This work presents a hybrid computing approach which combines GPUs and multicore processors to fully take advantage of the computing power latent in modern computers. It also presents its application to the problem of tomographic reconstruction. One inherent characteristic of these modern platforms is their heterogeneity, which raises the issue of workload distribution among the different processing elements. Adaptive load balancing techniques are thus necessary to properly adjust the amount of work to be done by each computing element. Here, we have chosen the 'on-demand' strategy, a well-known technique in the HPC field by which the different elements asynchronously request a piece of work when they become idle, thereby keeping the system fairly well balanced. The results show that our scheme accommodates to the heterogeneous platform where it runs as it assigns more work to the faster processing elements automatically, which allows to correctly exploit all the resources available and to get complete reconstructions in less time than pure CPU or GPU approaches.

Electron tomography (ET) allows elucidation of the three-dimensional (3D) structure of large complex biological specimens at molecular resolution. In order to achieve such resolution levels, large projection images have to be used to compute the 3D reconstructions. Tomographic reconstruction on this scale requires a tremendous use of computational resources and considerable processing time. Traditionally, parallel and distributed systems, and more recently GPUs, have been the key to cope with this demanding procedure. This work demonstrates that full exploitation of the impressive processing power within modern multi-core processors make them a feasible alternative. The use of parallel computing, vectorization and code optimization allows ultra-fast tomographic reconstructions on standard computers, even outperforming GPUs. Our results confirm that modern processors succeed in providing reconstructed volumes in very little time, which enables them for real-time ET.

Abstract Summary: Tomo3D implements a multithreaded vectorized approach to tomographic reconstruction that takes full advantage of the computer power in modern multicore computers. Full resolution tomograms are generated at high speed on standard computers with no special system requirements. Tomo3D has the most common reconstruction methods implemented, namely weighted Back-projection (WBP) and simultaneous iterative reconstruction technique (SIRT). It proves to be competitive with current graphic processor unit solutions in terms of processing time, in the order of a few seconds with WBP or minutes with SIRT. The program is compatible with standard packages, which easily allows integration in the electron tomography workflow. Availability: http://www.cnb.csic.es/%7ejjfernandez/tomo3d Contact: [email protected] Supplementary information: Supplementary data are available at Bioinformatics online.

Electron tomography (ET) allows elucidation of the three-dimensional (3D) structure of large complex biological specimens at molecular resolution. In order to achieve such resolution levels, large projection images have to be used to compute the 3D reconstructions. Tomographic reconstruction on this scale requires a tremendous use of computational resources and a considerable processing time. In this work, we present and evaluate a highly optimized implementation of the Weighted Back-Projection reconstruction algorithm. Briefly, optimizations made to the code comprise (1) vector processing with SSE (Streaming SIMD Extensions) instructions, (2) an efficient use of cache memory, (3) to take advantage of the inherent image symmetry, (4) to use the FFTW (Fastest Fourier Transform in the West) library for image filtering, (5) to use regions of interest and last, but not least, (6) a wide range of minor optimizations like some data pre-calculations or an instruction level parallelism improvement. We have evaluated the method on tomographic reconstructions of several datasets and on two computing platforms. The results show that our version speeds up the method by a factor around 14 or 16, depending on the platform.

Electron tomography allows elucidation of the three-dimensional (3D) structure of large complex biological specimens at molecular resolution. In order to achieve such resolution levels, large projection images have to be used to compute the 3D reconstructions. Tomographic reconstruction on this scale requires a tremendous use of computational resources and considerable processing time. In this work, we present and evaluate a vector approach for fast 3D reconstruction that takes advantage of the multimedia extensions in modern processors. We have implemented the standard 3D reconstruction method, weighted backprojection, using the Streaming SIMD Extensions (SSE). We have evaluated the method on tomographic reconstruction of several datasets of various sizes on a computing platform based on Intel Xeon processor. The results show that our approach speeds up the method by a factor of 3.