I'm using a Redmi AC2100 for a while with Stock firmware (latest version). I already knew OpenWRT since 2011 but only now I decided to reinstall, but for some reason the bandwidth was reduced by up to 25%!!!! The contracted speed is 600Mbps, and normally with Stock it reaches that speed. I installed OpenWRT and only got around 100Mbps. Even without installing any router app. The only configuration I did was to disable IPv6 and change Wan to PPPoe. Something I did wrong?
I think so try to test speed between your router and your computer. Also try to check speed between your router and ISP provider. You can install speedtest on your router.
Neither of those tests is useful, especially on weaker SOCs. Common consumer router are optimized to route, not to be the endpoint of consuming or generating traffic. Accordingly a router tends to be considerably faster to pass traffic through (in the sense of routing), than to act as client or server.
mt7621a as a SOC isn't particularly fast (2*880 MHz mips 1004Kc), it relies upon (very-) well optimized networking drivers and packet processing engines for offloading. Having to do PPPoE would be a further complication, requiring considerably more processing power than mere (ethernet-) routing.
Enabling hardware flow-offloading should help you improve your routing performance (it's a mainline implementation roughly doing what the OEM firmware does as well), which should provide a significant speed up for the simple cases (PPPoE is a bit beyond simple, but it might still suffice), but if you're looking for advanced features as well (SQM/ QoS, VPN, etc.), this SOC is too slow for these WAN speeds.
If not tried already,
Give a Development Snapshot a try. Routers using the MediaTek MT7621AT with WiFi chip, frequently has bugs of one sort or another.
Try one of the Padavan builds, it’s a OpenWRT spin-off optimized for mt7621 with mtk’s driver, there are several well know maintainers on github, and they all pretty much surpass stock Opwrt’s opensource driver in wifi performance(sad but true).
There is also a YouTube vid with more detailed comparisons.
I actually did a very short search on the subject. everyone, thanks for the answer and I'll see what I can do about it to change the rotator, or even mount one of mine with my Rpi3b.
@Amitofo I didn't know this project fork. I will try to find out more.
Did you try to enable Packet Steering?