The Spectre mitigations are supposed to cause a small CPU performance hit (somewhere along the lines of 5-10%). And for most processors, that is what I have observed. But for certain AMD APUs, the hit has been much larger—in the 500-1,000% range.
So far, I have only observed these symptoms on AMD A6-9220 and A10-9600P APUs. I don’t see these symptoms in other AMD APUs, like the A8-3250M, A9-9420, or the Ryzen 5 2500U (they don’t call it an APU anymore, but it is still an integrated CPU and GPU).
The symptoms are as follows: every activity is heavily CPU intensive. Just moving the mouse rapidly using the trackpad can pump the Synaptic driver CPU usage to 35%. Loading a standard website with any browser can take 60-120 seconds with the CPU pegged at 100% the entire time.
Disabling the Spectre V2 mitigations using the two registry keys described in the website below restores performance to expected levels.
Hopefully this is something that Microsoft fixes in the near future. They have already revised their Spectre patches several times. But I’m not holding my breath.