If you consistently encounter 100% CPU utilization even during periods of normal network activity,
it can only mean two things.

1. Badly-coded firmware
2. Failing or defective hardware.

The Broadcom BCM47189 @ 900 MHz in the Archer C1200 is quite a respectable processor.

It would be very difficult to max it out even under very heavy loads.

Instantaneous 100% peaks are possible, but not consistently at 100%.

Yeah, the culprit is most probably badly coded firmware.

The TP-Link Archer C1200 was only released in Feb 2017.

It is too new to be supported by DD-WRT.

Here is the list of TP-Link supported devices.

http://www.dd-wrt.com/wiki/index.php/Suppo...Devices#TP-Link

Is he talking about the C1200?

I am confused.

This confirms that the issue is with TP-Link's badly-coded firmware.

For comparison, here is a snapshot of my Huawei WS880 dual-core 800MHz Broadcom processor running Xwrt-Vortex firmware.

There are currently 7 devices connected to the router.

One with LAN cable, three on 2.4GHz and three on 5GHz.

Two of them are torrenting and one is streaming 1080p60fps video, the rest are surfing the web.

The total dual-core processor utilization is only a total of 10%, hardly breaking a sweat.

No wonder the new TP-Link Archer C1200 is not on the DD-WRT support list.