https://bugs.freedesktop.org/show_bug.cgi?id=98239
--- Comment #3 from Marek Olšák maraeo@gmail.com --- Things to try:
1) You can try increasing the IB size in radeon_drm_cs.h: struct radeon_cs_context { uint32_t buf[16 * 1024]; // HERE
2) Add buffer-wait-time to the HUD and see if it corresponds with the flushes.