During SC14, Michael Klemm from Intel and myself teamed up to give an OpenMP 4.0 overview talk at the OpenMP booth. Our goal was to touch on all important aspects, from thread binding over tasking to accelerator support, and to entertain our audience in doing so. Although not all jokes translate from German to English as we intended, I absolutely think that the resulting video is a fun-oriented 25-minutes run-down of OpenMP 4.0 and worth sharing here:
Since 2001 already, the IT Center (formerly: Center for Computing and Communication) of RWTH Aachen University offers a one week HPC workshop on Parallel Programming during spring time. This course is not restricted to scientists and engineers from our university, in fact we have about 30% of external attendees each time. This year we were very happy about a record attendance of up to 85 persons for the OpenMP lectures on Wednesday. As usual we publish all course materials online, but this year we also created screencasts from all presentations. That means you see the slides and the live demos and you hear the presenter talk. This blog post contains links to both the screencasts as well as the other course material, sorted by topic.
We have three talks as an introduction to OpenMP from Wednesday and two talks on selected topics from Thursday, which were vectorization and tools.
Introduction to OpenMP Programming (part 1), by Christian Terboven:
Getting OpenMP up to Speed, by Ruud van der Pas:
Introduction to OpenMP Programming (part 2), by Christian Terboven:
Vectorization with OpenMP, by Dirk Schmidl:
Tools for OpenMP Programming, by Dirk Schmidl:
We have two talks as an introduction to MPI and one on using the Vampir toolchain, all from Tuesday.
Introduction to MPI Programming (part 1), by Hristo Iliev:
Introduction to MPI Programming (part 2), by Hristo Iliev:
Introduction to VampirTrace and Vampir by Hristo Iliev:
Intel Xeon Phi
We put a special focus on presenting this architecture and we have one overview talk and one talk on using OpenMP 4.0 constructs for this architecture.
Programming the Intel Xeon Phi Coprocessor Overview, by Tim Cramer:
OpenMP 4.0 for Accelerators, by Christian Terboven:
Some more talks, for instance on using our cluster or basics of parallel computer architectures, can be found in the youtube channel: https://www.youtube.com/channel/UCtdrEoe46tD2IvJJRs_JH1A.
A while ago I published a list with articles and tutorials on OpenMP 4.0, including the German article on heise Developer I wrote together with Michael Klemm (Intel). A slightly modified English version of our text now appeared in issue 16 of Intel’s Parallel Universe magazine, titled Full throttle: OpenMP 4.0.
The current issue and also past issues of the Parallel Universe magazine are available at http://software.intel.com/en-us/intel-parallel-universe-magazine. If you are interested in developing parallel code for Intel architectures you might find some interesting reads over there.
Quoting from openmp.org: OpenMP, the de-facto standard for parallel programming on shared memory systems, continues to extend its reach beyond pure HPC to include embedded systems, real time systems, and accelerators. Release Candidate 1 of the OpenMP 4.0 API specifications currently under development is now available for public discussion. This update includes thread affinity, initial support for Fortran 2003, SIMD constructs to vectorize both serial and parallelized loops, user-defined reductions, and sequentially consistent atomics. The OpenMP ARB plans to integrate the Technical Report on directives for attached accelerators, as well as more new features, in a final Release Candidate 2, to appear sometime in the first Quarter of 2013, followed by the finalized full 4.0 API specifications soon thereafter.
The OpenMP Language Commmittee really put a lot of effort and dedicated work into both documents and we hope for good, constructive feedback. Both documents are available at the OpenMP Specifications webpage: http://openmp.org/wp/openmp-specifications/.
Grab them now while they are hot :-).
Expect big news on OpenMP 4.0 for next week’s SC12. The OpenMP Language Committee – responsible for developing the standard – always planned to release the next version of the standard as a draft for public comment in time for SC12. We worked very hard during the last weeks to stay within our schedule. And we will do the following:
- Release OpenMP 4.0 RC1 as a draft for public review. This document will be in a pretty good shape and will represent the foundation of OpenMP 4.0. It will contain several new features, to be discussed and explained during SC12 at our booth and/or the OpenMP BoF. Among these new features is the SIMD construct, to vectorize both serial as well as parallelized loops, taskgroups (no task dependencies yet), thread binding via places (I talked a lot on this already), array sectioning, basic support for Fortran 2003, and some other minor corrections and improvements.
- Publish a Technical Report on OpenMP for Accelerators, more specifically on “Directives for Attached Accelerators”. This was always planned to be the major addition for OpenMP 4.0. However, integrating support for accelerators with the rest of OpenMP is a hard task and a lot of work, and it is not 100% done yet. There were many discussion on how to deal with this situation: do as outlined here, wait for just some more weeks, come up with a completely new schedule and wait until we are completely done, … . Almost all technical aspects have been discussed and answered. But the wording is not yet completed. And support for NVIDIA-like GPUs might not be optimal. However, I personally think the proposal is really good and the big opportunity in making the current state of work public is that the HPC community can take a look at it, think about it, comment on it, and possibly improve it. It is already online: http://openmp.org/wp/openmp-specifications/.
Hoping for constructive feedback and taking the additional time to work on the OpenMP for Accelerator extension, the current plan is to come up with a second draft for public comment (RC2) in January 2013 and then finalize the standard quickly after. Quickly in terms of a few weeks. This plan is still ambitious, but I think this is a good plan.
If you want to learn more, come to the OpenMP booth, and come to the BoF on Tuesday afternoon, 17:30h, which unluckily I will not be able to attend myself :-/. Listen to what the people will show you and let us know what you like and what you dislike.
These are just some announcements of upcoming events in which I am involved in a varying degree. The first two will be take place at RWTH Aachen University and attendance is free of charge, the second is part of the SC12 conference in Salt Lake City, UT in the US.
Tuning for bigSMP HPC Workshop – aixcelerate (October 8th – 10th, 2012). The number of cores per processor chip is increasing. Today’s “fat” compute nodes are equipped with up to 16 eight-core Intel Xeon processors, resulting in 128 phyiscal cores, with up to 2 TB of main memory. Furthermore, special solutions like a ScaleMP vSMP system may consist of 16 nodes with 4 eight-core Intel Xeon processors each and 4 TB of accumulated main memory, scaling the number of cores even further up to 1024 per machine. While message-passing with MPI is the dominating paradigm for parallel programming in the domain of high performance computing (HPC), with the growing number of cores per cluster node the combination of MPI with shared memory programming is gaining importance. The efficient use of these systems also requires NUMA-aware data management. In order to exploit different levels of parallelism, namely through shared memory programming within a node and message-passing across the nodes, obtaining good performance becomes increasingly difficult. This tuning workshop will in detail cover tools and methods to program big SMP systems. The first day will focus on OpenMP programming on big NUMA systems, the second day will focus on Intel Performance Tools as well as the ScaleMP machine, and the third day will focus on Hybrid Parallelization. Attendees are kindly requested to prepare and bring in their own code, if applicable. If you do not have an own code, but you are interested in the presented topics, you may work on prepared exercises during the lab time (hands-on). It is recommended to have good knowledge in MPI and/or OpenMP. More details and the registration link can be found at the event website.
OpenACC Tutorial Workshop (October 11th to 12th, 2012). OpenACC is a directive-based programming model for accelerators which enables delegating the responsibility for low-level (e.g. CUDA or OpenCL) programming tasks to the compiler. To this end, using the OpenACC API, the programmer can easily offload compute-intensive loops to an attached accelerator. The open industry standard OpenACC has been introduced in November 2011 and supports accelerating regions of code in standard C, C++ and Fortran. It provides portability across operating systems, host CPUs and accelerators. Up to know, OpenACC compilers exist from Cray, PGI and CAPS. During this workshop, you will work with PGI’s OpenACC implementation on Nvidia Quadro 6000 GPUs. This OpenACC workshop is divided into two parts (with separate registrations!). In the first part, we will give an introduction to the OpenACC API while focusing on GPUs. It is open for everyone who is interested in the topic. In contrast to the first part, the second part will not contain any presentations or hands-on sessions. To the second day, we invite all programmers who have their own code and want to give it a try to accelerate it on a GPU using OpenACC and with the help of our team members and Nvidia staff. More details and the registration link can be found at the event website.
Advanced OpenMP Tutorial at SC12 (November 12th, 2012). With the increasing prevalence of multicore processors, shared-memory programming models are essential. OpenMP is a popular, portable, widely supported and easy-to-use shared-memory model. Developers usually find OpenMP easy to learn. However, they are often disappointed with the performance and scalability of the resulting code. This disappointment stems not from shortcomings of OpenMP but rather with the lack of depth with which it is employed. Our “Advanced OpenMP Programming” tutorial addresses this critical need by exploring the implications of possible OpenMP parallelization strategies, both in terms of correctness and performance. While we quickly review the basics of OpenMP programming, we assume attendees understand basic parallelization concepts and will easily grasp those basics. We discuss how OpenMP features are implemented and then focus on performance aspects, such as data and thread locality on NUMA architectures, false sharing, and private versus shared data. We discuss language features in-depth, with emphasis on features recently added to OpenMP such as tasking. We close with debugging, compare various tools, and illustrate how to avoid correctness pitfalls. More details can be found on the event website.