Open Source Cloud Authors: Liz McMillan, Elizabeth White, Flint Brenton, Jason Bloomberg, Yeshim Deniz

Related Topics: Open Source Cloud

Open Source Cloud: Article

Multi-Core Debugging and Performance Enhancement

Additional pressures on complex applications

Computer systems have fully entered the age of multi-core processing. This trend was examined in a white paper entitled, "Preparing for the Revolution, Maximizing Dual-Core Technology." While much of the focus had been on dual-core processors, Intel has now delivered quad-core processors and AMD has announced quad-core availability in 2007. Software developers who are just taking advantage of multiple processors also need to be looking ahead since even larger multi-core platforms will reach the market soon. This new technology puts additional pressures on complex applications. In essence, the push beyond dual-cores has made the choice of development tools a key factor for successful projects.

When writing multi-core software, there are two important issues facing software developers. The first and most familiar is correctness of the program, i.e., does the program work properly and get the right answer. While this seems obvious, in multi-core applications, incorrect program behavior can arise from several sources not present in single-core design.

The second important feature is program performance. An assumption that speed-up is automatic just because a program has been modified to utilize multi-cores can be a huge mistake. Improved performance is not necessarily automatic or guaranteed.

With the introduction of quad-core processors, applications have the option of using eight cores on one dual-socket motherboard. Proper use of these additional resources will be critical to software development. This article will provide some insight into these issues and present some solutions to the problems facing multi-core programmers using the Linux operating system.

As suggested in the white paper mentioned above, some consideration should be given to the method of parallelization. Two basic models are available to programmers - program threads and message passing. While message passing is the predominant method used in High Performance Computing (HPC), threads are becoming more important as both the core and socket sizes increase in most new motherboards.

Given that message passing programming is covered by other sources, this article will focus on threaded programming on multi-core processors using Linux.

A general approach to parallel computing is first to take a working sequential program, a program that is known to operate correctly on one CPU, and use it as the basis for a parallel program. This technique has two big advantages. First, the program can be tested to ensure that it operates at an acceptable level of correctness. (i.e., the program works and any issues are known in advance). Second, the programmer has a performance baseline with which to measure the new multi-core program.

If a new program is being written, it's highly advisable to create and debug a sequential version first. Adding the additional complexity of parallel programming to standard software development makes isolating bugs and problems more difficult.

In general, threaded programs often have multiple independent parts that share the same data set. One way to use threaded programming is to allow subroutines to operate independently and at the same time. It's also possible to break large loops up into threads as well. In all cases, however, a good design will allow the threaded version to "collapse" into a single thread by setting a thread count variable to one.

Finally, since there are adequate resources for learning about threaded programming, we'll concentrate on ways to ensure correct program operation and optimal performance.

Programming with Threads
The thread model is a way for a program to split itself into two or more concurrent tasks. These tasks can be run on a single processor in a time-shared mode, or on separate processors (e.g., the two cores on a dual-core processor can each run threads). The term thread comes from "thread of execution" and is a reference to how a fabric (computer program) can be pulled apart into threads (concurrent parts). Threads are different from individual processes (or independent programs), because they inherit much of their state information and memory from the parent process. Threads provide the ability to share memory and offer very fine-grained synchronization with other sibling threads.

On Linux and Unix systems threads are often implemented using a POSIX Thread Library (pthreads). There are several other thread models (Windows threads) from which the programmer can choose, however, using a standards-based implementation like POSIX is highly recommended. As a low-level library, pthreads can be easily included in almost all programming applications. This article will discuss debugging and optimizing Linux threads.

Ensuring Program Correctness
Of course, all programmers know that just because a program finishes, it doesn't mean the answers are correct. With multi-core programming, this situation may manifest itself differently. The same program and data, run at different times, may produce different answers, or cease functioning altogether for no apparent reason. We'll explore some of these causes and present some solutions.

Deadlock and Livelock
Because individual threads share memory and I/O, there must be a way for each thread to protect memory segments and I/O resources while they're using it. To solve this problem, threaded code employs "locks" that provide the thread exclusive access to a resource.

While the introduction of locks provides a solution to this problem, it also creates the possibility of a deadlock occurring in the program. Consider the following scenario where there are two global variables called Total and Sub-Total.

Process 1 locks the variable Total
Process 2 locks the variable Sub-Total
Process 1 attempts to acquire a lock on Sub-Total
Process 2 attempts to acquire a lock on Total

The program is now in a deadlock situation. Deadlock may develop every time the program runs or it may happen randomly when the timing is right. There's also a condition called "livelock" that's similar to deadlock. Livelock results when a thread or threads are constantly trying to acquire a lock, but can't because it's being used by another part of the program (or more likely hasn't been unlocked properly). Livelock may stop certain threads, but not necessarily cause the whole program to stop. With livelock, a program may appear to be working, but in reality it's often stuck in a loop, which can make it hard to determine the exact cause of the problem.

While deadlock and livelock can often be recognized through program behavior (i.e., the program stops, crashes, or gets stuck in one place), locating the cause can be difficult at times unless you can look at the threads in real-time. Certain lock conditions have a temporal component and can be hard to reproduce unless the program is running in production mode (i.e., a specific sequence or timing of events caused the situation).

More Stories By Douglas Eadline

Dr. Douglas Eadline has over 25 years of experience in high-performance computing. You can contact him through Basement Supercomputing (http://basement-supercomputing.com).

More Stories By Vince Hauber

Vince Hauber, a senior product manager with Concurrent Computer Corporation, has over 40 years experience in system software and platform solutions. Concurrent is a leading provider of real-time Linux distributions and tools.

Comments (0)

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.

@ThingsExpo Stories
DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
DXWorldEXPO LLC announced today that "Miami Blockchain Event by FinTechEXPO" has announced that its Call for Papers is now open. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Financial enterprises in New York City, London, Singapore, and other world financial capitals are embracing a new generation of smart, automated FinTech that eliminates many cumbersome, slow, and expe...
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
DevOpsSummit New York 2018, colocated with CloudEXPO | DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City. Digital Transformation (DX) is a major focus with the introduction of DXWorldEXPO within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of bus...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
As IoT continues to increase momentum, so does the associated risk. Secure Device Lifecycle Management (DLM) is ranked as one of the most important technology areas of IoT. Driving this trend is the realization that secure support for IoT devices provides companies the ability to deliver high-quality, reliable, secure offerings faster, create new revenue streams, and reduce support costs, all while building a competitive advantage in their markets. In this session, we will use customer use cases...
DXWorldEXPO LLC announced today that ICOHOLDER named "Media Sponsor" of Miami Blockchain Event by FinTechEXPO. ICOHOLDER give you detailed information and help the community to invest in the trusty projects. Miami Blockchain Event by FinTechEXPO has opened its Call for Papers. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Miami Blockchain Event by FinTechEXPO also offers s...
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities - ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups.
Internet-of-Things discussions can end up either going down the consumer gadget rabbit hole or focused on the sort of data logging that industrial manufacturers have been doing forever. However, in fact, companies today are already using IoT data both to optimize their operational technology and to improve the experience of customer interactions in novel ways. In his session at @ThingsExpo, Gordon Haff, Red Hat Technology Evangelist, shared examples from a wide range of industries – including en...
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Rodrigo Coutinho is part of OutSystems' founders' team and currently the Head of Product Design. He provides a cross-functional role where he supports Product Management in defining the positioning and direction of the Agile Platform, while at the same time promoting model-based development and new techniques to deliver applications in the cloud.
Predicting the future has never been more challenging - not because of the lack of data but because of the flood of ungoverned and risk laden information. Microsoft states that 2.5 exabytes of data are created every day. Expectations and reliance on data are being pushed to the limits, as demands around hybrid options continue to grow.
Business professionals no longer wonder if they'll migrate to the cloud; it's now a matter of when. The cloud environment has proved to be a major force in transitioning to an agile business model that enables quick decisions and fast implementation that solidify customer relationships. And when the cloud is combined with the power of cognitive computing, it drives innovation and transformation that achieves astounding competitive advantage.
Poor data quality and analytics drive down business value. In fact, Gartner estimated that the average financial impact of poor data quality on organizations is $9.7 million per year. But bad data is much more than a cost center. By eroding trust in information, analytics and the business decisions based on these, it is a serious impediment to digital transformation.