Original 45nm Intel® Core™ Microarchitecture

Power Improvements on 2008 Desktop Platforms

Introduction

Desktop platforms are experiencing an evolution in what is seen as their primary value to consumers. Until recently, the quest has been exclusively directed at achieving higher and higher workload performance at lower and lower cost to the end user. However, driven by concerns over the environment and greenhouse gas emissions and the increasing importance of Energy Star compliance [1,2], the focus is shifting from the exclusive pursuit of performance and cost improvements to energy-efficient performance (EEP) [3,4] . EEP is the intersection of performance or capabilities with the delivery of those capabilities, using the least amount of energy. In simple terms, for many workloads, this can mean getting the job done as fast as possible and then getting the system into an idle or low-power state. Most of a system's time over the course of a day is spent at or near idle utilization and power levels, as demonstrated in (Figure 1).

Figure 1: System power levels during a 9-hour workday following the EEP 2.0 Model demonstrate that 75 percent of time is at or very near idle utilization

The EEP 2.0 workday, the source of the data in (Figure 1) , assumes several hours of work represented by runs of the productivity benchmark Sysmark 2007 (which has idle time built into it), followed by idle in the form of an employee break, and by some sleep time on longer breaks [3,4] .

Considering all the time the system is less than 10 percent used in any given workday, and that the system is likely to be idle or asleep overnight (unless it is in a batch environment), it is important to focus our attention on idle and low-utilization power improvements. The fact that most desktop platforms are lightly loaded most of the time coupled with the Energy Star Version 4.0 [5] focus on idle power is key to understanding the motivation behind many of the platform power-management features implemented on our 2008 desktop platforms. Idle is defined as the average state of the platform after the operating system (OS) has loaded and the system has been given adequate time to quiesce any activities (15min in the Energy Star Version 4 specification). Without getting too deep into the topics of ACPI and OS power management, readers are encouraged to reference the ACPI 3.0a specification and the Windows* power-management whitepaper for more background information on idle and processor power states [6] . These are shown in (Figure 2) .

Figure 2: Processor/platform power states from the ACPI 3.0a specification

In order to better understand what techniques are required to deliver the most energy-efficient desktop platforms, it is important to first understand where all the power goes in a typically configured desktop platform. Throughout, we focus our attention on a typically configured Intel® vPro™ desktop platform with integrated graphics. ((Figure 3) shows a typical platform hierarchy with the key components.)

Figure 3: Key components in a 2007 corporate platform built with Q35 Express Chipset GMCH and ICH9

We focus on integrated graphics primarily because discrete graphics cards cover a very wide range of power, and the performance extracted from this additional power is not typically necessary for office- or productivity-type applications such as Outlook*, PowerPoint* or Excel* (while energy efficiency is quickly becoming a key attribute for these platforms).

All of the components and their interfaces shown in (Figure 3) are powered either directly from the silver box power supply (as is the case for peripherals such as serial advanced technology attachment, or SATA, drives) or through voltage regulators (VRs) built into the desktop motherboard. For example, in the current platform generation, the processor has at least three individual power rails (core, front-side bus (FSB), and phase locked loop (PLL) supplies); the graphics and memory controller hub (GMCH) may have up to five supply voltages (many of which are shared across various regulators); the I/O controller hub (ICH) has seven individual rails; and dual data rate (DDR) memory requires three rails. All of these component supplies are derived from either a dedicated 12-V processor rail or from the 12-V/3.3-V/5-V rails out of the silver box power supply utilizing about fourteen separate regulators (more if the platform supports the manageability engine, a key component of Active Management Technology). With all of this voltage regulation on a desktop motherboard, it is clear that power delivery is one of the biggest sources of efficiency losses in a platform. Some components may have three voltage regulation steps from AC to final DC supply, prior to the voltage being seen by the silicon. Each such stage loses a little power in the translation.

The pie chart in (Figure 4) demonstrates the areas that we need to focus on to maximize energy efficiency in desktop platforms. Power delivery conversion losses, major platform silicon components (processor, GMCH, and ICH silicon), and SATA hard drives are among the primary power consumers in a desktop platform.

Figure 4: Approximate component power consumption (including losses) for a 45-W AC idle platform

Throughout the remainder of this paper we describe several power innovations on the corporate desktop platform based on the Intel Q45 Express Chipset and the latest Intel processors based on original Intel Core™2 Quad, 45nm microarchitecture. We explore innovations in efficiency through the use of phase shedding on the processor VR. We also look at the impact on idle and active power from deploying deeper C-states than those deployed in previous-generation Intel Q35 chipset-based platforms. We demonstrate some common issues that USB devices present for platform power management and explore solutions and best known practices already in use on mobile platforms. Further, we explore how to get the most out of these improvements with the right OS configuration settings.

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