Click here to close now.

Welcome!

Java Authors: Pat Romanski, Leo Reiter, Elizabeth White, Liz McMillan, Yeshim Deniz

Related Topics: Java

Java: Article

Multi-Core and Massively Parallel Processors

Coming soon to a theater near you...

As software developers we have enjoyed a long trend of consistent performance improvement from processor technology. In fact, for the last 20 years processor performance has consistently doubled about every two years or so. What would happen in a world where these performance improvements suddenly slowed dramatically or even stopped? Could we continue to build bigger and heavier, feature-rich software? Would it be time to pack up our compilers and go home?

The truth is, single threaded performance improvement is likely to see a significant slowdown over the next one to three years. In some cases, single-thread performance may even drop. The long and sustained climb will slow dramatically. We call the cause behind this trend the CLIP level.

  • C - Clock frequency increases have hit a thermal wall
  • L - Latency of processor-to-memory requests continues as a key performance bottleneck
  • IP - Instruction-level Parallelism is already fully exploited by current processor and compiler technologies.
To overcome these challenges the industry is looking to multi-core and multithreaded processor designs to continue the performance improvement trend. These designs don't look to improve the performance of single threads of execution, but instead to run many and sometimes massive numbers of threads in parallel. Wait just a minute though. Is concurrent programming that easy? Hasn't it been tried before?

This article will dive deeper into the current issues challenging processor performance improvement and include a high-level overview of the key microprocessor players: Intel, AMD, Sun, and IBM. Finally, we'll take a deep dive into the challenges, opportunities, and technologies available to Java programmers to take advantage of concurrent programming to leverage these new processor technologies. If you're not programming in parallel today, you will be soon.

Multi-Core Mania
Increases in processor clock frequency are slowing and in many cases are being decreased to reduce power consumption. One trend continues though. The industry continues to shrink the size of transistors, doubling the number of transistors on a chip about every two years or so. In 2007 most major chip manufacturers will begin the shift from a 60nm to a 45nm process. This will yield transistors about 1/2000th the width of a human hair! To provide a relative perspective, a silicon atom itself is about 1/4nm. Obviously continuing to halve the size of transistors will also reach a limit in the not too distant future. But that's a topic for another paper.

So, how will the industry use this new transistor budget to improve processor performance? Techniques such as superscalar execution, pipelining, and speculative processing with branch prediction have added significant complexity to microprocessor designs, but have also been successful at improving performance. Unfortunately, the latency to memory on cache misses and the high frequency of branches in most workloads is proving to be a limiting factor. Building ever-larger caches is one way to mitigate the memory latency problem but as cache size exceeds common working set size, there are rapidly diminishing returns for investing transistors in cache memory.

Instead, the industry is moving toward multi-core, multithreading, and specialization. Instead of improving the performance of a single thread on a single core, the transistor budget is being used to add multiple cores to a single chip. Further, in many cases each core is capable of running multiple threads to hide memory latency. When one thread is blocked by a long latency event, such as a cache miss, the processor simply switches to another thread to execute. Also, many chip designs now include special-purpose processing units that make effective use of transistors for specific tasks such as cryptography.

Taking a closer look at the processors themselves, the IBM Power is distinguished as being the first to introduce multiple cores on a chip in the Power 4 design in 2001. IBM recently introduced the Power 6 processor, which combines two high-performance cores on a chip with each core supporting two-way multithreading. Besides providing multiple cores, the Power 6 also achieved an amazing 4.7GHz clock rate showing that IBM remains serious about single-thread performance while keeping pace with the industry on multi-core. As Power 6 is destined to be included in high-end servers, IBM has also focused heavily on RAS (reliability, availability, serviceability) and virtualization.

In the x86 architecture camp, rivals AMD and Intel have both recently introduced multi-core processors. In 2006, Intel introduced chips with two cores while chips with four cores, based on 45nm technology, shouldappear this year. As part of the move to multi-core, Intel removed support for its version of multithreading known as "hyperthreading," although multithreading is expected to return in future designs. Not to be outdone, AMD later this year, will introduce its first four-core chip known as Barcelona. Both Intel and AMD continue to focus on single-thread performance as well, each introducing new innovations in instruction-level parallelism and caches. One key difference in their designs is the memory bus architecture. Intel is continuing with its symmetric front-side bus architecture. AMD, on the other hand, has introduced a NUMA-based design based on the open Hypertransport technology in hopes of alleviating the memory bus bottleneck.

Sun has adopted a more radical departure in design from prior generations of SPARC. At the end of 2005, Sun released the UltraSPARC T1 or Niagara processor. Niagara includes up to eight cores, significantly more than competing server processors. Sun was able to squeeze eight cores on the chip by shifting focus away from the best achievable single-thread performance toward high chip-level throughput. Niagara cores run at a relatively low clock rate and don't support out-of-order processing, branch prediction, or many other common ILP optimizations. Instead they depend on four-way multithreading to tolerate long waits for memory. The goal is to achieve high overall throughput through application concurrency. However, applications with lower concurrency may run significantly slower on Niagara relative to the other processors described here.

At this point, all of the key players are producing chips with multiple cores but diverging in core design, memory nest, and other important aspects. The key to success for processor designers over the next few years will be in the innovative use of their transistor budget. Architects will make strategic tradeoffs between single-thread performance, massive concurrency, cache sizes, power consumption, and specialized processing units. The companies that make tradeoffs in the most innovative ways to meet the demands of the market should emerge as the winners.

Parallel Programming
As a developer, it will be important for you to learn the skills necessary to develop applications that can run with high performance on these increasingly parallel processors. Since single-thread performance isn't likely to improve at historical rates, the developer will have to look to concurrency to improve performance for a given task. The goal of parallel programming is to reduce the time of a task by dividing it into a set of subtasks that can be processed concurrently. While this may seem simple enough, experience shows that developing correct and effective parallel programs is surprisingly difficult. To utilize parallelism in hardware effectively, software tasks must be decomposed into subtasks, code must be written to coordinate the subtasks and work must be balanced as much as possible. Still sound easy? Read on.

As you get started with parallel programming, the first rule to become familiar with is Amdahl's Law. Amdahl's Law says that speeding up your program is limited by the part that's not running in parallel. For example, if a profile reveals that 20% of the time is spent in code that can only run sequentially on one processor, then the best speed increase you can possibly get, even with perfect parallelization of the rest of your program is 5x, no matter how many processors you throw at it. Load imbalance is a similar problem. If you've divided your code into N subtasks, the time taken to execute them is not 1/N. Rather the time taken is the maximum of the execution times of the subtasks.

If getting your code divided into subtasks and ensuring that work is well balanced sounded hard, then let us introduce you to the coordination problem. Unfortunately, very few programs can be parallelized so simply. The reason is that those subtasks are likely to want to operate on the same data and some of the subtasks may have to wait for others to do their thing before proceeding. It's okay if two subtasks want to read the same memory location in parallel, but if one of them wants to write to the location, you've got trouble because you can't predict which subtask will get to it first.

For example, operations to insert and remove objects from a linked list must be executed so that updates to the data structures happen sequentially and don't corrupt each other. An incorrect ordering of accesses to a memory location is called a data race and it can be one of the most difficult bugs to find because your code might behave differently on each run and might even change once you decide to start debugging. To deal with this problem, most programming environments include mechanisms to ensure that a subtask has exclusive access to specific memory, commonly called locks. Unfortunately locks bring their own unique problems when multiple subtasks compete for access and, if used indiscriminately, can reverse all of your hard work in parallelizing your code by making subtasks wait too often or too long for exclusive access to shared memory.


More Stories By J. Stan Cox

J. Stan Cox is a senior engineer with IBM's WebSphere Application Server performance group. In this role, he has worked to improve WebSphere application performance for J2EE, Web 2.0, Web services, XML and more. His current focus is WebSphere multicore and parallel foundation performance. Stan holds a B.S.C.S from Appalachian State University (1990) and an MS in computer science from Clemson University (1992).

More Stories By Bob Blainey

Bob Blainey is a Distinguished Engineer in the IBM Software Group, responsible for the technical roadmap for software in the era of multi-core and related next-generation systems innovations. Bob is an expert in programming languages and compilers having spent much of his career at IBM driving ever-greater performance and parallelism through program analyses and transformations. Immediately prior to his current position, Bob was CTO for Java at IBM. He is a member of the IBM Academy of Technology, an IBM Master Inventor, and, most impressive of all, manages to remain sane with two pre-teen daughters in the house.

More Stories By Vijay Saraswat

Vijay Saraswat joined IBM Research in 2003 after a year as a professor at Penn State, a couple of years at start-ups, and 13 years at Xerox PARC and AT&T Research. His main interests are in programming languages, constraints, logic, and concurrency. At IBM, he leads the work on the design and implementation of X10, a modern object-oriented programming language intended for scalable concurrent computing. Over the last 20 years he has lectured at most major universities and research labs in U.S.A. and Europe. Vijay got a B Tech degree from the Indian Institute of Technology, Kanpur, and an MS and PhD from Carnegie-Mellon University. His thesis on concurrent constraint programming won the ACM Doctoral Dissertation Award in 1989, and a related paper won a best-paper-in-20-years award in its area.

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Jim Falgout 11/26/07 09:37:55 AM EST

The X10 site does not seem very active. The news feed on the last release is dated December of 2006. Do you have any information on the current state of X10?

@ThingsExpo Stories
GENBAND has announced that SageNet is leveraging the Nuvia platform to deliver Unified Communications as a Service (UCaaS) to its large base of retail and enterprise customers. Nuvia’s cloud-based solution provides SageNet’s customers with a full suite of business communications and collaboration tools. Two large national SageNet retail customers have recently signed up to deploy the Nuvia platform and the company will continue to sell the service to new and existing customers. Nuvia’s capabilities include HD voice, video, multimedia messaging, mobility, conferencing, Web collaboration, deskt...
Sonus Networks introduced the Sonus WebRTC Services Solution, a virtualized Web Real-Time Communications (WebRTC) offer, purpose-built for the Cloud. The WebRTC Services Solution provides signaling from WebRTC-to-WebRTC applications and interworking from WebRTC-to-Session Initiation Protocol (SIP), delivering advanced real-time communications capabilities on mobile applications and on websites, which are accessible via a browser.
Temasys has announced senior management additions to its team. Joining are David Holloway as Vice President of Commercial and Nadine Yap as Vice President of Product. Over the past 12 months Temasys has doubled in size as it adds new customers and expands the development of its Skylink platform. Skylink leads the charge to move WebRTC, traditionally seen as a desktop, browser based technology, to become a ubiquitous web communications technology on web and mobile, as well as Internet of Things compatible devices.
SYS-CON Events announced today that AIC, a leading provider of OEM/ODM server and storage solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. AIC is a leading provider of both standard OTS, off-the-shelf, and OEM/ODM server and storage solutions. With expert in-house design capabilities, validation, manufacturing and production, AIC's broad selection of products are highly flexible and are configurable to any form factor or custom configuration. AIC leads the industry with nearly 20 years of ...
“With easy-to-use SDKs for Atmel’s platforms, IoT developers can now reap the benefits of realtime communication, and bypass the security pitfalls and configuration complexities that put IoT deployments at risk,” said Todd Greene, founder & CEO of PubNub. PubNub will team with Atmel at CES 2015 to launch full SDK support for Atmel’s MCU, MPU, and Wireless SoC platforms. Atmel developers now have access to PubNub’s secure Publish/Subscribe messaging with guaranteed ¼ second latencies across PubNub’s 14 global points-of-presence. PubNub delivers secure communication through firewalls, proxy ser...
SYS-CON Events announced today that Vicom Computer Services, Inc., a provider of technology and service solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. They are located at booth #427. Vicom Computer Services, Inc. is a progressive leader in the technology industry for over 30 years. Headquartered in the NY Metropolitan area. Vicom provides products and services based on today’s requirements around Unified Networks, Cloud Computing strategies, Virtualization around Software defined Data Ce...
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Chuck Piluso will present a study of cloud adoption trends and the power and flexibility of IBM Power and Pureflex cloud solutions. Speaker Bio: Prior to Data Storage Corporation (DSC), Mr. Piluso founded North American Telecommunication Corporation, a facilities-based Competitive Local Exchange Carrier licensed by the Public Service Commission in 10 states, serving as the company's chairman and president from 1997 to 2000. Between 1990 and 1997, Mr. Piluso served as chairman & founder of International Telecommunications Corporation, a facilities-based international carrier licensed by t...
There are lots of challenges in IoT around secure, scalable and business friendly infrastructure for enterprises. For large corporations, IoT implementations are one of the top priorities of the decade. All industries are seeing a competitive need to sustain by investing in IoT initiatives. The value addition comes from improved customer service, innovative product and additional revenue streams. The data from these IP-connected devices can be leveraged for a variety of business applications as well as responsive action controls. The various architectural building blocks of an IoT ...
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
SYS-CON Events announced today that Ciqada will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Ciqada™ makes it easy to connect your products to the Internet. By integrating key components - hardware, servers, dashboards, and mobile apps - into an easy-to-use, configurable system, your products can quickly and securely join the internet of things. With remote monitoring, control, and alert messaging capability, you will meet your customers' needs of tomorrow - today! Ciqada. Let your products take flight. For more inform...
WebRTC is an up-and-coming standard that enables real-time voice and video to be directly embedded into browsers making the browser a primary user interface for communications and collaboration. WebRTC runs in a number of browsers today and is currently supported in over a billion installed browsers globally, across a range of platform OS and devices. Today, organizations that choose to deploy WebRTC applications and use a host machine that supports audio through USB or Bluetooth can use Plantronics products to connect and transit or receive the audio associated with the WebRTC session.
The best mobile applications are augmented by dedicated servers, the Internet and Cloud services. Mobile developers should focus on one thing: writing the next socially disruptive viral app. Thanks to the cloud, they can focus on the overall solution, not the underlying plumbing. From iOS to Android and Windows, developers can leverage cloud services to create a common cross-platform backend to persist user settings, app data, broadcast notifications, run jobs, etc. This session provides a high level technical overview of many cloud services available to mobile app developers, includi...
Health care systems across the globe are under enormous strain, as facilities reach capacity and costs continue to rise. M2M and the Internet of Things have the potential to transform the industry through connected health solutions that can make care more efficient while reducing costs. In fact, Vodafone's annual M2M Barometer Report forecasts M2M applications rising to 57 percent in health care and life sciences by 2016. Lively is one of Vodafone's health care partners, whose solutions enable older adults to live independent lives while staying connected to loved ones. M2M will continue to gr...
Dave will share his insights on how Internet of Things for Enterprises are transforming and making more productive and efficient operations and maintenance (O&M) procedures in the cleantech industry and beyond. Speaker Bio: Dave Landa is chief operating officer of Cybozu Corp (kintone US). Based in the San Francisco Bay Area, Dave has been on the forefront of the Cloud revolution driving strategic business development on the executive teams of multiple leading Software as a Services (SaaS) application providers dating back to 2004. Cybozu's kintone.com is a leading global BYOA (Build Your O...
As enterprises move to all-IP networks and cloud-based applications, communications service providers (CSPs) – facing increased competition from over-the-top providers delivering content via the Internet and independently of CSPs – must be able to offer seamless cloud-based communication and collaboration solutions that can scale for small, midsize, and large enterprises, as well as public sector organizations, in order to keep and grow market share. The latest version of Oracle Communications Unified Communications Suite gives CSPs the capability to do just that. In addition, its integration ...
The IoT Bootcamp is coming to Cloud Expo | @ThingsExpo on June 9-10 at the Javits Center in New York. Instructor. Registration is now available at http://iotbootcamp.sys-con.com/ Instructor Janakiram MSV previously taught the famously successful Multi-Cloud Bootcamp at Cloud Expo | @ThingsExpo in November in Santa Clara. Now he is expanding the focus to Janakiram is the founder and CTO of Get Cloud Ready Consulting, a niche Cloud Migration and Cloud Operations firm that recently got acquired by Aditi Technologies. He is a Microsoft Regional Director for Hyderabad, India, and one of the f...
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal today!
While not quite mainstream yet, WebRTC is starting to gain ground with Carriers, Enterprises and Independent Software Vendors (ISV’s) alike. WebRTC makes it easy for developers to add audio and video communications into their applications by using Web browsers as their platform. But like any market, every customer engagement has unique requirements, as well as constraints. And of course, one size does not fit all. In her session at WebRTC Summit, Dr. Natasha Tamaskar, Vice President, Head of Cloud and Mobile Strategy at GENBAND, will explore what is needed to take a real time communications ...