SPY vs. SLY: Run-time thread-scheduler aware reconfigurable hardware allocators

Periodic run-time scheduling of reconfigurable hardware (RH) is based on a simple prediction: RH needs in the near future will be similar to that of the recent past. Generally, this prediction is good; application behavior is phased, and RH needs are stable in each phase. A short RH scheduling interval then allows the system to adapt to application phase changes. However, there is one important case in multitasking systems where recent past behavior does not predict the near future: application thread context switch. When the OS performs a context switch, a different application will execute and have different RH needs. In this paper, we present two run-time thread-scheduler aware allocators: SPY and SLY. Both techniques modify the RH allocation based on software context switches. SLY improves performance for single-processor systems, but dramatically degrades it for two-CPU systems. SPY can improve performance for both one- and two-processor systems, but requires further development to avoid reallocating RH ¿too soon¿ and make it more effective for multi-processors.