2D defragmentation heuristics for hardware multitasking on reconfigurable devices

This paper focuses on the fragmentation problem produced in 2D run-time reconfigurable FPGAs when hardware multitasking management is considered. Though allocation heuristics can take fragmentation into account when a new task arrives, the free area becomes inevitably fragmented as the tasks finish and exit the FPGA. The main contributions of our work are a fragmentation metric able to estimate when the FPGA fragmentation status has become critical, and several heuristics to decide when to perform defragmentation and how to perform it. This defragmentation heuristics can be of a preventive kind, driven by alarms that fire when isolated islands appear or a high fragmentation status is reached. It can be also an on-demand process produced when a task allocation fails though there is enough free area in the FPGA to accommodate it.