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Hermes SMTP Server) with ESMTPA ID 5c743ac7fc5feeb5bdbb197ea32f25e9; Tue, 20 Jan 2026 16:27:41 +0000 (UTC) From: Marek Mietus To: netdev@vger.kernel.org, sd@queasysnail.net, kuba@kernel.org Cc: Jason@zx2c4.com, Marek Mietus Subject: [PATCH net-next v6 08/11] net: tunnel: convert ip_tunnel_xmit to use a noref dst when possible Date: Tue, 20 Jan 2026 17:24:48 +0100 Message-ID: <20260120162451.23512-9-mmietus97@yahoo.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260120162451.23512-1-mmietus97@yahoo.com> References: <20260120162451.23512-1-mmietus97@yahoo.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ip_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_tunnel_xmit. Signed-off-by: Marek Mietus --- net/ipv4/ip_tunnel.c | 31 +++++++++++++++++++------------ 1 file changed, 19 insertions(+), 12 deletions(-) diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 40ff6ad9b9b9..146e354810d2 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -681,6 +681,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, struct rtable *rt = NULL; /* Route to the other host */ __be16 payload_protocol; bool use_cache = false; + bool noref = true; struct flowi4 fl4; bool md = false; bool connected; @@ -775,11 +776,11 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (connected && md) { 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); } else { - rt = connected ? dst_cache_get_ip4(&tunnel->dst_cache, - &fl4.saddr) : NULL; + rt = connected ? dst_cache_get_ip4_rcu(&tunnel->dst_cache, + &fl4.saddr) : NULL; } if (!rt) { @@ -790,15 +791,18 @@ void ip_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); else if (!md && connected) - dst_cache_set_ip4(&tunnel->dst_cache, &rt->dst, - fl4.saddr); + dst_cache_steal_ip4(&tunnel->dst_cache, &rt->dst, + fl4.saddr); + else + noref = false; } if (rt->dst.dev == dev) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); DEV_STATS_INC(dev, collisions); goto tx_error; } @@ -808,7 +812,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, df |= (inner_iph->frag_off & htons(IP_DF)); if (tnl_update_pmtu(dev, skb, rt, df, inner_iph, 0, 0, false)) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); goto tx_error; } @@ -839,7 +844,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, + rt->dst.header_len + ip_encap_hlen(&tunnel->encap); if (skb_cow_head(skb, max_headroom)) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); DEV_STATS_INC(dev, tx_dropped); kfree_skb(skb); return; @@ -849,7 +855,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, protocol, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev)), 0); - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); return; #if IS_ENABLED(CONFIG_IPV6) -- 2.51.0