CABLE: A CAche-Based Link Encoder for Bandwidth-Starved Manycores

Tri Minh Nguyen, Adi Fuchs, David Wentzlaff

Abstract: Off-chip bandwidth is a scarce resource in modern processors, and it is expected to become even more limited on a per-core basis as we move into the era of high-throughput and massively-parallel computation. One promising approach to overcome limited bandwidth is off-chip link compression. Unfortunately, previously proposed latency-driven compression schemes are not a good fit for latency-tolerant manycore systems, and they often do not have the dictionary capacity to accommodate more than a few concurrent threads. In this work, we present CABLE, a novel CAche-Based Link Encoder that enables point-to-point link compression between coherent caches, re-purposing the data already stored in the caches as a massive and scalable dictionary for data compression. We show the broad applicability of CABLE by applying it to two critical off-chip links: (1) the memory link interface to off-chip memory, and (2) the cache-coherent link between processors in a multi-chip system. We have implemented CABLE's search pipeline hardware in Verilog using the OpenPiton framework to show its feasibility. Evaluating with SPEC2006, we find that CABLE increases effective off-chip bandwidth by 7.2× and system throughput by 3.78× on average, 83% and 258% better than CPACK, respectively.