Maintaining coherence in large-scale chip multiprocessors (CMPs) embodies tremendous design trade-offs in meeting the area, energy and performance requirements. Sparse directory organizations represent the most energy-efficient and scalable approach towards many-core coherence. However, their limited associativity disallows the one-to-one correspondence of directory entries to cached blocks, rendering them inadequate in tracking all cached blocks. Unless the directory storage is generously over-provisioned, conflicts will force frequent invalidations of cached blocks, severely jeopardizing the system performance. As the chip area and power become increasingly precious with the growing core count, over-provisioning the directory storage becomes unsustainably costly. Stash Directory is a novel sparse directory design that allows directory entries tracking private blocks to be safely evicted without invalidating the corresponding cached blocks. By doing so, it improves system performance and increases the effective directory capacity, enabling significantly smaller directory designs. To ensure correct coherence under the new relaxed inclusion property, stash directory delegates to the last level cache the responsibility to discover hidden cached blocks when necessary, without however raising significant overhead concerns. Simulations on a 16-core CMP model show that Stash Directory can reduce space requirements to 1/8 of a conventional sparse directory, without compromising performance.

Predicting target processors that a coherence request must be delivered to can improve the miss handling latency in shared memory systems. In directory coherence protocols, directly communicating with the predicted processors avoids costly indirection to the directory. In snooping protocols, prediction relaxes the high bandwidth requirements by replacing broadcast with multicast. In this work, we propose a new run-time coherence target prediction scheme that exploits the inherent correlation between synchronization points in a program and coherence communication. Our workload-driven analysis shows that by exposing synchronization points to hardware and tracking them at run time, we can simply and effectively track stable and repetitive communication patterns. Based on this observation, we build a predictor that can improve the miss latency of a directory protocol by 13%. Compared with existing address- and instruction-based prediction techniques, our predictor achieves comparable performance using substantially smaller power and storage overheads.

Abstract Simulation is indispensable in computer architecture research. Researchers increasingly resort to detailed architecture simulators to identify performance bottlenecks, analyze interactions among different hardware and software components, and measure the impact of new design ideas on the system performance. However, the slow speed of conventional execution‐driven architecture simulators is a serious impediment to obtaining desirable research productivity. This paper describes a novel fast multicore processor architecture simulation framework calledTwo‐Phase Trace‐driven Simulation(TPTS), which splits detailed timing simulation into a trace generation phase and a trace simulation phase. Much of the simulation overhead caused by uninteresting architectural events is only incurred once during the cycle‐accurate simulation‐based trace generation phase and can be omitted in the repeated trace‐driven simulations. We report our experiences withtsim, an event‐driven multicore processor architecture simulator that models detailed memory hierarchy, interconnect, and coherence protocol based on the TPTS framework. By applying aggressive event filtering,tsimachieves an impressive simulation speed of 146 millions of simulated instructions per second, when running 16‐thread parallel applications. Copyright © 2010 John Wiley & Sons, Ltd.

As the Internet grows, both the number of rules in packet filtering databases and the number of prefixes in IP lookup tables inside the router are growing. The packet processing engine is a critical part of the Internet router as it is used to perform packet forwarding (PF) and packet classification (PC). In both applications, processing has to be at wire speed. It is common to use hash-based schemes in packet processing engines; however, the downside of classic hashing techniques such as overflow and worst case memory access time, has to be dealt with. Implementing hash tables using set associative memory has the property that each bucket of a hash table can be searched in one memory cycle outperforming the conventional Ternary CAMs in terms of power and scalability.

The slow speed of conventional execution-driven architecture simulators is a serious impediment to obtaining desirable research productivity. This paper proposes and evaluates a fast manycore processor simulation framework called two-phase trace-driven simulation (TPTS), which splits detailed timing simulation into a trace generation phase and a trace simulation phase. Much of the simulation overhead caused by uninteresting architectural events is only incurred once during the trace generation phase and can be omitted in the repeated trace-driven simulations. We design and implement tsim, an event-driven manycore processor simulator that models detailed memory hierarchy, interconnect, and coherence protocol models based on the proposed TPTS framework. By applying aggressive event filtering, tsim achieves an impressive simulation speed of 146 MIPS, when running 16-thread parallel applications.