6963 midterm review

7/25/2019 6963 Midterm Review

1/20

CS6235

Review for Midterm


2/20

Review for Midterm

2CS6235

Administrative

Pascal will meet the class on Wednesday

- I will join at the beginning for questions on test Midterm

- In class March 28, can bring single age of notes

- !e"iew notes, readings and re"iew lecture

- Prior e#ams co"ered, will be discussed today

$esign !e"iew- Intermediate assessment of rogress on roject, oral and short

- In class %ril &

'inal rojects- Poster session, %ril 2( )dry run %ril *8+

- 'inal reort, May (


3/20

Review for Midterm

3CS6235

Parts of ExamI $efinitions

% list of terms you will be as.ed to define

II /hort %nswer )& questions, 20 oints+- 1nderstand basic P1 architecture3 rocessors and memory hierarchy

- 4igh le"el questions on more recent 5attern and alication6 lectures

III Problem /ol"ing 7 tyes of questions

- %nalye data deendences and data reuse in code and use this to guide

91$% aralleliation and memory hierarchy maing- i"en some 91$% code, indicate whether global memory accesses will be

coalesced and whether there will be ban. conflicts in shared memory

- i"en some 91$% code, add synchroniation to deri"e a correct

imlementation

-i"en some 91$% code, ro"ide an otimied "ersion that will ha"e fewerdi"ergent branches

I: );rief+


4/20

Review for Midterm

4CS6235

Syllabus

>*3 Introduction and 91$% ?"er"iew

@ot much thereA

>23 4ardware ( D >&3 Memory 4ierarchy3 >ocality and $ata Placement

Memory latency and memory bandwidth otimiations

!euse and locality What are the different memory saces on the de"ice, who can

readEwrite themC

4ow do you tell the comiler that something belongs in a articularmemory saceC

Biling transformation )to fit data into constrained storage+3 /afetyand rofitability


5/20

Review for Midterm

5CS6235

Syllabus

> D >F3 Memory 4ierarchy III3 Memory ;andwidth?timiation

Biling )for registers+ ;andwidth 7 ma#imie utility of each memory cycle

Memory accesses in scheduling )half-war+

1nderstanding global memory coalescing )for comute

caability G *2 and H *2+ 1nderstanding shared memory ban. conflicts

>3 Writing 9orrect Programs

!ace condition, deendence

What is a reduction comutation and why is it a good matchfor a P1C What does JJsyncthreads )+ doC )barrier synchroniation+

%tomic oerations

Memory 'ence Instructions

$e"ice emulation mode


6/20

Review for Midterm

6CS6235

Syllabus

>83 9ontrol 'low

$i"ergent branches

**3 /arse >inear %lgebra on P1/

$ifferent sarse matri# reresentations

/tencil comutations using sarse matrices


7/20

Review for Midterm

7CS6235

Syllabus

>*2, >*( and >*&3 %lication case studies

4ost tiling for constant cache )lus data structure reorganiation+

!elacing trig function intrinsic calls with hardware imlementations

lobal synchroniation for MPMEIMP

>*3 $ynamic /cheduling Bas. queues

/tatic queues, dynamic queues

Wait-free synchroniation

>*F3 /orting 1sing a hybrid algorithm for different sied lists

%"oiding synchroniation

Bradeoff between additional comutation and eliminating costlysynchroniation


8/20

Review for Midterm8CS6235

2010 Exam: Problem III.aa Manain memory bandwidt!

i"en the following 91$% code, how would you rewrite to imro"e bandwidth to

global memory and, if alicable, shared memoryC ?9R/ *2EF&Q

float aL*2, bL*2, cL*2L*2Q

JJglobal comute)float a, float Sb, float Sc+ T

int t# threadId##Q

int b# bloc.Id##Q

for )j b#SF&Q jG )b#SF&+NF&Q jNN+

aLt# aLt# - cLt#Lj S bLjQ

U


9/20

Review for Midterm9CS6235

Exam: Problem III.aa Manain memory bandwidt!

i"en the following 91$% code, how would you rewrite to imro"e bandwidth to

global memory and, if alicable, shared memoryC ?9R/ *2EF&Q



int t# threadId##Q

int b# bloc.Id##Q

for )j b#SF&Q jG )b#SF&+NF&Q jNN+

aLt# aLt# - cLt#Lj S bLjQ

U

How to solve?

Copy ! to s"#red memoryi$ o#lesed order

%ile i$ s"#red memory

Copy # to re&ister

Copy ' to s"#red memory(

o$st#$t memory or te)t*re

memory


10/20

Review for Midterm+,CS6235

Exam: Problem III.a@ *2Q @1M;>?9R/ *2EF&Q


float tmaQ


JJsharedJJ ctmL*02&N(2Q EE letVs use (2#(2

EE ad for ban. conflicts

int t# threadId##Q

int b# bloc.Id##Q

tma aLt#Q

Pad* t#E(2Q Pad2 jE(2Q

for )jj b#SF&Q jjG )b#SF&+NF&Q jjN(2+ for )jjjQ jGjjN2Q jNN+

9tmLjS*2Nt#Nad* cLjLt#Q

JJsyncthreads)+Q

tma tma - ctmLt#S*2 N j N ad2 S bLjQ

How to solve?

Copy ! to s"#red memoryi$ o#lesed order

%ile i$ s"#red memory

Copy # to re&ister

Copy ' to s"#red memory(

o$st#$t memory or te)t*re

memory


11/20

Review for Midterm++CS6235

2010 Exam: Problem III.bb "iverent #ran$!i"en the following 91$% code, describe how you would modify this to deri"e an

otimied "ersion that will ha"e fewer di"ergent branches AMain)+ T float hJaL*02&, hJbL*02&Q

A ES assume aroriate cudaMalloc called to create dJa and dJb, and dJa is SE

ES initialied from hJa using aroriate call to cudaMemcy SE

dim( dimbloc.)2F+Q dim( dimgrid)&+Q comuteGGGdimgrid, dimbloc.,0HHH)dJa,dJb+Q ES assume dJb is coied bac. from the de"ice using call to cudaMemcy SEU

JJglobalJJ comute )float Sa, float Sb+ Tfloat aL&L2F, bL&L2FQint t# threadId##Q b# bloc.Id##Qif )t# *F 0+

)"oid+ startingJ.ernel )aLb#Lt#, bLb#Lt#+Qelse ES )t# *F H 0+ SE )"oid+ defaultJ.ernel )aLb#Lt#, bLb#Lt#+Q

U

-ey ide#.Sep#r#te m*ltiples of +6

from ot"ers


12/20

Review for Midterm+2CS6235

Problem III.b

%roach3

!enumber thread to concentrate case where notdi"isible by *F

if )t# G 2&0+ t t# N )t#E*F+ N *Q


13/20


2010 Exam: Problem III.$c %ilinBhe following sequential image correlation comutation comares a region of an image to

a temlate /how how you would tile the image and threshold data to fit in *28M;global memory and the temlate data to fit in a *FR; shared memoryC


14/20


&iew of 'om(utation

Perform correlation of temlate with ortion of image

Mo"e 5window6 horiontally and downward and reeat

im#&e

templ#te


15/20


2010 Exam: Problem III.$

i 4ow big is image and temlate dataC

Image *K22

S & bytesEint *00 MbytesBh *00 Mbytes

Bemlate F&2S & bytes Eint e#actly *FR;ytes

Botal data set sie H 200 Mbytes

9annot ha"e both image and Bh in global memory 7 must generate2 tiles

Bemlate data does not fit in shared memory due to other thingslaced thereA

ii Partitioning to suort tiling for shared memory

4int to e#loit reuse on temlate by coying to shared memory

9ould also e#loit reuse on ortion of image

$eendences only on th )a reduction+


16/20


2010 Exam: Problem III.$

)iii+ @eed to show tiling for temlate

9an coy into shared memory in coalesced order

9oy half or less at a time


17/20


2010 Exam: Problem III.dd Parallel (artitionin and syn$!roni)ation *+, "e$om(osition-

Without writing out the 91$% code, consider a 91$% maing of the >1 $ecomosition

sequential code below %nswer should be in three arts, ro"iding oortunities forartial credit3 )i+ where are the data deendences in this comutationC )ii+ how would youartition the comutation across threads and bloc.sC )iii+ how would you addsynchroniation to a"oid race conditionsC

float aL*02&L*02&Q

for ).0Q jG*02(Q .NN+ T

for )i.N*Q iG*02&Q iNN+

aLiL. aLiL. E aL.L.Q


for )j.N*Q jG*02&Q jNN+

aLiLj aLiLj 7 aLiL.SaL.LjQ

U


18/20


2010 Exam: Problem III.dd Parallel (artitionin and syn$!roni)ation *+, "e$om(osition-

Without writing out the 91$% code, consider a 91$% maing of the >1 $ecomosition

sequential code below %nswer should be in three arts, ro"iding oortunities forartial credit3 )i+ where are the data deendences in this comutationC )ii+ how would youartition the comutation across threads and bloc.sC )iii+ how would you addsynchroniation to a"oid race conditionsC

float aL*02&L*02&Q

for ).0Q jG*02(Q .NN+ T


aLiL. aLiL. E aL.L.Q


for )j.N*Q jG*02&Q jNN+

aLiLj aLiLj 7 aLiL.SaL.LjQ

U

-ey /e#t*res of Sol*tio$.

i01epe$de$es.

%r*e #i(#(#i(#i #rried 'y

%r*e #i(#( #i(#i( #rried 'y %r*e #i(#i( #i( #( #rried 'y

ii0#rtitio$.

Mer&e i loops( i$ter"#$&e wit" ( p#rtitio$

ross 'los:t"re#ds ;s*ffiie$t


19/20


2011 Exam: Exam(les of s!ort answers

a $escribe how you can e#loit satial reuse inotimiing for memory bandwidth on a P1 )Partialcredit3 what are the memory bandwidth otimiationswe studiedC+

b i"en e#amles we ha"e seen of control flow inP1 .ernels, describe ?@< way to reduce di"ergentbranches for ?@< of the following3 consider tree-structured reductions, e"en-odd comutations, orboundary conditions

c !egarding floating oint suort in P1s, how doesthe architecture ermit trading off recision and

erformanceC d What haens if two threads assigned to

different bloc.s write to the same memory locationin global memoryC


20/20

Review for Midterm2,CS6235

2011 Exam: Exam(les of Essay

Pic. one of the following three toics and write a "erybrief essay about it, no more than ( sentences

a We tal.ed about sarse matri# comutations withresect to linear algebra, grah coloring and rogramanalysis $escribe a sarse matri# reresentationthat is aroriate for a P1 imlementation of oneof these alications and e#lain why it is well suited

b We tal.ed about how to ma tree-structuredcomutations to P1s ;riefly describe features ofthis maing that would yield an efficient P1imlementation

c We tal.ed about dynamic scheduling on a P1$escribe a secific strategy for dynamic scheduling)static tas. list, dynamic tas. list, wait-freesynchroniation+ and when it would be aroriate touse it

6963 midterm review

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