I have Mikrotik Routerboard ccr1036-8g-2s+em with 1500 online pppoe users with avg overall traffic of 1.5 - 1.8 Gb (no natting, conn track turned off) with Firmware 6.44.6. User traffic is controlled by dynamically simple queue via radius. We are also marking packets going to CDN server via mangle and have created PCQ base simple queue (moved to top) to allow more bandwidth for CDN and dynamic queue take care of normal internet traffic. example 1mb for internet & 2mb for CDN traffic.
This part is working fine. but CDN traffic is putting high load on the CPU. as soon as I disable the CDN queues, things gets back to acceptable normal range.

I am trying to minimize CPU load by moving CDN pcq base simple queue to QUEUE TREE section but problem is that queue tree doesnt take priority for cdn. user traffic is still capped by the dynamic simple queue.

What method mikrotik base ISP's are using to achieve this sort of task? is simple queue better or queue tree?