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Computer Science @ Rochester
Wednesday, April 24, 2013
12:00 AM
CSB 703
Ph.D. Thesis Proposal
Qing Guo
Associative Computing with Resistive Memories
Wednesday, April 24, 2013 12:00PM - 2:00PM CSB 703 Ph.D. Thesis Proposal

Qing Guo University of Rochester

Associative Computing with Resistive Memories

With technology scaling, on-chip power dissipation and off-chip memory bandwidth have become significant performance bottlenecks in virtually all computer systems, from mobile devices to supercomputers. Ternary content addressable memories (TCAM) hold the potential to address both problems in the context of a wide range of data-intensive workloads. Power dissipation is reduced by eliminating instruction processing and data movement overheads present in a purely RAM based system. Bandwidth demand is lowered by processing data directly on the TCAM chip, thereby decreasing off-chip traffic. This thesis first introduces a phase change memory (PCM) based TCAM cell and array architecture that has the potential to scale TCAM capacity from megabytes to gigabytes. High-density resistive TCAM chips are organized into a DDR3-compatible DIMM, and are accessed through a software library with zero modifications to the processor or the motherboard. By tightly integrating TCAM with conventional virtual memory, and by allowing a large fraction of the physical address space to be made content-addressable, the memory system improves average performance by 4× and average energy consumption by 10× on a set of evaluated data-intensive applications. The thesis second demonstrates AC-DIMM--an associative compute engine implemented with spin-torque-transfer magnetoresistive RAM (STT-MRAM). AC-DIMM addresses the limited flexibility of previous TCAM accelerators by combining two powerful capabilities--associative search and processing in memory. Generality is improved by augmenting a TCAM system with a set of integrated, user programmable microcontrollers that operate directly on search results, and by architecting the system such that key-value pairs can be co-located in the same TCAM row. AC-DIMM achieves a 4.2× speedup and a 6.5× energy reduction over a conventional RAM-based system on a set of 13 evaluated applications. High-capacity resistive TCAMs, using either PCM or STT-MRAM, are subject to hard errors and soft errors. Although hard errors are largely caused by writes and can be detected by simply applying a verity-after-write scheme, protecting resistive TCAMs from soft errors is yet an open question. The thesis conducts studies on existing fault tolerant techniques, and proposes two preliminary solutions, one for bit-serial resistive TCAMs and the other for bit-parallel resistive CAMs.