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János Végh

Publications and source records attributed to János Végh.

25 records · Page 2Linked to original sources
arXiv2018

Renewing computing paradigms for more efficient parallelization of single-threads

Computing is still based on the 70-years old paradigms introduced by von Neumann. The need for more performant, comfortable and safe computing forced to develop and utilize several tricks both in hardware and software. Till now technology enabled to increase performance without changing the basic computing paradigms. The recent stalling of single-threaded computing performance, however, requires to redesign computing to be able to provide the expected performance. To do so, the computing paradigms themselves must be scrutinized. The limitations caused by the too restrictive interpretation of the computing paradigms are demonstrated, an extended computing paradigm introduced, ideas about changing elements of the computing stack suggested, some implementation details of both hardware and software discussed. The resulting new computing stack offers considerably higher computing throughput, simplified hardware architecture, drastically improved real-time behavior and in general, simplified and more efficient computing stack.

cs.DC↗
arXiv2017

How Amdahl's low restricts supercomputer applications and building ever bigger supercomputers

This paper reinterprets Amdahl's law in terms of execution time and applies this simple model to supercomputing. The systematic discussion results in practical formulas enabling to calculate expected running time using large number of processors from experimental runs using low number of processors, delivers a quantitative measure of computational efficiency of supercomputing applications. Through separating non-parallelizable contribution to fractions according to their origin, Amdahl's law enables to derive a timeline for supercomputers (quite similar to Moore's law) and describes why Amdahl's law limits the size of supercomputers. The paper validates that Amdahl's 50-years old model (with slight extension) correctly describes the performance limitations of the present supercomputers. Using some simple and reasonable assumptions, the absolute performance bound of supercomputers is concluded, furthermore that serious enhancements are still necessary to achieve the exaFLOPS dream value.

cs.DC↗
arXiv2016

A new kind of parallelism and its programming in the Explicitly Many-Processor Approach

The processor accelerators are effective because they are working not (completely) on principles of stored program computers. They use some kind of parallelism, and it is rather hard to program them effectively: a parallel architecture by means of (and thinking in) sequential programming. The recently introduced EMPA architecture uses a new kind of parallelism, which offers the potential of reaching higher degree of parallelism, and also provides extra possibilities and challenges. It not only provides synchronization and inherent parallelization, but also takes over some duties typically offered by the OS, and even opens the till now closed machine instructions for the end-user. A toolchain for EMPA architecture with Y86 cores has been prepared, including an assembler and a cycle-accurate simulator. The assembler is equipped with some meta-instructions, which allow to use all advanced possibilities of the EMPA architecture, and at the same time provide a (nearly) conventional-style programming. The cycle accurate simulator is able to execute the EMPA-aware object code, and is a good tool for developing algorithms for EMPA

cs.DC↗
arXiv2016

Comments on the parallelization efficiency of the Sunway TaihuLight supercomputer

In the world of supercomputers, the large number of processors requires to minimize the inefficiencies of parallelization, which appear as a sequential part of the program from the point of view of Amdahl's law. The recently suggested new figure of merit is applied to the recently presented supercomputer, and the timeline of "Top 500" supercomputers is scrutinized using the metric. It is demonstrated, that in addition to the computing performance and power consumption, the new supercomputer is also excellent in the efficiency of parallelization. Based on the suggested merit, a "Moore-law" like observation is derived for the timeline of parallelization efficacy of supercomputers.

cs.DC↗
arXiv2016

A figure of merit for describing the performance of scaling of parallelization

With the spread of multi- and many-core processors more and more typical task is to re-implement some source code written originally for a single processor to run on more than one cores. Since it is a serious investment, it is important to decide how much efforts pays off, and whether the resulting implementation has as good performability as it could be. The Amdahl's law provides some theoretical upper limits for the performance gain reachable through parallelizing the code, but it needs the detailed architectural knowledge of the program code, does not consider the housekeeping activity needed for parallelization and cannot tell how the actual stage of parallelization implementation performs. The present paper suggests a quantitative measure for that goal. This figure of merit is derived experimentally, from measured running time, and number of threads/cores. It can be used to quantify the used parallelization technology, the connection between the computing units, the acceleration technology under the given conditions, communication method within SoC, or the performance of the software team/compiler.

cs.PF↗
arXiv2016

A configurable accelerator for manycores: the Explicitly Many-Processor Approach

A new approach to designing processor accelerators is presented. A new computing model and a special kind of accelerator with dynamic (end-user programmable) architecture is suggested. The new model considers a processor, in which a newly introduced supervisor layer coordinates the job of the cores. The cores have the ability (based on the parallelization information provided by the compiler, and using the help of the supervisor) to outsource part of the job they received to some neighbouring core. The introduced changes essentially and advantageously modify the architecture and operation of the computing systems. The computing throughput drastically increases, the efficiency of the technological implementation (computing performance per logic gates) increases, the non-payload activity for using operating system services decreases, the real-time behavior changes advantageously, and connecting accelerators to the processor greatly simplifies. Here only some details of the architecture and operation of the processor are discussed, the rest is described elsewhere.

cs.DC↗