I recently observed that a 225 Mbps downstream connection is limited to approx 150 Mbps if SQM/QoS is enabled due to the saturation of the router's CPU. Link. This is running 19.07.0-rc2 on a R7800 which is one of the most powerful CPUs supported by OpenWRT, dual core 1.70 GHz CPU. You can read through the linked thread for details but in summary the recommended SQM, cake/piece_of_cake.qos saturates the one of the CPUs which causes the limited speed.
I am wondering if there can be improvements to the SQM to optimize CPU usage and to allow for faster throughput. For example, an ISP is in my city advertising 1000 Mbps downstream. If I am tuning for bufferbloat, I would think the CPU bound nature would severely limit it. Thanks!