(In reply to Kai from comment #8)
> (In reply to Alex Deucher from comment #6)
> > Does reverting 5e031d9fe8b0741f11d49667dfc3ebf5454121fd (drm/radeon/pm:
> > update current crtc info after setting the powerstate) help?
> 
> No, it does not for me (I fetched the patch from
> <https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/patch/
> ?id=5e031d9fe8b0741f11d49667dfc3ebf5454121fd> and applied it with patch -p1
> -R < /path/to.patch). The Talos Principle is still down to 43 FPS, haven't
> tested XCOM 2 or anything else.
> 
> Btw, not sure if it can help tracking down the cause: the GPU doesn't seem
> to go into its highest performance mode or at least the fan is not reaching
> its highest RPM when I'm on 4.7.0 (with or without the revert).

You can check by running apps and monitoring the content of
/sys/kernel/debug/dri/64/radeon_pm_info
Do you see it scaling up under load on the problematic kernels?  Does forcing
the clocks to high via sysfs work ok?