Introduction to Data-Oriented Design.ppt

1、Introduction to Data-Oriented Design,So what is this Data-Oriented Design?,Its about on shifting focus to how data is read and written,Why should we care?,Performance,A read from memory takes 600 cycles at 3.2 GHz,A read from memory takes 40 cycles at 300 MHz,Performance,Disks (Blu-ray/DVD/HDD),Main

2、 Memory,L2 Cache,L1 Cache,CPU / Registers,Latency,:(,600 cycles,40 cycles,1 2 cycles,Multithreading,Object,Read?,Write?,Object,update(),Object,Cannot multithread without knowing how data is touched Adding locks always protects data not code,Read?,Write?,Read?,Write?,Offloading to co-unit,?,SPU/GPU/A

3、PU,?,If data is unknown hard/impossible to run on co-unit,Better design,Data focus can lead to isolated, self-contained, interchangeable pieces of data and code This can make it easier to test data and code in isolation,Example - OOD,class Bot .Vec3 m_position;.float m_mod;.float m_aimDirection;.voi

4、d updateAim(Vec3 target)m_aimDirection = dot3(m_position, target) * m_mod; ,icache-miss,data-miss,Unused cached data,Very hard to optimize!,Example - OOD,void updateAim(Vec3 target) m_aimDirection = dot3(m_position, target) * m_mod; ,Lets say we call this code 4 times (4 diffrent Bots),iCache 600,m_

5、position 600,m_mod - 600,aimDir 100,20 cycles,iCache 600,m_position 600,m_mod - 600,aimDir 100,iCache 600,m_position 600,m_mod - 600,aimDir 100,iCache 600,m_position 600,m_mod - 600,aimDir 100,7680,Example - DOD,Design ”back to front” and focus on the output data Then add the minimal amount of data

6、needed to do the transform to create the correct output,Example - DOD,void updateAims(float* aimDir,const AimingData* aim,Vec3 target, uint count) for (uint i = 0; i positionsi,target) * aim-modi; ,Only read needed inputs,Write to linear array,Loop over all the data,Actual code unchanged,What has ch

7、anged?,Code separated,Example - DOD,void updateAims(float* aimDir, const AimingData* aim, Vec3 target, uint count) for (uint i = 0; i positionsi, target) * aim-modi; ,iCache 600,positions 600,mod - 600,aimDir 100,20 cycles,1980,Data layout OOD vs DOD,pos0,mod0,aimDir0,pos0,Pos1,mod1,aimDir1,pos0,pos

8、0,pos0,pos1,pos1,pos1,pos1,pos2,pos2,pos2,pos2,pos3,pos3,pos3,pos3,mod0,mod1,mod2,mod3,aimDir0,aimDir1,aimDir2,aimDir3,pos0,pos0,pos0,Each color block is one 128 byte cache line,Its all about memory,Optimize for data first then code Most code is likely bound by memory access Not everything needs to

9、be an object,Remember,We are doing games, we know our data. Pre-format. Source data and native data doesnt need to be the same,Example: Area Triggers,position,position,position,position,next,position,position,position,position,next,position,position,position,position,next,Source data (Linked List),N

10、ative Data (Array),position,position,position,position,position,position,position,position,position,position,position,position,position,position,count,Example: Culling System,Old System,New System (Linear arrays and brute force),3x faster, 1/5 code size, simpler,Data Oriented Design Delivers:,Better

11、 Performance,Often simpler code,More parallelizable code,Questions?,Links,Data-Oriented Design (Or Why You Might Be Shooting Yourself in The Foot With OOP) http:/ Practical Examples in Data Oriented Design http:/ The Latency Elephant http:/seven-degrees-of- Pitfalls of Object Oriented Programming ht

12、tp:/seven-degrees-of- Insomniac R&D http:/ CellPerformance,Image credits,Cat image: http:/ photo by: Arinn capped and submitted by: Andy Playstation 3 and Playstation 2 Copyright to Sony Computer Entertainment Xbox 360 Image Copyright to Microsoft “WTF” Code quality image: Copyright by Thom Holwerda http:/