Hardware Task Scheduling for Partially Reconfigurable FPGAs

Abstract

Abstract. Partial reconfiguration (PR) of FPGAs can be used to dynamically extend and adapt the functionality of computing systems, swapping in and out HW tasks. To coordinate the on-demand task execution, we propose and implement a run time system manager for scheduling software (SW) tasks on available processor(s) and hardware (HW) tasks on any number of reconfigurable regions of a partially reconfigurable FPGA. Fed with the initial partitioning of the application into tasks, the corresponding task graph, and the available task mappings, the RTSM considers the runtime status of each task and region, e.g. busy, idle, scheduled for reconfiguration/execution etc., to execute tasks. Our RTSM supports task reuse and configuration prefetching to minimize reconfigurations, task movement among regions to efficiently manage the FPGA area, and RR reservation for future reconfiguration and execution. We validate its correctness using our RTSM to execute an image processing application on a ZedBoard platform. We also evaluate its features within a simulation framework, and find that despite the technology limitations, our approach can give promising results in terms of quality of scheduling. IntroductionReconfiguration can dynamically adapt the functionality of hardware systems by swapping in and out HW tasks. To select the proper resource for loading and triggering HW task reconfiguration and execution in partially reconfigurable systems with FPGAs, efficient and flexible runtime system support is needed [6]. In this paper we propose and implement a Run-Time System Manager (RTSM) incorporating efficient scheduling mechanisms that balance effectively the execution of HW and SW tasks and the use of physical resources. We aim to execute as fast as possible a given application, without exhausting the physical resources. Our motivation during the development of RTSM was to find ways to overcome the strict technology restrictions imposed by the Xilinx PR flow [8]:  Static partitioning of the reconfigurable surface in reconfigurable regions (RR).

FPGA Dynamic and Partial Reconfiguration

“…Much of the work on automated partitioning tries to schedule a graph of dependent tasks onto a fixed number of regions, minimising runtime [Ayadi et al 2014;Charitopoulos et al 2015;Purgato et al 2016]. They assume that multiple FPGA regions are used similar to a multi-processor system with each region processing an independent task.…”

“…Another more practical solution is to floorplan the FPGA and generate bitstreams for all tasks at all possible PRRs and store them in a database. The scheduler can then load the correct bitstream when a task is scheuled to a particular PRR [Charitopoulos et al 2015]. This scheduling can be either online or offline and the scheduler can abide by hard real-time requirements where present.…”

Operating System Concepts for Reconfigurable Computing: Review and Survey

“…As extracting the current content of all memory elements of a reconfigurable area is not that easy on commercial FPGAs, the single-tasking approach is commonly used. However, some publications provide a dedicated mechanism for "context" extraction and restoration of their reconfigurable modules to allow multitasking (cooperative (ReconOS [24], OS4RS [25]) or preemptive (RTSM [26])) approaches. Further discussions of details on possible hw-context switching strategies can be found in [27,28].…”

“…was developed at the Technical University of Crete (Greece) and is presented in [26]. The RTSM manages physical resources employing scheduling and placement algorithms to select the appropriate hw processing element (PE), that is, a reconfigurable area, to load and execute a particular hwtask, or to activate a software-processing element (CPU) for executing the SW version of a task.…”

A Unified Hardware/Software Monitoring Method for Reconfigurable Computing Architectures Using PAPI

“…The tasks of hardwareabstraction and resource-access-standardization are usually carried out by an Operating System (OS). This issue has been addressed by different research groups and different solutions have been proposed: a Run-Time System Manager (RTMS) [12] by Technical University of Crete; SPREAD [13], a Streaming-Based Partially Reconfigurable Architecture and Programming Model proposed by Wang et al; FUSE [14], a Front-end USEr framework developed in Canada at the Simon Fraser University are some of the latest frameworks and OS extensions that target reconfigurable platforms.…”