Piece_of_cake.qos cuts d/l speed by 2?

I am running OpenWrt 22.03.2 on a Linksys WRT3200ACM.

With SQM QOS disabled, I see about 720 Mbps download speed as measured with Ookla Speedtest. With piece_of_cake.qos enabled, and download speed set to 684000 (95% of 720 Mbps), Speedtest only measures about 320 Mbps. Is that expected? I am the only one using network resources.

This device does not have a powerful enough CPU to be able to shape with SQM at 720Mbps.

It's CPU-bound. You need more powerful hardware.

Suggest only enabling it on upload.

Also suggest reading this thread:So you have 500Mbps-1Gbps fiber and need a router READ THIS FIRST

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To illustrate just how much CPU SQM uses, this is htop showing resource usage with SQM enabled on download (on the top) and disabled (on the bottom).

For perspective, this is an 8-core x86_64. So a 2-core Marvel Armada is going to struggle for sure.

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On my turris omnia, the best I could get it to shape reliably was 550/550 Mbps, for bi directionally saturating traffic with MTU 1500, unidirectional traffic might reach a bit higher but it depends on what else runs on the router...

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Thanks for the replies. I'll look into getting a new router.