Welcome!

Open Source Cloud Authors: William Schmarzo, Karthick Viswanathan, Elizabeth White, Derek Weeks, Progress Blog

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.

Prerequisites
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
Consumers increasingly expect their electronic "things" to be connected to smart phones, tablets and the Internet. When that thing happens to be a medical device, the risks and benefits of connectivity must be carefully weighed. Once the decision is made that connecting the device is beneficial, medical device manufacturers must design their products to maintain patient safety and prevent compromised personal health information in the face of cybersecurity threats. In his session at @ThingsExpo...
SYS-CON Events announced today that Massive Networks will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Massive Networks mission is simple. To help your business operate seamlessly with fast, reliable, and secure internet and network solutions. Improve your customer's experience with outstanding connections to your cloud.
The question before companies today is not whether to become intelligent, it’s a question of how and how fast. The key is to adopt and deploy an intelligent application strategy while simultaneously preparing to scale that intelligence. In her session at 21st Cloud Expo, Sangeeta Chakraborty, Chief Customer Officer at Ayasdi, will provide a tactical framework to become a truly intelligent enterprise, including how to identify the right applications for AI, how to build a Center of Excellence to ...
From 2013, NTT Communications has been providing cPaaS service, SkyWay. Its customer’s expectations for leveraging WebRTC technology are not only typical real-time communication use cases such as Web conference, remote education, but also IoT use cases such as remote camera monitoring, smart-glass, and robotic. Because of this, NTT Communications has numerous IoT business use-cases that its customers are developing on top of PaaS. WebRTC will lead IoT businesses to be more innovative and address...
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution and join Akvelon expert and IoT industry leader, Sergey Grebnov, in his session at @ThingsExpo, for an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
Because IoT devices are deployed in mission-critical environments more than ever before, it’s increasingly imperative they be truly smart. IoT sensors simply stockpiling data isn’t useful. IoT must be artificially and naturally intelligent in order to provide more value In his session at @ThingsExpo, John Crupi, Vice President and Engineering System Architect at Greenwave Systems, will discuss how IoT artificial intelligence (AI) can be carried out via edge analytics and machine learning techn...
WebRTC is the future of browser-to-browser communications, and continues to make inroads into the traditional, difficult, plug-in web communications world. The 6th WebRTC Summit continues our tradition of delivering the latest and greatest presentations within the world of WebRTC. Topics include voice calling, video chat, P2P file sharing, and use cases that have already leveraged the power and convenience of WebRTC.
SYS-CON Events announced today that GrapeUp, the leading provider of rapid product development at the speed of business, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Grape Up is a software company, specialized in cloud native application development and professional services related to Cloud Foundry PaaS. With five expert teams that operate in various sectors of the market acr...
SYS-CON Events announced today that Datera, that offers a radically new data management architecture, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datera is transforming the traditional datacenter model through modern cloud simplicity. The technology industry is at another major inflection point. The rise of mobile, the Internet of Things, data storage and Big...
In his opening keynote at 20th Cloud Expo, Michael Maximilien, Research Scientist, Architect, and Engineer at IBM, discussed the full potential of the cloud and social data requires artificial intelligence. By mixing Cloud Foundry and the rich set of Watson services, IBM's Bluemix is the best cloud operating system for enterprises today, providing rapid development and deployment of applications that can take advantage of the rich catalog of Watson services to help drive insights from the vast t...
SYS-CON Events announced today that CA Technologies has been named "Platinum Sponsor" of SYS-CON's 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business - from apparel to energy - is being rewritten by software. From planning to development to management to security, CA creates software that fuels transformation for companies in the applic...
Recently, IoT seems emerging as a solution vehicle for data analytics on real-world scenarios from setting a room temperature setting to predicting a component failure of an aircraft. Compared with developing an application or deploying a cloud service, is an IoT solution unique? If so, how? How does a typical IoT solution architecture consist? And what are the essential components and how are they relevant to each other? How does the security play out? What are the best practices in formulating...
In his session at @ThingsExpo, Arvind Radhakrishnen discussed how IoT offers new business models in banking and financial services organizations with the capability to revolutionize products, payments, channels, business processes and asset management built on strong architectural foundation. The following topics were covered: How IoT stands to impact various business parameters including customer experience, cost and risk management within BFS organizations.
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
SYS-CON Events announced today that Elastifile will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Elastifile Cloud File System (ECFS) is software-defined data infrastructure designed for seamless and efficient management of dynamic workloads across heterogeneous environments. Elastifile provides the architecture needed to optimize your hybrid cloud environment, by facilitating efficient...
There is only one world-class Cloud event on earth, and that is Cloud Expo – which returns to Silicon Valley for the 21st Cloud Expo at the Santa Clara Convention Center, October 31 - November 2, 2017. Every Global 2000 enterprise in the world is now integrating cloud computing in some form into its IT development and operations. Midsize and small businesses are also migrating to the cloud in increasing numbers. Companies are each developing their unique mix of cloud technologies and service...
SYS-CON Events announced today that Golden Gate University will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Since 1901, non-profit Golden Gate University (GGU) has been helping adults achieve their professional goals by providing high quality, practice-based undergraduate and graduate educational programs in law, taxation, business and related professions. Many of its courses are taug...
SYS-CON Events announced today that Grape Up will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct. 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Grape Up is a software company specializing in cloud native application development and professional services related to Cloud Foundry PaaS. With five expert teams that operate in various sectors of the market across the U.S. and Europe, Grape Up works with a variety of customers from emergi...
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
21st International Cloud Expo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Me...