Publications

Performance to Power and Performance to Cost Ratios with Intel Xeon Phi Coprocessors (and why 1x Acceleration May Be Enough)

January 27, 2015

The paper studies two performance metrics of systems enabled with Intel Xeon Phi coprocessors: the ratio of performance to consumed electrical power and the ratio of performance to purchasing system cost, both under the assumption of linear parallel scalability of the application. Performance to power values are measured for three workloads: a compute-bound workload (DGEMM), a memory bandwidth-bound workload (STREAM), and a latency-limited workload (small matrix LU decomposition). Performance to cost ratios are computed, using system configurations and prices available at Colfax International, as functions of the acceleration factor and of the number of coprocessors per system. That study considers hypothetical applications with acceleration factor from 0.35x to 2x. In all studies, systems with Intel Xeon Phi coprocessors yield better metrics than systems with only Intel Xeon processors. That applies even with acceleration factor of 1x, as long as the application can be distributed between the CPU and the coprocessor. Complete paper:  Colfax_1x.pdf (321 KB) — this file is [...]

Fine-Tuning Vectorization and Memory Traffic on Intel Xeon Phi Coprocessors: LU Decomposition of Small Matrices

January 27, 2015

Common techniques for fine-tuning the performance of automatically vectorized loops in applications for Intel Xeon Phi coprocessors are discussed. These techniques include strength reduction, regularizing the vectorization pattern, data alignment and aligned data hint, and pointer disambiguation. In addition, the loop tiling technique of memory traffic tuning is shown. The optimization methods are illustrated on an example of single-threaded LU decomposition of a single precision matrix of size 128×128. Benchmarks show that the discussed optimizations improve the performance on the coprocessor by a factor of 2.8 compared to the unoptimized code, and by a factor of 1.7 on the multi-core host system, achieving roughly the same performance on the host and on the coprocessor. The code discussed in the paper can be freely downloaded from this page. Complete paper:  Colfax_LU.pdf (604 KB) — this file is available only to registered users. Register or Log In. Source code for Linux: colfax-lu.tgz (17 KB) — this archive is available only to registered users. Register or [...]

Intel Cilk Plus for Complex Parallel Algorithms: “Enormous Fast Fourier Transforms” (EFFT) Library

September 18, 2014

In this paper we demonstrate the methodology for parallelizing the computation of large one-dimensional discrete fast Fourier transforms (DFFTs) on multi-core Intel Xeon processors. DFFTs based on the recursive Cooley-Tukey method have to control cache utilization, memory bandwidth and vector hardware usage, and at the same time scale across multiple threads or compute nodes. Our method builds on single-threaded Intel Math Kernel Library (MKL) implementation of DFFT, and uses the Intel Cilk Plus framework for thread parallelism. We demonstrate the ability of Intel Cilk Plus to handle parallel recursion with nested loop-centric parallelism without tuning the code to the number of cores or cache metrics. The result of our work is a library called EFFT that performs 1D DFTs of size 2^N for N>=21 faster than the corresponding Intel MKL parallel DFT implementation by up to 1.5x, and faster than FFTW by up to 2.5x. The code of EFFT is available for free download under the GPLv3 license. This work provides a new efficient DFFT implementation, and at the same time demonstrates an [...]

Installing Intel MPSS 3.3 in Arch Linux

August 20, 2014

This technical publication provides instructions for installing the Intel Manycore Platform Software Stack (MPSS) version 3.3 in Arch Linux operating system. Intel MPSS is a suite of tools necessary for operation of Intel Xeon Phi coprocessors. Instructions provided here enable offload and networking functionality for coprocessors in Arch Linux. The procedure described in this paper is completely reversible via an uninstallation script. Downloads: Product Direct Link Intel MPSS 3.3 (page, archive) mpss-3.3-linux.tar (~400 MB) Linux Kernel 3.10 LTS (AUR) linux-lts310.tar.gz (78 KB) TRee Installation Generator (TRIG) trig.sh (3 KB) — this archive is available only to registered users. Register or Log In. RHEL networking utilities rhnet.tgz (34 KB) — this archive is available only to registered users. Register or Log In. Offload functionality test Offload-Hello.cc (347 B) — this archive is available only to registered users. Register or Log In. GNU Public License v2 (applies to TRIG and RHEL utilities) page Paper:  Colfax_MPSS_in_Arch_Linux.pdf (97 KB) — [...]

File I/O on Intel Xeon Phi Coprocessors: RAM disks, VirtIO, NFS and Lustre

July 28, 2014

The key innovation brought about by Intel Xeon Phi coprocessors is the possibility to port most HPC applications to manycore computing accelerators without code modification. One of the reasons why this is possible is support for file input/output (I/O) directly from applications running on coprocessors. These facilities allow seamless usage of manycore accelerators in common HPC tasks such as application initialization from file data, saving running output, checkpointing and restarting, data post-processing and visualization, and other. This paper provides information and benchmarks necessary to make the choice of the best file system for a given application from a number of the available options: RAM disks, virtualized local hard drives, and distributed storage shared with NFS or Lustre. We report benchmarks of I/O performance and parallel scalability on Intel Xeon Phi coprocessors, strengths and limitations of each option. In addition, the paper presents system administration procedures necessary for using each file system on coprocessors, including bridged networking and [...]

Colfax Research papers translated to Japanese

July 14, 2014

With the help of our partners at Intel, some of our articles on Intel Xeon Phi coprocessor programming were translated to the Japanese language. インテル社の協力で、弊社のインテル(R) Xeon Phi(TM) コプロセッサーのプログラミングについての白書の一部が日本語に翻訳されました。 Original: Configuration and Benchmarks of Peer-to-Peer Communication over Gigabit Ethernet and InfiniBand in a Cluster with Intel Xeon Phi Coprocessors Translation:  JP-Colfax_InfiniBand_for_MIC.pdf (2 MB) — this file is available only to registered users. Register or Log In. Original: Heterogeneous Clustering with Homogeneous Code: Accelerate MPI Applications Without Code Surgery Using Intel Xeon Phi Coprocessors Translation:  JP-Colfax_Heterogeneous_Clustering_Xeon_Phi.pdf (657 KB) — this file is available only to registered users. Register or Log In. Original: Multithreaded Transposition of Square Matrices with Common Code for Intel Xeon Processors and Intel Xeon Phi Coprocessors Translation:  JP-Colfax_Transposition-7110P.pdf (987 [...]

Cluster-Level Tuning of a Shallow Water Equation Solver on the Intel MIC Architecture

May 12, 2014

The paper demonstrates the optimization of the execution environment of a hybrid OpenMP+MPI computational fluid dynamics code (shallow water equation solver) on a cluster enabled with Intel Xeon Phi coprocessors. The discussion includes: Controlling the number and affinity of OpenMP threads to optimize access to memory bandwidth; Tuning the inter-operation of OpenMP and MPI to partition the problem for better data locality; Ordering the MPI ranks in a way that directs some of the traffic into faster communication channels; Using efficient peer-to-peer communication between Xeon Phi coprocessors based on the InfiniBand fabric. With tuning, the application has 90% percent efficiency of parallel scaling up to 8 Intel Xeon Phi coprocessors in 2 compute nodes. For larger problems, scalability is even better, because of the greater computation to communication ratio. However, problems of that size do not fit in the memory of one coprocessor. The performance of the solver on one Intel Xeon Phi coprocessor 7120P exceeds the performance on a dual-socket Intel Xeon E5-2697 v2 CPU by a [...]

Configuration and Benchmarks of Peer-to-Peer Communication over Gigabit Ethernet and InfiniBand in a Cluster with Intel Xeon Phi Coprocessors

March 11, 2014

Intel Xeon Phi coprocessors allow symmetric heterogeneous clustering models, in which MPI processes are run fully on coprocessors, as opposed to offload-based clustering. These symmetric models are attractive, because they allow effortless porting of CPU-based applications to clusters with manycore computing accelerators. However, with the default software configuration and without specialized networking hardware, peer-to-peer communication between coprocessors in a cluster is quenched by orders of magnitude compared to the capabilities of Gigabit Ethernet networking hardware. This situation is remedied by InfiniBand interconnects and the software supporting them. In this paper we demonstrate the procedures for configuring a cluster with Intel Xeon Phi coprocessors connected with Gigabit Ethernet as well as InfiniBand interconnects. We measure and discuss the latencies and bandwidths of MPI messages with and without the advanced configuration with InfiniBand support. The paper contains a discussion of MPI application tuning in an InfiniBand-enabled cluster with Intel Xeon Phi [...]

“Heterochromic” Computer and Finding the Optimal System Configuration for Medical Device Engineering

January 27, 2014

Designing a computing system configuration for optimal performance of a given task is always challenging, especially if the acquisition budget is fixed. It is difficult, if not impossible, to analytically resolve all of the following questions: How well does the application scale across multiple cores? What is the efficiency and scalability of the application with accelerators (GPGPUs or coprocessors)? Should measures be taken to prevent I/O bottlenecks? Is it more efficient to scale up a single task or partition the system for multiple tasks? What combination of CPU models, accelerator count, and per-core software licenses gives the best return on investment? Rigorous benchmarking is the most reliable method of ensuring the “best bang for buck”, however, it requires access to the computing systems of interest. Colfax takes pride in being able to offer interested customers opportunities for deducing the optimal configuration for specific tasks. Recently we received a request from Peter Newman, Systems Engineer at Carestream Health, for evaluating the performance of the [...]

Parallel Computing in the Search for New Physics at LHC

December 2, 2013

In the past few months we have had the pleasure of collaborating with Prof. Valerie Halyo of Princeton University on modernization of a high energy physics application for the needs of the Large Hadron Collider (LHC). The objective of our project is to improve the performance of the trigger at LHC, so as to enable real-time detection of exotic collision event products, such as black holes or jets. For the numerical algorithm of the new trigger software, the Hough transform was chosen. This method allows fast detection of straight or curved tracks in a set of points (detector hits), which could be the traces of new exotic particles. The nature of the numerical Hough transform is highly parallelizable, however, existing implementations did not use hardware parallelism or used it sub-optimally. Colfax’s role in the project was to optimize a thread-parallel implementation of the Hough transform for multi-core processors. The result of our involvement was a code capable of detecting 5000 tracks in a synthetic dataset 250x faster than prior art, on a multi-core desktop CPU. By [...]
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