Power dissipation and thermal issues are increasingly significant in modern processors. As a result, it is crucial that power/performance tradeoffs be made more visible to chip architects and even compiler writers, in addition to circuit designers. Most existing power analysis tools achieve high accuracy by calculating power estimates for designs only after layout or floorplanning are complete. In addition to being available only late in the design process, such tools are often quite slow, which compounds the difficulty of running them for a large space of design possibilities.This paper presents Wattch, a framework for analyzing and optimizing microprocessor power dissipation at the architecture-level. Wattch is 1000X or more faster than existing layout-level power tools, and yet maintains accuracy within 10% of their estimates as verified using industry tools on leading-edge designs. This paper presents several validations of Wattch's accuracy. In addition, we present three examples that demonstrate how architects or compiler writers might use Wattch to evaluate power consumption in their design process.We see Wattch as a complement to existing lower-level tools; it allows architects to explore and cull the design space early on, using faster, higher-level tools. It also opens up the field of power-efficient computing to a wider range of researchers by providing a power evaluation methodology within the portable and familiar SimpleScalar framework.

Wattch: a framework for architectural-level power analysis and optimizations

With the increasing clock rate and transistor count of today's microprocessors, power dissipation is becoming a critical component of system design complexity. Thermal and power-delivery issues are becoming especially critical for high-performance computing systems. In this work, we investigate dynamic thermal management as a technique to control CPU power dissipation. With the increasing usage of clock gating techniques, the average power dissipation typically seen by common applications is becoming much less than the chip's rated maximum power dissipation. However system designers still must design thermal heat sinks to withstand the worse-case scenario. We define and investigate the major components of any dynamic thermal management scheme. Specifically we explore the tradeoffs between several mechanisms for responding to periods of thermal trauma and we consider the effects of hardware and software implementations. With approximate dynamic thermal management, the CPU can be designed for a much lower maximum power rating, with minimal performance impact for typical applications.

Dynamic thermal management for high-performance microprocessors

The ability to estimate power consumption during early-stage definition and trade-off studies is a key new methodology enhancement Opportunities for saving power can be exposed via microarchitecture-level modeling, particularly through clock-gating and dynamic adaptation In this paper we describe the approach of using energy-enabled performance simulators in early design We examine some of the emerging paradigms in processor design and comment on their inherent power-performance characteristics

Power-aware microarchitecture: design and modeling challenges for next-generation microprocessors

This tutorial surveys design methods for energy-efficient system-level design. We consider electronic sytems consisting of a hardware platform and software layers. We consider the three major constituents of hardware that consume energy, namely computation, communication, and storage units, and we review methods of reducing their energy consumption. We also study models for analyzing the energy cost of software, and methods for energy-efficient software design and compilation. This survery is organized around three main phases of a system design: conceptualization and modeling design and implementation, and runtime management. For each phase, we review recent techniques for energy-efficient design of both hardware and software.

/pdf/system-level-power-optimization-techniques-and-tools-58sern1xgm.pdf

System-level power optimization: techniques and tools

We present a new design for a 1-b full adder featuring hybrid-CMOS design style. The quest to achieve a good-drivability, noise-robustness, and low-energy operations for deep submicrometer guided our research to explore hybrid-CMOS style design. Hybrid-CMOS design style utilizes various CMOS logic style circuits to build new full adders with desired performance. This provides the designer a higher degree of design freedom to target a wide range of applications, thus significantly reducing design efforts. We also classify hybrid-CMOS full adders into three broad categories based upon their structure. Using this categorization, many full-adder designs can be conceived. We will present a new full-adder design belonging to one of the proposed categories. The new full adder is based on a novel xor-xnor circuit that generates xor and xnor full-swing outputs simultaneously. This circuit outperforms its counterparts showing 5%-37% improvement in the power-delay product (PDP). A novel hybrid-CMOS output stage that exploits the simultaneous xor-xnor signals is also proposed. This output stage provides good driving capability enabling cascading of adders without the need of buffer insertion between cascaded stages. There is approximately a 40% reduction in PDP when compared to its best counterpart. During our experimentations, we found out that many of the previously reported adders suffered from the problems of low swing and high noise when operated at low supply voltages. The proposed full adder is energy efficient and outperforms several standard full adders without trading off driving capability and reliability. The new full-adder circuit successfully operates at low voltages with excellent signal integrity and driving capability. To evaluate the performance of the new full adder in a real circuit, we embedded it in a 4- and 8-b, 4-operand carry-save array adder with final carry-propagate adder. The new adder displayed better performance as compared to the standard full adders

/pdf/design-of-robust-energy-efficient-full-adders-for-deep-5ba51kaofh.pdf

Design of Robust, Energy-Efficient Full Adders for Deep-Submicrometer Design Using Hybrid-CMOS Logic Style

Power consumption has become one of the biggest challenges in high-performance microprocessor design. The rapid increase in the complexity and speed of each new CPU generation is outstripping the benefits of voltage reduction and feature size scaling. Designers are thus continuously challenged to come up with innovative ways to reduce power, while trying to meet all the other constraints imposed on the design. This paper presents an overview of the issues related to power consumption in the context of Intel CPUs. The main trends that are driving the increased focus on design for low power are described. System and benchmarking issues, and sources of power consumption in a high-performance CPU are briefly described. Techniques that have been tried on real designs in the past are described. The role of CAD tools and their limitations in this domain will also be discussed. In addition, areas that need increased research focus in the future are also pointed out.

/pdf/reducing-power-in-high-performance-microprocessors-58l3hdx0ud.pdf

Reducing power in high-performance microprocessors

It is mid 1998. The Speedy Microsystems design team is discussing a memo they have just received from Marketing about their next generation machine due to tape out in 2000, a 1.5V, lGHz, 100 watt, 40 million transistor superscalar microprocessor with multimedia extensions to be fabricated in O.lSum CMOS. Only one problem. Marketing has just announced a major push into Network Computers, and all of a sudden the power budget has dropped to 4 watts. Including the multimedia extensions and an onchip radio. Worse yet, a major customer has just invented a 50mW color display and is threatening to cancel its $1 billion order unless Speedy can deliver a 1OOmW processor in 18 months. Not only that, Marketing wants to continue pushing forward at the high end because these has been explosive growth in the serves market.

Deo Singh

Papers

Reducing power in high-performance microprocessors

Low power design without compromise (panel)