Does interface queue use CPU?

I am reading Edge Router & BNG Optimisation Guide for ISPs and implementing some of its advice. However, under QoS and Bufferbloat control, it says


This means configuration wise, you apply the FQ_Codel queueing to all your physical ports and wireless interfaces across all your network devices. And ensure for customer queueing the same queue type is used.

I have already done this to my core and aggregation routers. The issue is that my traffic passes through some switches. My core switch is a CRS326-24S+2Q+RM, and some traffic (around 1.5Gbit) passes through some CRS326-24G-2S+RM units.

They don’t have the best CPU.

Should I still apply the hardware queue advice for them? Or leave them on only-hardware-queue?

Does ECN still work if the devices between ECN-enabled devices don’t have ECN?