Recent evidence on perovskite to post-perovskite phase change in the lowermost mantle suggests that post-perovskite piles or lens should be present in the relatively cold downwelling areas, while the roots of the hot upwelling plumes consist of perovskite. Post-perovskite is often believed to be deformed predominantly by the dislocation creep and there are some hints that the activation parameters of the dislocation creep in post-perovskite induce lower viscosity than that of perovskite at the same pressure and temperature conditions.