https://bugs.freedesktop.org/show_bug.cgi?id=79850
--- Comment #2 from Michel Dänzer michel@daenzer.net --- 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?