To group and place certain instances or design elements as closely as possible, you can use the USER_CLUSTER property to specify the placement of grouped cells. This allows you to manage logic partitioning as well as the behavior of the Vivado Design Suite placer. You can specify the USER_CLUSTER property on a set of hierarchical instances to form a soft cluster that is taken into account during the SLR partitioning and partition-driven placer phases. For more information on this property, see the Vivado Design Suite Properties Reference Guide (UG912).
After you analyze the design, find the specific instances involved in the top failing paths, and determine whether the logic placement within the failing instance is spread out, you can use the USER_CLUSTER property to improve placement, which results in better performance of the design. In the following figure, the example on the left shows the default placement of the instance. The example on the right shows the placement of the instance after applying the USER_CLUSTER property.