/* To editors: https://forum.openwrt.org/t/dedicated-wiki-page-about-flow-offloading/224998 */
¶ Flow offloading
¶ Intro
The Flow offload may significantly increases throughput of device with slow CPU.
Some facts:
- Technically, the software flow offload is just a firewall rule.
- Neither flow forwarding offload is directly related to network adapter offload functions controlled by
ethtool -k/-K. - Flow offloading applies to forwarded connections, including those to containers like LXC or podman, but not locally running web-server.
- Hardware offload bypasses QoS traffic controls at high priority making former ineffective.
- Hardware offload can handle very limited number of connections at once, e.g. 64, thus will not significantly help p2p, returning surplus connections to software offload pool.
- Software offload typically increases forwarding bandwidth 2-3x over firewall filtering each packet, sometimes that relieves fully loaded CPU and improves overall latency/jitter.
Abbreviations:
- <abbr title="Hardware flow offloading">HFO</abbr> — hardware flow offloading.
- <abbr title="Wireless Ethernet dispatch">WED</abbr> — wireless offloading, wireless Ethernet dispatch.
- <abbr title="Packet processing engine">PPE</abbr> — kernel interface for hardware flow offload, monitored via
/sys/kernel/debug/ppe0/entriesspecial file.
¶ How to enable
¶ LuCI web UI
Using LuCI web UI: Network -> Firewall and select "Software flow offloading" or "Hardware flow offloading", then hit "Save & Apply".
¶ UCI
CLI with UCI (choose the one option you want):
uci set 'firewall.@defaults[0].flow_offloading=1'
uci set 'firewall.@defaults[0].flow_offloading_hw=1'
uci commit
/etc/init.d/firewall restart
¶ CLI
CLI: edit /etc/config/firewall and insert the following under the config defaults section (choose the one option you want):
config defaults
…
option flow_offloading '1'
option flow_offloading_hw '1'
Then restart the firewall:
/etc/init.d/firewall restart
¶ Hardware implementation
¶ MediaTek mt76
The main page about MediaTek chipsets: soc.mediatek.
Hardware offloading is supported on mt76 platforms starting from SoC mt7621.
WED enablement (i.e hardware offloading for Wi-Fi): TODO.
¶ Known issues
- The Hardware offload is supported by limited amount of platforms.
- Stale connections/freezes when changing Wi-Fi band (for example from 2.4 GHz to 5 GHz).
- Prevents Wi-Fi roaming by keeping stale connection mappings.
¶ Links
- Netfilter’s flowtable infrastructure — the Linux kernel documentation with description of both Software flow offload and Hardware offload and with a list of limitations.