Comment # 3 on bug 97075 from Christoph Haag

I put the issue in DRM/radeon instead of mesa/radeonsi because I thought it
would be related to power management.

I tried
echo high > /sys/class/drm/card1/device/power_dpm_force_performance_level
and
performance > /sys/class/drm/card1/device/power_dpm_state
but it makes no difference, still just as slow.