creating a decision framework for opencl...

CREATING A DECISION FRAMEWORK

FOR OpenCL USAGE

Graham Brown

CTO Corel Corporation

2 | Creating a Decision Framework for OpenCL Usage | June 15, 2011

AGENDA

OpenCL Overview

Corel’s View of Optimization

Sample of Corel’s Decision Framework

Additional Considerations


OpenCL OVERVIEW


QUICK POLL:

WHO IS WORKING WITH OR

INVESTIGATING OpenCL?

OR HAS A COLLEAGUE WHO

IS DOING SO?


OpenCL | KEY POINTS

Acronym for Open Computing Language

– allows cross-platform parallel programming

– Open and royalty–free standard

– Improves application speed and responsiveness

– Can leverage all computing resources (CPU, GPU, APU)

Source: Khronos.org


OpenCL | GOALS

Near transparent use of computing resources

Use GPU resources for non-graphics processing w/o impacting power

usage or graphics rendering speed

Data or task-based parallel processing

Familiar / compatible with existing programming models

Source: Khronos.org


OPENCL | History – from A to K

Created by Apple

Standardized in 2008, v1.1 released 2010

Wide industry participation

Maintained and evolved by Khronos

Source: Khronos.org

http://www.khronos.org


GPU PROCESSING | IHV Support

– GPU first supported as ATI Stream SDK

– AMD APP SDK 2.4 released April 2011, fully conformant with

OpenCL 1.1, includes CPU support

– OpenCL support initially added for SandyBridge

– Released fully conformant OpenCL 1.1 SDK Beta May, 2011

– GPU first supported on CUDA platform

– OpenCL 1.0 support ships with production drivers


OpenCL | Code Sample

Think C99, Minus

– recursion

– function pointers

– variable-length arrays

But With

+ Math functions (matrix / vector)

+ extensions for

“work item” support

Vector, Image types

+ Image manipulation ops (AMD)

+ H.264 encode (Intel)

OCL Kernel:

workspace = (img_width, img_height)

__constant sampler_t sampler = CLK_ADDRESS_CLAMP |

CLK_FILTER_NEAREST | CLK_NORMALIZED_COORD_FALSE;

__kernel void RGBA2GRAY(__read_only image2d_t RGBAImg,

__write_only image2d_t GrayImg)

{

int2 coord;

coord.x = get_global_id(0);

coord.y = get_global_id(1);

uint4 rgba = read_imageui(RGBAImg, sampler, coord);

float4 frgba = convert_float4(rgba);

float4 coef = (0.299f,0.587f,0.114f,0.0f);

float res = dot(frgba, coef);

uint res_int = round(res);

uint4 res_vector = (res_int, res_int, res_int, res_int);

write_imageui(GrayImg, coord, res_vector);

}


OpenCL | Drawbacks and Challenges

DRAWBACKS

– Not quite C or C++

– Hardware-specific “Tweaking” required

– (Potentially) requires 4 or more code streams to maximize performance

CHALLENGES

– Initial implementation costs

– Code complexity

– Support costs

– Install package complexity


SO WHY USE GPU / OpenCL?


VIDEO STUDIO X4 – Software vs OpenCL Encode

The Treasure Hunters

Clip Length: 199 Seconds

OpenCL Encode

137.5 Seconds

69% of realtime

Software Encode

322.4 Seconds

162% of realtime

OS: Windows 7 64-bit Ultimate

CPU: AMD PhenomII X6 1055T 2.8GHz

VGA: AMD Radeon HD 6870

Memory: 4.00GB


OpenCL | In the future

Transparent data and kernel switching between devices (CPU and GPU)

Operation of kernels on CPU or GPU without re-compilation

Corel’s Wishlist:

– Speedy transition of extensions to core OpenCL spec

– IHV alignment on rapidly moving OpenCL forward

– Continued focus on C99 “Likeness”

– Focus on tools by all IHV’s


COREL’S VIEW OF

OPTIMIZATION


COREL | A brief history

Entrepreneur start-up

Products over 26y history:

– Laser printers, SCSI cards

– CorelDRAW grew out of an extension to a DTP product

– Desktop Video Conferencing

– Linux OS

– 100’s of Windows Apps – many from acquisitions

Private / Public / Private / Public / Private(!) ownership

= Adept at change management!


WITH CREDIT TO WINSTON CHURCHILL

CHURCHILL:

COREL:

“Study History, study

history. In history lies all

the secrets of statecraft”.

Study History, study

history. In history lies all

the secrets of statecraft

optimization!


TOP 3 TAKEAWAYS:


TOP 3 TAKEAWAYS:

TAKE POST-MORTEM’S SERIOUSLY, AND

IMPLEMENT PROCESS CHANGES


TOP 3 TAKEAWAYS:



COMMIT TO KEY STAFF


TOP 3 TAKEAWAYS:



COMMIT TO KEY STAFF

“OPTIMIZATION SHOULD BE

ALL ABOUT THE USER”


CASE STUDY | CorelDRAW 7

“IT’S ALL ABOUT THE USER”

Success: Where optimization was focused on our users:

– “Real-Time” editing in CorelDRAW

– Increased battery life in WinDVD

Failure : Where it was not:

– Re-architecture / optimization not focuses on explicit user benefit


FOR OPTIMIZATION, IT’S

REALLY

ALL ABOUT THE USER



Test Image

500 objects, 2,000 points

Optimization Result:

– Display speed increased 10x

Engineer’s Test Drawing



Validation: Image

9 x 568 objects, 9 x 3,888 points

Optimization Result:

– Display speed increased 10x



Litmus Test:

6,254 objects, 52,378 points

Before Optimization:

– Display time ~2 minutes



Litmus Test:

6,254 objects, 52,378 points

Before Optimization:

– Display time ~2 minutes

After Optimization:

– Display time ~90 sec



What Happened?

Good News: In the end, “The Huntress” achieved the same 10x speed-up, displaying in about 10 seconds

Cause of discrepancy:

– Train creator used nested hierarchy of objects

– Huntress creator used linear object list



What Happened?

Good News: In the end, “The Huntress” achieved the same 10x speed-up, displaying in about 10 seconds

Cause of discrepancy:

– Train creator used nested hierarchy of objects

– Huntress creator used linear object list

KEY TAKEAWAY: Without knowing all user scenarios, can’t predict bottlenecks


CASE STUDY | …AND CorelDRAW X5

Only 429 Objects, 25,061 Points

– but mesh fills = a new bottleneck!


SO:

“WHY OpenCL?”


TRENDS IN DIGITAL MEDIA – COREL’S VIEWPOINT

Trend User Impact Enhanced by OpenCL*

GPU & CPU advances More processing power

Mobile Computing More data on the cloud

Social Networking More cloud-based fix & edit

Touch-Based UI’sIncreased demand for

instant feedback

More 3D More data to process

Streaming Video Processing time extends wait

Enhanced User experience Rising user expectations

*Corel’s current optimization plans – does not reflect general OpenCL applicability


WHAT MATTERS TO OUR DIGITAL MEDIA USERS? | Many Variables

Open / Save Speed

Rendering / Encoding Speed

Battery Life

Execution of operations:

– Real-time preview of effects

– Image correction operations


PaintShop Pro – Original Image


PaintShop Pro – 3 Clicks / 30 seconds later

- Straighten

- Smart Photo Fix

- Local Tone Map


GUIDING OPTIMIZATION DECISIONS

Corel’s approach: Employ a framework to guide optimization decisions

Case Study: VideoStudio Encoding Optimization

– Data Flow Block Diagram

– Stated Objectives / desired outcomes (from PM / UED)

– Decision Tree (backed by detailed spreadsheet)


Case Study: Data Flow Block Diagram – Encoding / Rendering in VideoStudio

Original

File(s)Encoded

File

CPU

Decoding

CPU Video Render

(effect / composite /

scaling / de-interlace

/ color conversion)

CPU

Encoding /

Mixing

GPU

Decoding

DXVA Accel

GPU/D3D Video

Render (effect /

composite / scaling /

de-interlace / color

conversion)

GPU Encoding

(H.264 / MPEG 2)

Legend

System Memory transfer

System/Video Memory Transfer

Video Memory Transfer


Case Study: Clearly Stated Objectives

Clarity around optimization objectives from the user’s perspective is a key input

Some examples:

– Decrease time-to-render on target platforms by 50%, and ensure all platforms are at least 10% faster

– Make the XYZ effect real-time for any platform that meets our minimum spec

– Etc.


Request for

Performance

Improvement

Proceed with

Design/Native

Code optimization

Design & Code

currently optimized

in C / C++?

Can the data

or operation be

parallelized?

Is the

operation

relative easy to

implement in

“standard”

OpenCL?

Provide 2 or more

implementations, based

upon hardware

Proceed with OpenCL

implementation

Implement on latest

version of OpenCL

Focus on CPU

Based optimization*

Implement on latest

Common version of

OpenCL

Implement solutions

Optimized by HW

Proceed witn

Non-OpenCL

implementation

YES

NO

Will optimized

Design / Native

Code address

Needs?

Is the

req’d functtionality

Available in 1 or more

external proprietary

libraries?

Performance

critical area, or risk/

QA effort warrant

using extension /

library?

Does

performance

difference warrant

splitting code

paths?

At least one

Solution using

OpenCL

Is the

latest

version of OpenCL

supported on all

req`d HW

NO

NO

YES

YES

NO

YES NO NO YES

YES YES NO

NO

YES

YES

Case Study: Encode Path Decision Tree


Can the data

or operation be

parallelized?

YES

NO

Parallelism will usually be a key decision for OpenCL usage;

however, exceptions always exist (for example, when battery usage is critical)

Focus on CPU

Based optimization*




Provide 2 or more

implementations, based

upon hardware

Proceed with OpenCL

implementation

Performance

critical area, or dev

risk warrants

using extension /

library?

YES

NO

Maintaining a single code base will always be preferable,

but performance will sometimes warrant forking the code



Implement on latest

version of OpenCL

Is the

latest

version of OpenCL

supported on all

req`d HW?

YES

NO

Developers will usually push to use the latest / greatest version of any technology,

but that may not be the correct answer for our users


Case Study: Reminder

This is one of the VideoStudio decision trees

– Helps to focus where efforts should be directed for one class of optimization

Other apps or workflows will have their own decision tree’s

Presentation materials will be shared online


CLOSING CTO MUSINGS

Post Mortems are good – in-process checklists, prepared in advance, are better!

Objectives Checklist Check

Optimizing on features that matter to users?

Battery performance, Open/save, rendering, encoding, other

Positive impact on largest/most important group of users?

Is OpenCL the right tool?

Options – OpenCL kernel libraries (e.g. AML), optimize existing code,

existing design

What’s changed?

Availability of technology or support for it

Are we keeping a reference copy of code to validate results?

Are we comparison checking results?

Did we validate results with real user artifacts AND real users?


CLOSING CTO MUSINGS – CONT’D

Post Mortems are good – in-process checklists, prepared in advance, are better…

….. And hardware vendors collaborating to progress OpenCL is great!


THANK YOU!


Presentation Back-up Materials

Corel Stop Motion Video: Treasure Hunters

http://vimeo.com/20610210

http://youtu.be/xFDs-_CJHm8

Corel Stop Motion Secrets: Meet the Filmmaker (interview with John Huang)


http://youtu.be/6zwO8Pp--WQ

Corel Time-Lapse Video: Time in Motion:


http://youtu.be/hHvmiLpIsIY

Additional movies by two WordPerfect Project Leaders.

http://www.truedimensions.com/timesage/movies.htm










http://youtu.be/hHvmiLpIsIY

http://www.truedimensions.com/timesage/movies.htm

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