BILL HSU AND MARC SOSNICK-PÉREZ, DEPARTMENT OF COMPUTER SCIENCE, SAN FRANCISCO STATE UNIVERSITY

Today’s CPUs are capable of supporting realtime audio for many popular applications, but some compute-intensive audio applications require hardware acceleration. This article looks at some realtime sound-synthesis applications and shares the authors’ experiences implementing them on GPUs (graphics processing units).

> Realtime GPU Audio

Related:

GPUs: A Closer Look

Computing without Processors

Realtime Computer Vision with OpenCV

MARK CAVAGE

Distributed systems are difficult to understand, design, build, and operate. They introduce exponentially more variables into a design than a single machine does, making the root cause of an application problem much harder to discover. It should be said that if an application does not have meaningful SLAs (service-level agreements) and can tolerate extended downtime and/or performance degradation, then the barrier to entry is greatly reduced. Most modern applications, however, have an expectation of resiliency from their users, and SLAs are typically measured by “the number of nines” (e.g., 99.9 or 99.99 percent availability per month). Each additional 9 becomes harder and harder to achieve.

> There’s Just No Getting around It: You’re Building a Distributed System

Related:

Distributed Computing Economics

Condos and Clouds

Monitoring and Control of Large Systems with MonALISA

DAN GEER

What is critical? To what degree is critical defined as a matter of principle, and to what degree is it defined operationally? I am distinguishing what we say from what we do.

Mainstream media love to turn a spotlight on anything they can label “hypocrisy,” the Merriam-Webster unabridged dictionary meaning of which is:

the act or practice of pretending to be what one is not or to have principles or beliefs that one does not have, especially the false assumption of an appearance of virtue

> Resolved: the Internet Is No Place for Critical Infrastructure

GEORGE NEVILLE-NEIL

Dear KV,

I’ve spent the past three weeks trying to cherry-pick changes out of one branch into another. When do I just give up and merge?

In the Pits

Dear Pits,

I once rode home with a friend from a computer conference in Monterey. It just so happened that this friend is a huge fan of fresh cherries, and when he saw a small stand selling baskets of them he stopped to buy some. Another trait this friend possesses is that he can’t ever pass up a good deal. So while haggling with the cherry seller, it became obvious that buying a whole flat of cherries would be a better deal than buying a single basket, even though that was all we really wanted. Not wanting to pass up a deal, however, my friend bought the entire flat and off we went—eating and talking. It took another 45 minutes to get home, and during that time we had eaten more than half the flat of cherries. I couldn’t look at anything even remotely cherry-flavored for months; and today, when someone says “cherry-picking,” that doesn’t conjure up happy images of privileged kids playing farmer on Saturday mornings along the California coast—I just feel ill.

Cherry-picking and the Scientific Method

ADAM H. LEVENTHAL

In the past five years, flash memory has progressed from a promising accelerator, whose place in the data center was still uncertain, to an established enterprise component for storing performance-critical data. It’s rise to prominence followed its proliferation in the consumer world and the volume economics that followed. With SSDs (solid-state devices), flash arrived in a form optimized for compatibility—just replace a hard drive with an SSD for radically better performance. But the properties of the NAND flash memory used by SSDs differ significantly from those of the magnetic media in the hard drives they often displace. While SSDs have become more pervasive in a variety of uses, the industry has only just started to design storage systems that embrace the nuances of flash memory. As it escapes the confines of compatibility, significant improvements in performance, reliability, and cost are possible.

A File System All Its Own

Related:

Anatomy of a Solid-state Drive

Enterprise SSDs

Flash Disk Opportunity for Server Applications

PETER BAILIS AND ALI GHODSI, UC BERKELEY

In a July 2000 conference keynote, Eric Brewer, now VP of engineering at Google and a professor at the University of California, Berkeley, publicly postulated the CAP (consistency, availability, and partition tolerance) theorem, which would change the landscape of how distributed storage systems were architected.⁸ Brewer’s conjecture—based on his experiences building infrastructure for some of the first Internet search engines at Inktomi—states that distributed systems requiring always-on, highly available operation cannot guarantee the illusion of coherent, consistent single-system operation in the presence of network partitions, which cut communication between active servers. Brewer’s conjecture proved prescient: in the following decade, with the continued rise of large-scale Internet services, distributed-system architects frequently dropped “strong” guarantees in favor of weaker models—the most notable being eventual consistency.

Eventual Consistency Today:
Limitations, Extensions, and Beyond

LATANYA SWEENEY

Do online ads suggestive of arrest records appear more often with searches of black-sounding names than white-sounding names? What is a black-sounding name or white-sounding name, anyway? How many more times would an ad have to appear adversely affecting one racial group for it to be considered discrimination? Is online activity so ubiquitous that computer scientists have to think about societal consequences such as structural racism in technology design? If so, how is this technology to be built? Let’s take a scientific dive into online ad delivery to find answers.

“Have you ever been arrested?” Imagine this question appearing whenever someone enters your name in a search engine. Perhaps you are in competition for an award, a scholarship, an appointment, a promotion, or a new job, or maybe you are in a position of trust, such as a professor, a physician, a banker, a judge, a manager, or a volunteer. Perhaps you are completing a rental application, selling goods, applying for a loan, joining a social club, making new friends, dating, or engaged in any one of hundreds of circumstances for which someone wants to learn more about you online. Appearing alongside your list of accomplishments is an advertisement implying you may have a criminal record, whether you actually have one or not. Worse, the ads may not appear for your competitors.

> Discrimination in Online Ad Delivery

Related:

PATRICK MEENAN

The overwhelming evidence indicates that a Web site’s performance (speed) correlates directly to its success, across industries and business metrics. With such a clear correlation (and even proven causation), it is important to monitor how your Web site performs. So, how fast is your Web site?

First, it is important to understand that no single number will answer that question. Even if you have defined exactly what you are trying to measure on your Web site, performance will vary widely across your user base and across the different pages on your site.

We will discuss active testing techniques that have traditionally been used, then explain newer technologies that permit the browser to report accurate timing data to the server.

How Fast is Your Web Site?

Related:

High Performance Web Sites

Building Scalable Web Services

Improving Performance on the Internet

Queue Portrait: Ang Cui

DAVID F. BACON, RODRIC RABBAH, SUNIL SHUKLA, T.J. WATSON RESEARCH CENTER

When looking at how hardware influences computing performance, we have GPPs (general-purpose processors) on one end of the spectrum and ASICs (application-specific integrated circuits) on the other. Processors are highly programmable but often inefficient in terms of power and performance. ASICs implement a dedicated and fixed function and provide the best power and performance characteristics, but any functional change requires a complete (and extremely expensive) re-spinning of the circuits.

Fortunately, several architectures exist between these two extremes. PLDs (programmable logic devices) are one such example, providing the best of both worlds. They are closer to the hardware and can be reprogrammed.

FPGA Programming for the Masses

Related:

Abstraction in Hardware System Design

Computing without Processors

Of Processors and Processing