A method of video processing is described. The method includes determining, for subblocks of a current video block of a video, subblock boundaries to which a deblocking filter is to be applied according to a rule; and performing a conversion between the video and a coded representation of the video using the deblocking filter, wherein the rule specifies that a deblocking filter length is determined without checking a relationship between i) a sum of a position of a subblock of the current video block and a predefined value and ii) a width or a height of the current video block.