Widening resources: a cost-effective technique for aggressive ILP architectures

The inherent instruction-level parallelism (ILP) of current applications (specially those based on floating point computations) has driven hardware designers and compilers writers to investigate aggressive techniques for exploiting program parallelism at the lowest level. To execute more operations per cycle, many processors are designed with growing degrees of resource replication (buses and functional units). However the high cost in terms of area and cycle time of this technique precludes the use of high degrees of replication. An alternative to resource replication is resource widening, that has also been used in some recent designs, in which the width of the resources is increased. In this paper we evaluate a broad set of design alternatives that combine both replication and widening. For each alternative we perform an estimation of the ILP limits (including the impact of spill code for several register file configurations) and the cost in terms of area and access time of the register file. We also perform a technological projection for the next 10 years in order to foresee the possible implementable alternatives. From this study we conclude that if the cost is taken into account, the best performance is obtained when combining certain degrees of replication and widening in the hardware resources. The results have been obtained from a large number of inner loops from numerical programs scheduled for VLIW architecturesPeer ReviewedPostprint (published version

A Survey of Techniques for Architecting TLBs

“Translation lookaside buffer” (TLB) caches virtual to physical address translation information and is used in systems ranging from embedded devices to high-end servers. Since TLB is accessed very frequently and a TLB miss is extremely costly, prudent management of TLB is important for improving performance and energy efficiency of processors. In this paper, we present a survey of techniques for architecting and managing TLBs. We characterize the techniques across several dimensions to highlight their similarities and distinctions. We believe that this paper will be useful for chip designers, computer architects and system engineers

Increasing TLB reach using TCAM cells

We propose dynamic aggregation of virtual tags in TLB to increase its coverage and improve the overall miss ratio during address translation. Dynamic aggregation exploits both the spatial and temporal locality inherent in most application programs. To support dynamic aggregation, we introduce the use of ternary-CAM (TCAM) cells at the second-level TLB. The modified TLB architecture results in an increase of TLB reach without additional CAM entries. We also adopt bulk prefetching concurrently with aggregation technique to enhance the benefits due to spatial locality. The performance of the proposed TLB architecture is evaluated using SPEC2000 benchmarks concentrating on those that show high data TLB miss ratios. Simulation results indicate a reduction in miss ratios between 59% and 99.99% for all the considered bench-marks except for one benchmark, which has a reduction of 10%. We show that the L2 TLB when enhanced using TCAM cells is an attractive solution to high miss ratios exhibited by applications

High-bandwidth address translation for multiple-issue processors

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A DYNAMIC HETEROGENEOUS MULTI-CORE ARCHITECTURE

Ph.DDOCTOR OF PHILOSOPH

Efficient hardware for low latency applications

The design and development of application specific hardware structures has a high degree of complexity. Logic resources are nowadays often not the limit anymore, but the development time. The first part presents a generator which allows defining control and status structures for hardware designs using an abstract high level language. A novel method to inform host systems very efficiently about changes in the register files is presented in the second part. It makes use of a microcode programmable hardware unit. In the third part a fully pipelined address translation mechanism for remote memory access in HPC interconnection networks is presented, which features a new concept to resolve dependency problems. The last part of this thesis addresses the problem of sending TCP messages for a low latency trading application using a hybrid TCP stack implementation that consists of hardware and software components. Furthermore, a simulation environment for the TCP stack is presented

Reducing exception management overhead with software restart markers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 181-196).Modern processors rely on exception handling mechanisms to detect errors and to implement various features such as virtual memory. However, these mechanisms are typically hardware-intensive because of the need to buffer partially-completed instructions to implement precise exceptions and enforce in-order instruction commit, often leading to issues with performance and energy efficiency. The situation is exacerbated in highly parallel machines with large quantities of programmer-visible state, such as VLIW or vector processors. As architects increasingly rely on parallel architectures to achieve higher performance, the problem of exception handling is becoming critical. In this thesis, I present software restart markers as the foundation of an exception handling mechanism for explicitly parallel architectures. With this model, the compiler is responsible for delimiting regions of idempotent code. If an exception occurs, the operating system will resume execution from the beginning of the region. One advantage of this approach is that instruction results can be committed to architectural state in any order within a region, eliminating the need to buffer those values. Enabling out-of-order commit can substantially reduce the exception management overhead found in precise exception implementations, and enable the use of new architectural features that might be prohibitively costly with conventional precise exception implementations. Additionally, software restart markers can be used to reduce context switch overhead in a multiprogrammed environment. This thesis demonstrates the applicability of software restart markers to vector, VLIW, and multithreaded architectures. It also contains an implementation of this exception handling approach that uses the Trimaran compiler infrastructure to target the Scale vectorthread architecture. I show that using software restart markers incurs very little performance overhead for vector-style execution on Scale.(cont.) Finally, I describe the Scale compiler flow developed as part of this work and discuss how it targets certain features facilitated by the use of software restart markersby Mark Jerome Hampton.Ph.D