OpenACC Starts to Gather Developer Mindshare

By Michael Feldman

May 17, 2012

PGI, Cray, and CAPS enterprise are moving quickly to get their new OpenACC-supported compilers into the hands of GPGPU developers. At NVIDIA’s GPU Technology Conference (GTC) this week, there was plenty of discussion around the new HPC accelerator framework, and all three OpenACC compiler makers, as well as NVIDIA, were talking up the technology.

Announced at the Supercomputing Conference (SC11) last November, OpenACC is an open standard API developed by NVIDIA, PGI, Cray, and CAPS, to provide a high-level programming framework for programming accelerators like GPUs. OpenACC uses compiler directives, which programmers insert into high-level source (e.g., C, C++ or Fortran), to tell the compiler to execute specific pieces of the code on the accelerator hardware.

GTC conference-goers had plenty of opportunity to encounter OpenACC this week. There two OpenACC tutorials for would-be developers, one by NVIDIA, and the other by CAPS enterprise. In addition, there were four other sessions hosted by Cray, CAPS, and PGI throughout the week. That’s not counting the numerous mentions OpenACC got during other presentations involving GPGPU programming.

The technology is still in its infancy though. The PGI and Cray compilers are pre-production versions. CAPS first commercial offering is just two weeks old.

The initial goal of OpenACC is to bring more developers (and codes) into GPU computing, especially those not being served by the lower-level programming frameworks like CUDA and OpenCL. While CUDA is widely used in universities and in the technical computing realm, and OpenCL is emerging as an open standard for parallel computing, neither is particular attractive to commercial developers.

Most programmers are used to writing high-level code that focuses on the problem at hand, without have to worry about the vagaries of the underlying hardware. That hardware independence is also what makes OpenACC attractive for codes that need to span different processor architectures.

That assumes, of course, that compiler will support multiple accelerator chips. The first crop of OpenACC-enabled compilers from PGI, CAPS and Cray only generate code for NVIDIA GPUs — not too surprising when you consider NVIDIA’s current dominance in HPC acceleration. However all of the compiler efforts plan to widen the aperture of hardware support.

CAPS is perhaps most aggressive in this regard. According to CAPS CTO François Bodin, his company plans to add OpenACC support for AMD GPUs, x86 multicore CPUs and even the Tegra 3 microprocessor, an ARM-GPU design that will be used to power an experimental HPC clusters at the Barcelona Supercomputing Center (BSC). Bodin also said that they have an Intel MIC (Many Integrated Core) port of OpenACC in the pipeline. All of these compiler ports should be available later this year.

PGI is keeping its OpenACC development plans a little closer to the vest. But according to PGI compiler engineer Michael Wolfe, they have received requests for OpenACC support for nearly every processor and co-processor used in high performance computing. The compiler maker will undoubtedly be developing some of these over the next year.

Likewise for Cray, although its OpenACC compiler support is focused on the underlying accelerators of its own XK6 supercomputers. At this point, that’s confined to NVIDIA GPUs. Cray (which also carries CAPS and PGI compilers for its customers) has a unique OpenACC offering in that it supports those directives in PGAS languages Co-Array Fortran and Unified Parallel C (UPC) on the XK6.

Besides its applicability to multiple hardware platforms, OpenACC is just plain easier to use when you have lots of existing code. For one thing, OpenACC lets you attack the acceleration in steps. CUDA and OpenCL ports usually require code rewrites of at least a sizeable chunk of the application being accelerated, using low-level APIs. With OpenACC, the programmer just has to insert high-level directives into existing source, and this can be done iteratively, gradually putting more and more of the code under OpenACC control. This, say, PGI’s Wolfe, is “a hell of a lot more productive” than the low-level approach.

Even at the national labs and research centers, where there are computer scientists aplenty, OpenACC is starting to be recognized as an easier path to bring acceleration to hundreds of thousands of line of legacy codes. NASA Ames is already using PGI’s compiler to speed up some of their CFD codes on one of their GPU clusters. And the upcoming deployments of multi-petaflop GPU-based supercomputers like “Titan” at Oak Ridge National Lab, should provide a lot more opportunities for OpenACC-based application development. Titan project director Buddy Bland is on record endorsing the technology for software development on that machine.

As with all parallel programming though, there’s no free lunch to be had. In general, the programmer is probably going to sacrifice some runtime performance (compared to CUDA, for example) for the sake of programmer productivity. But there seems to be a general consensus that intelligent use of directives can easily get you to within 10 or 15 percent the performance of a low-level implementation. But as CAPS’ Bodin explains, to get in that close, “you have to know what you’re doing.” On the other hand, as the compiler technology matures and developers get more adept with OpenACC, the performance gap could narrow even further.

The other problem is just a lack of accelerator diversity at the moment. With Intel MIC waiting in the wings, and AMD still pretty much a no-show with server-side GPUs, there’s no immediate need to support anything but NVIDIA’s GPU architecture right now. Worse, both Intel and AMD are backing other parallel computing frameworks that they are rolling into to their accelerator programs: OpenMP, Cilk Plus, and TBB for Intel; OpenCL and C++ AMP for AMD.

Fortunately, it probably doesn’t matter that Intel and AMD haven’t hopped on the OpenACC bandwagon. PGI and CAPS can still produce compilers targeting Intel MIC or AMD GPUs, or whatever else comes along. And as long as there are at least two compiler vendors offering such support, the community should be satisfied.

The end game, though, is to fold the OpenACC capabilities into OpenMP. If and when that happens, both Intel, AMD will throw their support behind it. OpenMP has been around for 15 years and is a true industry standard.

There is currently a Working Group on Accelerators in the OpenMP consortium, which is looking at incorporating accelerator directives into the next OpenMP release. And while those directives will be based on the OpenACC directives, they are not likely to be adopted as is. There’s a real risk that if the process gets drawn out much longer and OpenACC captures a critical mass of users, there will end up being two directive-based accelerator standards to choose from.

Twas ever thus.

Related Articles

CAPS Entreprise Now Supports OpenACC Standard

OpenMP Announces Improvements for Multicore and Accelerators

OpenACC Support Available With New PGI Accelerator Fortran and C Compilers

NVIDIA Announces Initial Results of Directives-Based GPU Computing Program

NVIDIA Eyes Post-CUDA Era of GPU Computing

Subscribe to HPCwire's Weekly Update!

Be the most informed person in the room! Stay ahead of the tech trends with industy updates delivered to you every week!

Insights from Optimized Codes on Cineca’s Marconi

February 15, 2019

What can you do with 381,392 CPU cores? For Cineca, it means enabling computational scientists to expand a large part of the world’s body of knowledge from the nanoscale to the astronomic, from calculating quantum effe Read more…

By Ken Strandberg

What Will IBM’s AI Debater Learn from Its Loss?

February 14, 2019

The utility of IBM’s latest man-versus-machine gambit is debatable. At the very least its Project Debater got us thinking about the potential uses of artificial intelligence as a way of helping humans sift through al Read more…

By George Leopold

ClusterVision in Bankruptcy, Fate Uncertain

February 13, 2019

ClusterVision, European HPC specialists that have built and installed over 20 Top500-ranked systems in their nearly 17-year history, appear to be in the midst of bankruptcy proceedings. According to Dutch news site Drimb Read more…

By Tiffany Trader

HPE Extreme Performance Solutions

HPE Systems With Intel Omni-Path: Architected for Value and Accessible High-Performance Computing

Today’s high-performance computing (HPC) and artificial intelligence (AI) users value high performing clusters. And the higher the performance that their system can deliver, the better. Read more…

IBM Accelerated Insights

Medical Research Powered by Data

“We’re all the same, but we’re unique as well. In that uniqueness lies all of the answers….”

  • Mark Tykocinski, MD, Provost, Executive Vice President for Academic Affairs, Thomas Jefferson University

Getting the answers to what causes some people to develop diseases and not others is driving the groundbreaking medical research being conducted by the Computational Medicine Center at Thomas Jefferson University in Philadelphia. Read more…

South African Weather Service Doubles Compute and Triples Storage Capacity of Cray System

February 13, 2019

South Africa has made headlines in recent years for its commitment to HPC leadership in Africa – and now, Cray has announced another major South African HPC expansion. Cray has been awarded contracts with Eclipse Holdings Ltd. to upgrade the supercomputing system operated by the South African Weather Service (SAWS). Read more…

By Oliver Peckham

Insights from Optimized Codes on Cineca’s Marconi

February 15, 2019

What can you do with 381,392 CPU cores? For Cineca, it means enabling computational scientists to expand a large part of the world’s body of knowledge from th Read more…

By Ken Strandberg

ClusterVision in Bankruptcy, Fate Uncertain

February 13, 2019

ClusterVision, European HPC specialists that have built and installed over 20 Top500-ranked systems in their nearly 17-year history, appear to be in the midst o Read more…

By Tiffany Trader

UC Berkeley Paper Heralds Rise of Serverless Computing in the Cloud – Do You Agree?

February 13, 2019

Almost exactly ten years to the day from publishing of their widely-read, seminal paper on cloud computing, UC Berkeley researchers have issued another ambitious examination of cloud computing - Cloud Programming Simplified: A Berkeley View on Serverless Computing. The new work heralds the rise of ‘serverless computing’ as the next dominant phase of cloud computing. Read more…

By John Russell

Iowa ‘Grows Its Own’ to Fill the HPC Workforce Pipeline

February 13, 2019

The global workforce that supports advanced computing, scientific software and high-speed research networks is relatively small when you stop to consider the magnitude of the transformative discoveries it empowers. Technical conferences provide a forum where specialists convene to learn about the latest innovations and schedule face-time with colleagues from other institutions. Read more…

By Elizabeth Leake, STEM-Trek

Trump Signs Executive Order Launching U.S. AI Initiative

February 11, 2019

U.S. President Donald Trump issued an Executive Order (EO) today launching a U.S Artificial Intelligence Initiative. The new initiative - Maintaining American L Read more…

By John Russell

Celebrating Women in Science: Meet Four Women Leading the Way in HPC

February 11, 2019

One only needs to look around at virtually any CS/tech conference to realize that women are underrepresented, and that holds true of HPC. SC hosts over 13,000 H Read more…

By AJ Lauer

IBM Bets $2B Seeking 1000X AI Hardware Performance Boost

February 7, 2019

For now, AI systems are mostly machine learning-based and “narrow” – powerful as they are by today's standards, they're limited to performing a few, narro Read more…

By Doug Black

Assessing Government Shutdown’s Impact on HPC

February 6, 2019

After a 35-day federal government shutdown, the longest in U.S. history, government agencies are taking stock of the damage -- and girding for a potential secon Read more…

By Tiffany Trader

Quantum Computing Will Never Work

November 27, 2018

Amid the gush of money and enthusiastic predictions being thrown at quantum computing comes a proposed cold shower in the form of an essay by physicist Mikhail Read more…

By John Russell

Cray Unveils Shasta, Lands NERSC-9 Contract

October 30, 2018

Cray revealed today the details of its next-gen supercomputing architecture, Shasta, selected to be the next flagship system at NERSC. We've known of the code-name "Shasta" since the Argonne slice of the CORAL project was announced in 2015 and although the details of that plan have changed considerably, Cray didn't slow down its timeline for Shasta. Read more…

By Tiffany Trader

The Case Against ‘The Case Against Quantum Computing’

January 9, 2019

It’s not easy to be a physicist. Richard Feynman (basically the Jimi Hendrix of physicists) once said: “The first principle is that you must not fool yourse Read more…

By Ben Criger

AMD Sets Up for Epyc Epoch

November 16, 2018

It’s been a good two weeks, AMD’s Gary Silcott and Andy Parma told me on the last day of SC18 in Dallas at the restaurant where we met to discuss their show news and recent successes. Heck, it’s been a good year. Read more…

By Tiffany Trader

Intel Reportedly in $6B Bid for Mellanox

January 30, 2019

The latest rumors and reports around an acquisition of Mellanox focus on Intel, which has reportedly offered a $6 billion bid for the high performance interconn Read more…

By Doug Black

US Leads Supercomputing with #1, #2 Systems & Petascale Arm

November 12, 2018

The 31st Supercomputing Conference (SC) - commemorating 30 years since the first Supercomputing in 1988 - kicked off in Dallas yesterday, taking over the Kay Ba Read more…

By Tiffany Trader

Looking for Light Reading? NSF-backed ‘Comic Books’ Tackle Quantum Computing

January 28, 2019

Still baffled by quantum computing? How about turning to comic books (graphic novels for the well-read among you) for some clarity and a little humor on QC. The Read more…

By John Russell

Contract Signed for New Finnish Supercomputer

December 13, 2018

After the official contract signing yesterday, configuration details were made public for the new BullSequana system that the Finnish IT Center for Science (CSC Read more…

By Tiffany Trader

Leading Solution Providers

SC 18 Virtual Booth Video Tour

Advania @ SC18 AMD @ SC18
ASRock Rack @ SC18
DDN Storage @ SC18
HPE @ SC18
IBM @ SC18
Lenovo @ SC18 Mellanox Technologies @ SC18
NVIDIA @ SC18
One Stop Systems @ SC18
Oracle @ SC18 Panasas @ SC18
Supermicro @ SC18 SUSE @ SC18 TYAN @ SC18
Verne Global @ SC18

Deep500: ETH Researchers Introduce New Deep Learning Benchmark for HPC

February 5, 2019

ETH researchers have developed a new deep learning benchmarking environment – Deep500 – they say is “the first distributed and reproducible benchmarking s Read more…

By John Russell

ClusterVision in Bankruptcy, Fate Uncertain

February 13, 2019

ClusterVision, European HPC specialists that have built and installed over 20 Top500-ranked systems in their nearly 17-year history, appear to be in the midst o Read more…

By Tiffany Trader

IBM Quantum Update: Q System One Launch, New Collaborators, and QC Center Plans

January 10, 2019

IBM made three significant quantum computing announcements at CES this week. One was introduction of IBM Q System One; it’s really the integration of IBM’s Read more…

By John Russell

Nvidia’s Jensen Huang Delivers Vision for the New HPC

November 14, 2018

For nearly two hours on Monday at SC18, Jensen Huang, CEO of Nvidia, presented his expansive view of the future of HPC (and computing in general) as only he can do. Animated. Backstopped by a stream of data charts, product photos, and even a beautiful image of supernovae... Read more…

By John Russell

HPC Reflections and (Mostly Hopeful) Predictions

December 19, 2018

So much ‘spaghetti’ gets tossed on walls by the technology community (vendors and researchers) to see what sticks that it is often difficult to peer through Read more…

By John Russell

IBM Bets $2B Seeking 1000X AI Hardware Performance Boost

February 7, 2019

For now, AI systems are mostly machine learning-based and “narrow” – powerful as they are by today's standards, they're limited to performing a few, narro Read more…

By Doug Black

The Deep500 – Researchers Tackle an HPC Benchmark for Deep Learning

January 7, 2019

How do you know if an HPC system, particularly a larger-scale system, is well-suited for deep learning workloads? Today, that’s not an easy question to answer Read more…

By John Russell

Intel Confirms 48-Core Cascade Lake-AP for 2019

November 4, 2018

As part of the run-up to SC18, taking place in Dallas next week (Nov. 11-16), Intel is doling out info on its next-gen Cascade Lake family of Xeon processors, specifically the “Advanced Processor” version (Cascade Lake-AP), architected for high-performance computing, artificial intelligence and infrastructure-as-a-service workloads. Read more…

By Tiffany Trader

  • arrow
  • Click Here for More Headlines
  • arrow
Do NOT follow this link or you will be banned from the site!
Share This