Intel DMA Coalescing White Paper

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Intel

I350 Ethernet Controller and

DMA Coalescing

Intel® Ethernet Power Management Technology with DMA Coalescing enables users to determine how to meet their

energy efciency and operational goals.

Power Management Technology

Intel’s Power Management Technology

(PMT) is a standards-based solution,

leveraging existing ACPI* and PCI*

standards, as well as existing platform

power management capabilities of the

CPU, chipset and operating system.

PMT provides solutions to common power

management approaches by:

• Reducing idle power

• Reducing capacity and power as a

function of demand

• Whenever possible, operating at

maximum energy efciency

• Enabling functionality only when needed

Reducing Idle Power

With the Intel® I350-based network

controllers and adapters, integrated

quad-port congurations consolidate and

coordinate functionality between ports

on the adapter, effectively increasing

Introduction

Power consumption is a signicant concern for today’s data centers. Power is a monthly

xed cost that all data center providers must pass on to their customers. Competitive

industry-wide pricing pressure requires that data center providers nd intelligent and

creative ways to keep power costs down. In addition, regulatory and OpX factors aimed

at reducing total energy consumption have created a demand for more energy-efcient

computer platforms. Yet, end-users still need the ability to use the peak performance of

their assets to meet business objectives. Energy efciency is not strictly measured by

raw peak or idle power consumption. High performance devices operating at maximum

performance for short durations, and then returning to a low-power idle state, are

typically the most energy efcient congurations. Intel® Ethernet Power Management

Technology with DMA Coalescing enables end-users to make a range of choices to

determine which tradeoffs are acceptable to meet their operational goals.

energy efciency. The Intel® I350 also

supports PCI power management states,

which helps to reduce overall power

consumption by reducing power when a

device is in an idle state.

The I350 also incorporates a high-

efciency integrated switching-voltage

regulator (SVR) that reduces overall BOM

cost and design complexity. Its design also

enables a more efcient power supply to

the component.

Reducing Capacity and Power as a

Function of Demand

Intel’s PMT incorporates IEEE* 802.3az

support, (http://www.ieee802.org/3/az/

index.html) also known as Energy Efcient

Ethernet or EEE.

Studies indicate that the majority of

platforms—both client and server—only

use a fraction of the available bandwidth

of the local link. Ethernet trafc typically

Zane Stabley

Int el Corporation

Carl Hansen

Intel Corporation

“Intel Power Management

Technology with DMA Coalesc-

ing enables end users to make

a range of choices to determine

which trade offs are acceptable

to meet their operational goals.”

WHITE PAPER

Intel® Power Management &

I350 Ethernet Controller

Network Connectivity

Summary of content (6 pages)

PAGE 1
WHITE PAPER Intel® Power Management & I350 Ethernet Controller Network Connectivity Intel® I350 Ethernet Controller and DMA Coalescing Intel® Ethernet Power Management Technology with DMA Coalescing enables users to determine how to meet their energy efficiency and operational goals. Introduction “Intel Power Management Technology with DMA Coalescing enables end users to make a range of choices to determine which trade offs are acceptable to meet their operational goals.
PAGE 2
Intel® I350 Ethernet Controller & DMA Coalescing Table of Contents Verifying Behavior. . . . . . . . . . . . . . . . 5 occurs in bursts, leaving long periods of inactivity. IEEE 802.3az enables the network interface to enter into a LowPower-Idle (LPI) mode when the adapter detects that the network link is not being fully used. This enables link partners to save energy by cycling between active and LPI states. References. . . . . . . . . . . . . . . . . . . . . . .
PAGE 3
Intel® I350 Ethernet Controller & DMA Coalescing Note: One impact of delaying interrupts and DMA operations is an increase in latency. Most (not all) applications are quite tolerant of latency. DMA coalescing is accomplished by using the existing transmit and receive buffers on the LAN device to store packets, rather than immediately transferring packet data to or from host memory (as current LAN solutions do).
PAGE 4
Intel® I350 Ethernet Controller & DMA Coalescing • Set one port as Receive with smartbits = 1514 byte continuous UDP packet stream from another port. • Results & Observations • Throttling interrupts by itself improves power efficiency. • Adding DMA coalescing creates further power savings. Figure 4 shows how moderating interrupts improves power efficiency and the addition of DMA coalescing further increases power savings.
PAGE 5
Intel® I350 Ethernet Controller & DMA Coalescing configuration. DMAC Linux* versions 2.6.33 and later support the required power management hooks to optimize DMA coalescing. Customizations of the kernel enhance the effect: 0, 250, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000 0 (disabled) 1. Enable ‘tickless’ feature with Tick=1000 and preemption mode=Server, CPU idle– Power Management support=enabled. Turning on DMA Coalescing may save energy with kernel 2.6.32 and later.
PAGE 6
Intel® I350 Ethernet Controller & DMA Coalescing Figure 6 C-state entry by the OS is on a per-core basis. These are called “Core C States” (or CC3, for example, for Core C3). When all CPU cores simultaneously go into the same or deeper C state, the supervisory firmware controlling the package (previously called “socket”) can enable the entire package to transition to a Package C state. The dramatic power savings occur whenever the entire package enters these Package C3 or Package C6 states.