Architecting Optically Controlled Phase Change Memory
Architecting Optically Controlled Phase Change Memory
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设计光控相变存储器
DOI：
10.1145/3533252
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发表时间：
2021-07
影响因子：
1.6
通讯作者：
A. Narayan;Y. Thonnart;P. Vivet;A. Coskun;A. Joshi
中科院分区：
文献类型：
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作者：
A. Narayan;Y. Thonnart;P. Vivet;A. Coskun;A. Joshi
相变存储器(PCM)是一种很有吸引力的主存储器候选者，因为它提供非易失性和零泄漏功率，同时与DRAM相比提供更高的单元密度、更长的数据保持时间和更高的容量扩展。在PCM中，数据以相变材料的晶态或非晶态存储。然而，与DRAM和有限的多电平单元(MLC)容量相比，典型的电控PCM(EPCM)具有更长的写入延迟和更高的写入能量。这些挑战限制了在具有EPCM的计算系统上运行的数据密集型应用程序的性能。最近，研究人员展示了光控PCM(OPCM)单元，支持5比特/单元，而不是EPCM的2比特/单元。这些OPCM单元可以通过光信号直接访问，光信号在高带宽密度的硅-光子链路中被多路复用。与EPCM相比，OPCM中更高的MLC容量和使用光信号的直接信元访问实现了更高的读/写吞吐量和更低的每次访问能量。然而，由于使用光信号的直接单元访问，OPCM系统不能使用传统的存储结构来设计。我们需要根据OPCM技术的特性对存储器架构进行彻底的重新设计。本文提出了一种名为COSMOS的统一网络和主存储系统的设计，该系统将OPCM和硅-光子链路相结合，以实现高存储吞吐量。COSMOS由一个分层的多组OPCM阵列组成，具有新颖的读写访问协议。COSMOS使用电-光-电(E-O-E)控制单元将标准DRAM读/写命令(在电域中发送)从存储控制器映射到访问OPCM单元的光信号。我们对包含处理器和COSMOS的2.5D集成系统的评估显示，与EPCM系统相比，图形和HPC工作负载的平均加速比为2.14倍。与EPCM相比，COSMOS的每位读取能量降低3.8倍，每位写入能量降低5.97倍。COSMOS是第一款非易失性存储器，除了增加位密度、更高的区域效率和改进的可扩展性外，它还提供与DDR5相当的性能和能源消耗。
Phase Change Memory (PCM) is an attractive candidate for main memory, as it offers non-volatility and zero leakage power while providing higher cell densities, longer data retention time, and higher capacity scaling compared to DRAM. In PCM, data is stored in the crystalline or amorphous state of the phase change material. The typical electrically controlled PCM (EPCM), however, suffers from longer write latency and higher write energy compared to DRAM and limited multi-level cell (MLC) capacities. These challenges limit the performance of data-intensive applications running on computing systems with EPCMs. Recently, researchers demonstrated optically controlled PCM (OPCM) cells with support for 5 bits/cell in contrast to 2 bits/cell in EPCM. These OPCM cells can be accessed directly with optical signals that are multiplexed in high-bandwidth-density silicon-photonic links. The higher MLC capacity in OPCM and the direct cell access using optical signals enable an increased read/write throughput and lower energy per access than EPCM. However, due to the direct cell access using optical signals, OPCM systems cannot be designed using conventional memory architecture. We need a complete redesign of the memory architecture that is tailored to the properties of OPCM technology. This article presents the design of a unified network and main memory system called COSMOS that combines OPCM and silicon-photonic links to achieve high memory throughput. COSMOS is composed of a hierarchical multi-banked OPCM array with novel read and write access protocols. COSMOS uses an Electrical-Optical-Electrical (E-O-E) control unit to map standard DRAM read/write commands (sent in electrical domain) from the memory controller on to optical signals that access the OPCM cells. Our evaluation of a 2.5D-integrated system containing a processor and COSMOS demonstrates 2.14 × average speedup across graph and HPC workloads compared to an EPCM system. COSMOS consumes 3.8× lower read energy-per-bit and 5.97× lower write energy-per-bit compared to EPCM. COSMOS is the first non-volatile memory that provides comparable performance and energy consumption as DDR5 in addition to increased bit density, higher area efficiency, and improved scalability.