Unloading unused kernel modules (NAT speed)

[Florian Fainelli]

On 2/3/23 08:18, Rafał Miłecki wrote:
> Another step in my NAT performance debugging.
> 
> I realized that my OpenWrt 21.02 based bcm53xx builds can't reach 940
> Mb/s because I have qos-scripts installed.
> 
> It happens even with QoS interface disabled:
> qos.wan.enabled='0'
> and with QoS disabled in general:
> /etc/init.d/qos stop
> (disable & reboot don't help neither)
> 
> After quite some debugging I discovered that:
> 1. qos-scripts selects iptables-mod-conntrack-extra
> 2. iptables-mod-conntrack-extra selects kmod-ipt-raw
> 3. kmod-ipt-raw provides iptable_raw.ko
> 4. iptable_raw.ko slows down NAT
> 
> 
> I can bump NAT speed from 880 Mb/s to 940 Mb/s by doing:
> 
> # rmmod iptable_raw
> unloading the module failed
> # /etc/init.d/firewall stop > /dev/null 2>&1
> # rmmod iptable_raw
> # /etc/init.d/firewall start > /dev/null 2>&1
> 
> 
> I'm wondering if there is any good solution to that. I can't think of
> anything clean and generic. Handling modprobe & rmmod directly in
> /etc/init.d/qos sounds really hacky. Any good ideas?

Have you managed to get a `perf record` or `perf top` capture to see 
whether we might be going a little too far into iptables-raw code rather 
than bailing out early if we are not utilizing it?
-- 
Florian