Cache Equalizer: A Cache Pressure Aware Block Placement Scheme for Large-Scale Chip Multiprocessors

This paper describes Cache Equalizer (CE), a novel distributed cache management scheme for large scale chip multiprocessors (CMPs). Our work is motivated by large asymmetry in cache sets usages. CE decouples the physical locations of cache blocks from their addresses for the sake of reducing misses caused by destructive interferences. Temporal pressure at the on-chip last-level cache, is continuously collected at a group (comprised of cache sets) granularity, and periodically recorded at the memory controller to guide the placement process. An incoming block is consequently placed at a cache group that exhibits the minimum pressure. CE provides Quality of Service (QoS) by robustly offering better performance than the baseline shared NUCA cache. Simulation results using a full-system simulator demonstrate that CE outperforms shared NUCA caches by an average of 15.5% and by as much as 28.5% for the benchmark programs we examined. Furthermore, evaluations manifested the outperformance of CE versus related CMP cache designs

Enabling Fine-Grain Restricted Coset Coding Through Word-Level Compression for PCM

Phase change memory (PCM) has recently emerged as a promising technology to meet the fast growing demand for large capacity memory in computer systems, replacing DRAM that is impeded by physical limitations. Multi-level cell (MLC) PCM offers high density with low per-byte fabrication cost. However, despite many advantages, such as scalability and low leakage, the energy for programming intermediate states is considerably larger than programing single-level cell PCM. In this paper, we study encoding techniques to reduce write energy for MLC PCM when the encoding granularity is lowered below the typical cache line size. We observe that encoding data blocks at small granularity to reduce write energy actually increases the write energy because of the auxiliary encoding bits. We mitigate this adverse effect by 1) designing suitable codeword mappings that use fewer auxiliary bits and 2) proposing a new Word-Level Compression (WLC) which compresses more than 91% of the memory lines and provides enough room to store the auxiliary data using a novel restricted coset encoding applied at small data block granularities. Experimental results show that the proposed encoding at 16-bit data granularity reduces the write energy by 39%, on average, versus the leading encoding approach for write energy reduction. Furthermore, it improves endurance by 20% and is more reliable than the leading approach. Hardware synthesis evaluation shows that the proposed encoding can be implemented on-chip with only a nominal area overhead.Comment: 12 page

Exploratory Efforts to Manage Power-Aware Memories using Software Generated Hints

This report presents our exploratory efforts for managing main memory power-aware chips. Current state-of-the-art power-aware DRAM chips offer various power modes (active, standby, nap, and powerdown) in order to provide a potential to limit power consumption in the face of increasing demand for performance. Our goal in this study is to utilize and exploit these various power modes for the most effective main memory power management under software control in response to workloads becoming increasingly memory-intensive and data-centric

The use of biomaterials for stem cell therapies to prevent myocardial damage post-infarct

This thesis employed a stem cell encapsulating hydrogel patch to increase the amount of beneficial soluble factors that are delivered to the surface of damaged heart tissue following a myocardial infarction. While current medical practices to address the immediate aftermath of a myocardial infarction (MI) have evolved tremendously, there are few, if any, techniques currently administered to slow, cease, or reverse the negative side effects of an occluded artery, such as the replacement of functional myocardium with non-contractile scar tissue. Because of this scar formation, survival of the initial heart attack is commonly accompanied by a decrease in left ventricular functioning due to wall thinning and ventricular enlargement. As a result of the slow, or absent, ability of cardiomyocytes to divide and repopulate the infarcted area, the burden of heart function lies on the surrounding tissue; a load that exhausts the healthy tissue and decreases the quality of life of heart attack survivors. Mesenchymal stem cells (MSCs) have emerged as a promising therapeutic avenue for post-MI treatment, in part due to the “survival signals” that they secrete. Previous work has shown that by increasing the amount of “survival signals” that are introduced to the damaged myocardium, the extent of cardiomyocyte cell death, and subsequent scar formation, can be decreased. While the therapeutic effects of these factors have been documented, one difficulty lies in the ability to maintain a constant flux of secreted factors to the damaged site. This project hypothesized that through the encapsulation of stem cells within an engineered hydrogel construct, the hurdle of soluble factor delivery at the site of injury could be overcome. A constant flux of paracrine factors to the heart surface would allow for cell recruitment to the site(s) of damage, prevention of tissue degradation due to inhospitable environments, and promotion of neovascularizion for sustainable tissue regeneration. Using both a chick chorioallantoic membrane assay and a mouse model of MI, the following aims determined: 1) the vascularization potential of an MSC encapsulated patch, 2) the ability to deliver hydrogels containing pro-survival signals to the heart post-MI, and 3) the ability of these factors to decrease scar formation and improve cardiac function following a heart attack. Knowledge gained from this project will provide the basis for designing materials and strategies for similar studies in larger animal models and eventually for human clinical trials. Successful delivery of the MSC encapsulating patch, and subsequent decrease in myocardial degradation, will greatly improve the quality of life scores of individuals who have suffered heart failure. This increase in quality of life will aid in post-MI mobility and decrease the need for more intensive health care following the initial heart attack; overall decreasing the burden a strained heart has on both patients and the healthcare system

Assessing the performance of energy-aware mappings

International audienceWe aim at mapping streaming applications that can be modeled by a series-parallel graph onto a 2-dimensional tiled chip multiprocessor (CMP) architecture. The objective of the mapping is to minimize the energy consumption, using dynamic voltage and frequency scaling (DVFS) techniques, while maintaining a given level of performance, reflected by the rate of processing the data streams. This mapping problem turns out to be NP-hard, and several heuristics are proposed. We assess their performance through comprehensive simulations using the StreamIt workflow suite and randomly generated series-parallel graphs, and various CMP grid sizes

Power-aware Manhattan routing on chip multiprocessors

Nous nous intéressons au routage des communications dans un processeur multi-cœur (CMP). Le but est de trouver un routage valide, c'est-à-dire un routage dans lequel la quantité de données routée entre deux cœurs voisins ne dépasse pas la bande passante maximale, et tel que la puissance dissipée dans les communications est minimale. Nous nous positionnons au niveau système : nous supposons que des applications, sous forme de graphes de tâches, s'exécutent sur le CMP, chaque tâche étant déjà assignée à un cœur. Nous avons donc un ensemble de communications à router entre les cœurs. Nous utilisons un modèle classique, dans lequel la puissance dissipée par un lien de communication est la somme d'une partie statique et d'une partie dynamique, cette dernière dépendant de la fréquence du lien. Cette fréquence est ajustable et proportionnelle à la bande passante. La politique la plus utilisée est le routage XY : chaque communication est en- voyée horizontalement, puis verticalement. Cependant si nous nous autorisons à utiliser les chemins de Manhattan entre la source et la destination, la puissance dissipée peut être considérablement réduite. De plus, il est parfois possible de trouver une solution, alors qu'il n'en existait pas avec un routage XY. Dans ce papier, nous comparons le routage XY et le routage via des chemins de Manhattan, aussi bien d'un point de vue théorique que d'un point de vue pratique. Nous considérons deux variantes du routage par chemins de Manhattan : dans un routage à chemin unique, un seul chemin peut être utilisé pour chaque communication, tandis que le routage à chemin multiples nous permet d'éclater une communication et de lui faire emprunter plusieurs routes. Nous établissons la NP-complétude du problème consistant à trouver un routage Manhattan qui minimise la puissance dissipée, exhibons la borne supérieure minimale du ratio entre la puissance dissipée par un routage XY et celle dissipée par un routage Manhattan, et pour terminer, nous effectuons des simulations pour étudier les performances de nos heuristiques de routage Manhattan

Multicast Communication in Circuit-Switched Optical Networks

In this paper we examine the problem of multicast routing in Wavelength-division multiplexed (WDM) optical networks. In particular, we examine wavelength and routing assignment problems in circuit-switched WDM networks. We show that although the routing and wavelength assignment (RWA) problem is NP-complete in general, the wavelength assignment (WA) problem can be solevd in a polynomial time