f-DSM: An FPGA-Accelerated Distributed Shared Memory for Heterogeneous Instruction-Set-Architecture Hardware

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Virginia Tech


Due to the diminishing relevance of Moore's Law, traditional multi-core systems are increasingly struggling to meet the computational demands of many emerging workloads. Heterogeneous computing, which involves exploiting higher degrees of parallelism (e.g., GPUs) and application-specific specialization (e.g., FPGAs), is increasingly used to meet this demand. An important architectural trend in this space involves using instruction-set-architecture (ISA) heterogeneity. An exemplar case is emerging I/O devices that include CPU cores with ISAs (e.g., ARM, RISC-V) that differ from that of host CPUs (e.g., x86) and have physically discrete memory. Shared-memory programming of such systems requires the Dis- tributed Shared Memory (DSM) abstraction. Software DSM incurs significant OS overhead for maintaining memory coherency. Despite outperforming software predecessors, hardware DSM and cache-coherent interfaces require custom chips and lack the flexibility to experiment with different DSM consistency protocols. This thesis presents fDSM, an FPGA-accelerated DSM framework for ISA-heterogeneous hardware. fDSM implements a high-speed messaging layer to enable inter-node communication across ISA-different CPU cores and a DSM protocol processor that maintains virtual memory coherency using a multiple-reader single- writer DSM algorithm. Experimental studies reveal that fDSM outperforms prior art, including Popcorn Linux's software DSM abstraction, which uses TCP-IP and state-of-the-art Infiniband RDMA messaging layers by 2.8X and 7%, respectively. fDSM also provides reconfigurability and thereby allows implementation and experimentation of different memory consistency models.



Distributed Shared Memory, Sequential Consistency, Popcorn Linux, Field programmable gate arrays, Instruction-Set-Architecture