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Abstract Evaluating the Impact of Memory System Performance on Software Prefetching and Loc

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EvaluatingtheImpactofMemorySystemPerformanceon

SoftwarePrefetchingandLocalityOptimizations

AneeshAggarwal

Abdel-HameedA.BadawyChau-WenTseng

DonaldYeung

ElectricalandComputerEngineeringDept.Dept.ofComputerScience

UniversityofMaryland,CollegeParkUniversityofMaryland,CollegePark

Abstract

Softwareprefetchingandlocalityoptimizationsaretech-niquesforovercomingthegapbetweenprocessorand

memoryspeeds.UsingtheSimpleScalarsimulator,we

evaluatetheimpactofmemorybandwidthandlatency

ontheeffectivenessofsoftwareprefetchingandlocality

optimizationsonthreetypesofapplications:regularsci-entificcodes,irregularscientificcodes,andpointer-based

codes.Wefindsoftwareprefetchinghidesmemorycosts

butincreasesinstructioncountandrequiresgreatermem-

orybandwidth.Localityoptimizationschangethecom-

putationorderanddatalayoutatcompileorruntimetoeliminatecachemisses,reducingmemorycostswithout

requiringmorememorybandwidth.Combiningprefetch-

ingandlocalityoptimizationscanimproveperformance,

butinteractionscanalsonullifythebenefitsofprefetching.Weproposeseveralalgorithmstobetterintegratesoftware

prefetchingandlocalityoptimizations.

1Introduction

Evenwithlargeon-chipcaches,currentmicroprocessors

spendalargepercentageofexecutiontimeonmemoryac-

cessstalls.Sinceprocessorspeedsaregrowingatagreater

ratethaneithermemoryandnetworkspeeds,weexpectmemoryaccesscoststobecomeevenmoreimportant.In

thenottoodistantfuture,itwillnotbefarfromthetruth

tosayinstructionsarefreeandperformanceisdetermined

TechnicalReportCS-TR-4169(alsoUMIACS-TR-2000-57),Dept.ofComputerScience,UniversityofMaryland,July2000onlybymemoryaccesscosts.Computerarchitectshavebeenbattlingthismemorywallbydesigningeverlarger

andsophisticatedcaches.However,asapplicationsstart

usingpointer-basedlinkeddatastructuresandperforming

irregularmemoryaccesses,cachesnolongerperformwell

withoutadditionalhelp.Twoapproachestoimprovingcacheperformanceare

softwareprefetchingandlocalityoptimizations.Software

prefetchingexecutesexplicitprefetchinstructionstobe-

ginloadingdatafrommemorytocache.Iftheprefetch

beginsearlyenough,andthedataisnotevictedpriortouse,memoryaccesslatencycanbecompletelyhidden.

Memorybandwidthuseisincreased,however,sincethe

processorwillnowconsumedataatafasterrate.Incom-

parison,localityoptimizationsusecompilerorrun-time

transformationstothecomputationorderand/ordatalay-outofaprogramtoincreasetheprobabilityitaccessesdata

alreadyincache.Ifsuccessful,averagememorylatency

andbandwidtharebothreduced,sincetherewillbefewer

memoryaccesses.

Bothapproachesforavoidingthememorywallhavebeenstudiedinisolation.Inthispaper,weexaminehow

welleachapproachworksforthreetypesofdata-intensive

applications.Wealsoevaluatebothapproachesinauni-

fiedenvironment,sowecancomparetheirperformance

andinvestigatetheirinteractionswhenappliedinconcert.Finally,wealsostudytheimpactofmemorybandwidth

andlatencyontheperformanceofeachtechnique.The

contributionsofthispaperareasfollows:

Wecomparetheefficacyofsoftwareprefetching

andlocalityoptimizationsforthreetypesofdata-

intensivecodes.

1Weevaluatetheimpactofmemorybandwidthand

memorylatencyonapplicationperformancewithand

withoutprefetchingandlocalityoptimizations.

Weproposeseveralenhancementstointegratedsoft-

wareprefetchingandlocalityoptimizations.

Webegintherestofthispaperwithalookatthree

memoryaccesspatterns,thenexaminesoftwareprefetch-

ingandlocalityoptimizationsforeachtypeofapplication.Wepresentexperimentalevaluationsforeachapplication

anddevelopimprovedalgorithms.Finally,wediscuss

relatedworkandconclude.

2MemoryAccessPatterns

Thetypesofsoftwareprefetchingandlocalityoptimiza-

tionswhichmaybeappliedareseriouslydependenton

thetypeofmemoryaccesspatternmadebyaprogram.

Webeginbypresentingthreeimportanttypesofmemory

accesspatterns.

2.1AffineArrayAccesses

Themostbasicmemoryaccesspatternisaffine(linear)

accessestomultidimensionalarrays.Forinstance,con-

sidertheJacobicodeinFigure1,typicallyusedinmulti-gridsolversforpartialdifferentialequations(PDEs).The

valueofapointiniscalculatedastheaverageofvalues

ofneighboringpointsinallthreedimensionsof.This

stencilpatternisrepeatedlyappliedtoeachpointof,re-

sultinginasmoothersolution.Allarrayaccessesareaffinebecausearraysubscriptsarecombinationsofloopindex

variableswithconstantcoefficientsandadditiveconstants.

Inpractice,thearenocoefficientsandsmalladditivecon-

stantsareused.Theseprogramsarealsocalledregular

codesbecausememoryaccesspatternsaresoregularandwelldefined.

Affinearrayaccessesarecommonindense-matrixlin-

earalgebraandfinite-differencePDEsolvers,aswellas

databasescansandimageprocessing.Amajorfeatureof

affinearrayaccessesisthattheyallowmemoryaccesspat-ternstobeentirelycomputedatcompiletime,assumear-

raydimensionsizesareknown.Thisallowsbothsoftware

prefetchingandcompilertransformationstobecalculated

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计算机考研--复试英语

计算机考研--复试英语

计算机考研--复试英语

Abstract 1

In recent years, machine learning has developed rapidly, especially in the deep learning, where remarkable achievements

are obtained in image, voice, natural language processing and other fields. The expressive ability of machine learning

algorithm has been greatly improved; however, with the increase of model complexity, the interpretability of computer

learning algorithm has deteriorated. So far, the interpretability of machine learning remains as a challenge. The trained

models via algorithms are regarded as black boxes, which seriously hamper the use of machine learning in certain fields,

such as medicine, finance and so on. Presently, only a few works emphasis on the interpretability of machine learning.

Therefore, this paper aims to classify, analyze and compare the existing interpretable methods; on the one hand, it

操作系统概念第六版重点部分中文答案

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1

1.1 What are the three main purposes of an operat ing system?

1 To provide an en vir onment for a computer user to execute programs on computer

hardware in a convenient and ef ?cie nt manner.

2 To allocate the separate resources of the computer as n eeded to solve the problem

give n. The allocati on process should be as fair and ef ?cie nt as possible.

3 As a control program it serves two major functions: (1) supervision of the execution of user programs to preve

nt errors and improper use of the computer, and (2) man age- ment of the operati on and con trol of I/O devices.

环境提供者，为计算机用户提供一个环境，使得能够在计算机硬件上方便、高效的执行程序

资源分配者，为解决问题按需分配计算机的资源，资源分配需尽可能公平、高效

控制程序

监控用户程序的执行，防止岀错和对计算机的不正当使用

管理I/O设备的运行和控制

1.2 List the four steps that are n ecessary to run a program on a completely dedicatedmachi ne.

An swer: Gen erally, operati ng systems for batch systems have simpler requireme nts tha n for pers onal

MEMORY存储芯片MT29F2G08ABAEAWP IT中文规格书

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Dynamic ODT

In certain application cases, and to further enhance signal integrity on the data bus, it is

desirable that the termination strength of the DDR3 SDRAM can be changed without

issuing an MRS command, essentially changing the ODT termination on the fly. With

dynamic ODT RTT(WR)) enabled, the DRAM switches from nominal ODT RTT,nom) to dy-

namic ODT RTT(WR)) when beginning a WRITE burst and subsequently switches back to

nominal ODT RTT,nom) at the completion of the WRITE burst. This requirement is sup-

ported by the dynamic ODT feature, as described below.

Dynamic ODT Special Use Case

When DDR3 devices are architect as a single rank memory array, dynamic ODT offers a

special use case: the ODT ball can be wired high (via a current limiting resistor prefer-

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职称英语考试试题

职称英语考试试题

职称英语考试试题

一、听力理解（共20分）

Section A：短对话理解

1. What is the man going to do this weekend?

a) Visit his parents.

b) Go to a concert.

c) Work on a project.

2. Why does the woman refuse the man's invitation?

a) She has to study for an exam.

b) She is not interested in the event.

c) She has another appointment.

Section B：长对话理解

Listen to the conversation between a manager and an employee

about a new project. Choose the best answer for each question.

3. What is the main topic of the conversation?

a) The company's financial status.

b) The details of a new project.

c) The employee's performance review.

4. What is the deadline for the project?

a) One month from now.

b) Two weeks from now. c) Three days from now.

二、阅读理解（共30分）

Passage 1

In recent years, the concept of a "work-life balance" has