Comment # 2 on bug 79850 from Michel Dänzer

Are you sure it's using page flipping? If you write 2 to
/sys/module/drm/parameters/debug, do you get messages like

 [drm:radeon_crtc_page_flip] flip-ioctl() cur_fbo = ffff880100f89000, cur_bbo =
ffff88000d714800

in dmesg?