What the Blog is About

I am 3rd year PhD Student at the University of Utah. During the course of research we read an incredible amount of research papers, and yet forget most of what we've read. The blog is an attempt to maintain that information easily.

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Fundamental Latency Trade-offs in Architecting DRAM Caches (Alloy Cache)

Authors: Moinuddin K. Qureshi and Gabriel H. Loh Venue:    MICRO 2012 The authors present a new architecture for DRAM cache which targets optimizing latency rather than hit rate. The authors show that for every optimization made to improve hit rate, one must also consider the added cache latency, thus resulting in a new "break even hit rate". The authors compare to three key baselines: an infeasibly large SRAM-tag array, the prior "LH-Cache", and a ideal latency-optimized cache. They find that "unoptimizations" improve latency, while minimally impacting hit-rate. Their final result is a cache which boosts performance 35% improvement over the baseline, and nearly 20% better than the previous LH-cache. The specific contributions are: Moving to a direct mapped cache provides significant improvement (by reducing latency) Combining tag-store and data-store into a single entity improves performance 21% Implementing a small per-core predictor enhances per...
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Continuous Control with Deep Reinforcement Learning (DDPG)

Authors: Timothy P. Lillicrap, Jonathan J. Hunt, Alexander Pritzel, Nicholas Heess, Tom Erez, Yuval Tassa, David Silver, & Daan Wierstra Venue: ICLR 2016 This work focuses on solving the problem of an complex environment AND complex actions. Formally, the work presents "an actor-critic, model-free algorithm based on the deterministic policy gradient (DPG) that can operate over continuous action spaces". This work builds on to two prior works, namely the Deep Q Network (DQN) and DPG algorithm. While DQN proposed using a deep neural network to enable RL to perform well in more complex tasks, it suffers from instability in large action spaces. Orthogonally, DPG offers a solution to large action spaces, but cannot support use of a deep network. This work extends DPG such to fix the instability issues by adding batch normalization and a target network. Batch normalization normalizes each dimension such that samples in a minibatch have a unit mean and variance. The target ne...
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Communist, Utilitarian, and Capitalist Cache Policies on CMPs: Caches as a Shared Resource

Authors:  Lisa R. Hsu, Steven Reinhardt (U Michigan), Ravi Iyer, Srihari Makinei (Intel) Venue:     PACT 2006 This paper examines the resultant partition of different LLC cache allocation policies on an multi-core (CMP) system. The overall finding is that while LRU-like policies tend to degrade into something like utilitarian policies. While at first glance this is may sound good, the metric of utility is raw-IPC, which gives bias toward program with high levels of ILP. The paper also explains that utilitarian policies can result in bad fairness, and likewise fairness policies can result in poor utility. Additionally, the paper goes on to show that different metrics (raw-IPC, misses-per-access, misses-per-instruction) result in drastically different cache partitioning schemes. The paper is more a case study than a proposed solution, and suggest that a more complicated, online policy will be required to target either utility- or fairness-based cache partitioning sc...
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