Dynamic Heap Management in High-Level Synthesis for Many-Accelerator Architectures

Dynamic Memory Management (DMM) in High-Level Synthesis has been introduced as a promising solution for optimizing the accelerators' memory usage and reducing the occupied on-chip area. Schemes for dynamic memory allocation have been suggested for many-accelerator architectures where memory sharing and resource reusing has the potential to increase the number of synthesized accelerators, rising the throughput per Watt ratio. However, in those architectures, the simultaneous execution of many accelerators may reduce memory efficiency, increasing the Memory Allocation Failures (MAFs) as a consequence of the sub-optimal utilization of the shared memories. MAFs due to memory fragmentation can reach up to 38.5% of the overall memory allocation failures when accelerators with heterogeneous allocation sizes are executed in parallel in a shared memory space. In this manuscript we propose an HLS methodology for minimizing MAFs for many-accelerator DMM frameworks that are caused by on-chip inefficient memory utilization. Our proposed methodology is orthogonal to the static memory allocation techniques of the Xilinx Vitis suite and was evaluated using Xilinx Vitis/Vitis HLS 2020.1 on an Alveo U200 FPGA device as an extension of the Memluv DMM framework. In the experimental results we show that our proposed methodology may decrease up to 38.5% the MAFs due to fragmentation and up to 91% the overall allocation fails with a controllable increase on the utilized resources and a on the accelerators' latency.