From 《红楼梦》 chapter 53 (Cao Xueqin, Qing dynasty): "此时荣宁二府内外上下,皆是忙忙碌碌" — both Rong and Ning mansions, top to bottom, were in bustling motion (preparing for New Year).
grammar
AABB reduplication of 忙碌 (busy). The reduplicated form feels more vivid and continuous than plain 忙碌 — a whole day, a whole season of buzzing around.