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Hermes SMTP Server) with ESMTPA ID 8a3972250952fefb5c72bc783ca56e47; Wed, 12 Nov 2025 07:33:57 +0000 (UTC) From: Marek Mietus To: netdev@vger.kernel.org, sd@queasysnail.net, kuba@kernel.org Cc: Marek Mietus Subject: [PATCH net-next v4 11/14] net: tunnel: convert ip_tunnel_xmit to use a noref dst when possible Date: Wed, 12 Nov 2025 08:33:21 +0100 Message-ID: <20251112073324.5301-2-mmietus97@yahoo.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251112072720.5076-1-mmietus97@yahoo.com> References: <20251112072720.5076-1-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 | 38 +++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 323d085cc377..65f4e1cda69d 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -685,6 +685,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, bool use_cache = false; struct flowi4 fl4; bool md = false; + dstref_t dstref; bool connected; u8 tos, ttl; __be32 dst; @@ -777,30 +778,37 @@ 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) { + if (rt) { + dstref = dst_to_dstref_noref(&rt->dst); + } else { rt = ip_route_output_key(tunnel->net, &fl4); if (IS_ERR(rt)) { DEV_STATS_INC(dev, tx_carrier_errors); goto tx_error; } - if (use_cache) - dst_cache_set_ip4(&tun_info->dst_cache, &rt->dst, - fl4.saddr); - else if (!md && connected) - dst_cache_set_ip4(&tunnel->dst_cache, &rt->dst, - fl4.saddr); + if (use_cache) { + dst_cache_steal_ip4(&tun_info->dst_cache, &rt->dst, + fl4.saddr); + dstref = dst_to_dstref_noref(&rt->dst); + } else if (!md && connected) { + dst_cache_steal_ip4(&tunnel->dst_cache, &rt->dst, + fl4.saddr); + dstref = dst_to_dstref_noref(&rt->dst); + } else { + dstref = dst_to_dstref(&rt->dst); + } } if (rt->dst.dev == dev) { - ip_rt_put(rt); + dstref_drop(dstref); DEV_STATS_INC(dev, collisions); goto tx_error; } @@ -810,7 +818,7 @@ 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); + dstref_drop(dstref); goto tx_error; } @@ -841,7 +849,7 @@ 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); + dstref_drop(dstref); DEV_STATS_INC(dev, tx_dropped); kfree_skb(skb); return; @@ -849,7 +857,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, ip_tunnel_adj_headroom(dev, max_headroom); - iptunnel_xmit(NULL, dst_to_dstref(&rt->dst), skb, fl4.saddr, fl4.daddr, protocol, tos, ttl, + iptunnel_xmit(NULL, dstref, skb, fl4.saddr, fl4.daddr, protocol, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev)), 0); return; -- 2.51.0