07/11] net: tunnel: convert ip_md_tunnel_xmit to use a noref dst when possible
From: Marek Mietus <hidden>
Date: 2026-01-20 16:37:39
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
ip_md_tunnel_xmit unnecessarily references the dst_entry from the dst_cache when interacting with the cache. Reduce this overhead by avoiding the redundant refcount increments. This is only possible in flows where the cache is used. Otherwise, we fall-back to a referenced dst. This change is safe since ipv4 supports noref xmit under RCU which is already the case for ip_md_tunnel_xmit. Signed-off-by: Marek Mietus <redacted> --- net/ipv4/ip_tunnel.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 2136a46bcdc5..40ff6ad9b9b9 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c@@ -609,7 +609,7 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, use_cache = ip_tunnel_dst_cache_usable(skb, tun_info); if (use_cache) - rt = dst_cache_get_ip4(&tun_info->dst_cache, &fl4.saddr); + rt = dst_cache_get_ip4_rcu(&tun_info->dst_cache, &fl4.saddr); if (!rt) { rt = ip_route_output_key(tunnel->net, &fl4); if (IS_ERR(rt)) {
@@ -617,11 +617,12 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, goto tx_error; } if (use_cache) - dst_cache_set_ip4(&tun_info->dst_cache, &rt->dst, - fl4.saddr); + dst_cache_steal_ip4(&tun_info->dst_cache, &rt->dst, + fl4.saddr); } if (rt->dst.dev == dev) { - ip_rt_put(rt); + if (!use_cache) + ip_rt_put(rt); DEV_STATS_INC(dev, collisions); goto tx_error; }
@@ -630,7 +631,8 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, df = htons(IP_DF); if (tnl_update_pmtu(dev, skb, rt, df, inner_iph, tunnel_hlen, key->u.ipv4.dst, true)) { - ip_rt_put(rt); + if (!use_cache) + ip_rt_put(rt); goto tx_error; }
@@ -647,7 +649,8 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, headroom += LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len; if (skb_cow_head(skb, headroom)) { - ip_rt_put(rt); + if (!use_cache) + ip_rt_put(rt); goto tx_dropped; }
@@ -655,7 +658,8 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, proto, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev)), 0); - ip_rt_put(rt); + if (!use_cache) + ip_rt_put(rt); return; tx_error: DEV_STATS_INC(dev, tx_errors);
--
2.51.0