netdev - [PATCH net-next v3 0/3] net: tunnel: introduce noref xmit flows for tunnels

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Message-ID: <20250922110622.10368-1-mmietus97@yahoo.com>
Date: Mon, 22 Sep 2025 13:06:19 +0200
From: Marek Mietus <mmietus97@...oo.com>
To: netdev@...r.kernel.org,
	sd@...asysnail.net,
	antonio@...nvpn.net
Cc: openvpn-devel@...ts.sourceforge.net
Subject: [PATCH net-next v3 0/3] net: tunnel: introduce noref xmit flows for tunnels

Currently, all xmit flows use dst_cache in a way that references
its dst_entry for each xmitted packet. These atomic operations
are redundant in some flows.

This patchset introduces new noref xmit helpers and incorporates
them in the OpenVPN driver. A similar improvement can also be
applied to other tunnel code in the future. The implementation
for OpenVPN is a good starting point as it doesn't use the
udp_tunnel_dst_lookup helper which adds some complexity.

There are already noref optimizations in both ipv4 and ip6 
(See __ip_queue_xmit, inet6_csk_xmit). This patchset allows for
similar optimizations in udp tunnels. Referencing the dst_entry
is now redundant, as the entire flow is protected under RCU, so
it is removed.

With this patchset, I was able to observe a 4% decrease in the total
time for ovpn_udp_send_skb using perf.

Changes in v3:
 - Added implementation for ip6
 - Updated cover letter and commit messages

Link to v2: https://lore.kernel.org/netdev/20250912112420.4394-1-mmietus97@yahoo.com/
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2.51.0