game threading analysis & methodology · performance profile ai decomp. with 2 threads locks...

Game Threading Analysis & Methodology

Session:

SOFTWARE AND SERVICES Copyright © 2014, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. * Other brands and names are the property of their respective owners.

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Objectives

At the end of the module you will be able to: • Describe two strategies to parallelize a game using two different

threading implementations • Evaluate the effectiveness of each strategy with respect to how each

uses the underlying number of cores we WILL NOT be teaching you how to program using Windows API. We

will not be teaching you how to program with Threading Building blocks. We will not be teaching you how to program DirectX or Direct 3D.

This module is intended primarily to show a higher level method of

attack for games and how to use tools to evaluate the effectiveness of the threading strategy.


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Introduction to Intel® Parallel Amplifier

Usual Game Structure Parallelization with Windows* Threads

What is Intel® Threading Building Blocks?

Parallelization with

Intel® Threading Building Blocks

Curriculum Application & Summary

Agenda

* Intel and the Intel logo are registered trademarks of Intel Corporation. Other brands and names are the property of their respective owners.


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Motivation for a threading Tool

Developing efficient multithreaded applications is hard New performance problems are caused by the interaction between

concurrent threads • Load imbalance • Contention on synchronization objects • Threading overhead

Need a tool to help!


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Intel® Parallel Amplifier

• Component within the Intel® Parallel Studio • Has 3 main charters

• Identify hotpots in an application • Identify level of concurrency in an application • Identify locks & waits

• In this module, we will look specifically at locks & waits


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Amplifier Locks & waits - Synchronization View

Orange: OK – Acceptably utilized CPU cores

Red: Poor – Underutilized CPU cores

Synchronization Object View: This view shows the kinds of synchronization

objects and effects they are having on performance – Threads, Critical

Sections, etc identifies here

Green: Ideal – Fully utilized CPU cores

Blue: Over – Over -utilized CPU cores


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Amplifier Locks & waits – Wait Thread View

Wait Thread View: This shows the threads and functions that are waiting. It also depicts the relative proportion of app spent undersubscribed, fully subscribed or oversubscribed

Summary View: This shows a graph indicating how much time in app is spent fully subscribed to cores


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Concurrency Profile

Measure core utilization so user can see how parallel their program really is

• Relative to the system executing the application Idle: no active threads Under-subscribed: # threads > 1 && # threads < # cores OK: More than a single thread Fully-subscribed*: # threads == # cores Oversubscribed: # threads > # cores

Concurrency level is the number of threads that are active (not waiting, sleeping, blocked, etc.) at a given time

* example reflects 4 core machine


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Introduction to Intel® Parallel Amplifier Usual Game Structure Parallelization with Windows* Threads





Agenda



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Get Input Simulate Render

Usual Game Structure

http://softwarecommunity.intel.com/articles/eng/1363.htm

DTC uses the usual game loop

Get Input Physics AI Particles Render

Consists of loop called “Game Loop”

http://softwarecommunity.intel.com/articles/eng/1363.htm


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Lab Activity 1

Build Destroy the Castle • Follow the steps for Lab

Activity 1A & 1B in the student guide to build & run Destroy the Castle


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Limitation of Serial Games for Multi-Core Systems

With clock rates reaching into the multiple GHz range, further increases are becoming harder

Parallel hardware has gone mainstream for

desktop To exploit the performance potential of

multi-core processors, applications must be threaded

Serial games get no benefits from multi-core


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Parallelization with Windows* Threads


Parallelization with Intel® Threading Building Blocks


Agenda



Parallelization with Windows* Threads

Updating with double buffered data structures Decoupling rendering from frame processing Asynchronous update of parts of the scene Task Decomposition

Render

Physics

Particles

AI


ISC has 8 hour course on how to thread DTC with Windows* Threads

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Parallel Amplifier shows serial code dominating the execution

DTC Baseline Analysis

Locks & Waits for “Single Thread” run

Serial execution dominates

Terrible Frame Rate

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Performance Profile Task Decomposition

Locks & Waits for Multithreaded run

Thread pool for Render plus 3 “simulate” threads

Load balance issue Good frame rate

Some parallelism but … low utilization of 4 cores


Data Level Parallelism

Nested parallelism • Top level - task decomposition • Next level - data decomposition

update several AI units




Render

Physics

Particles

AI

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Lab Activity 2

Use Parallel Amplifier to Display Win version Baseline Locks & Waits Information

• Follow the steps for Lab Activity 2 in the student guide to analyze the baseline and Task Decomposition profiles you created in Activity 1


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Performance Profile AI Decomp. with 2 Threads

Locks & Waits for Multithreaded Plus 2 AI threads run

Better core utilization Best frame rate Starting to see

oversubscription Load balancing an issue

More parallelism … higher utilization of 4 cores


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Performance Profile AI Decomp. with 4 Threads

Locks & Waits for Multithreaded Plus 4 AI threads run

Oversubscription a problem

Load balancing issue Frame rate drops

Too many threads for number of cores


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One More Problem: Nested Parallelism

Software components are built from smaller components

If each turtle specifies threads...


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Disadvantages of …

Using Windows* and POSIX Threads for Games

• Low-Level details (not intuitive) – Hard to come up with good design – Code often becomes very dependent on a particular OS’s threading

facilities

• Load imbalance – Has to be managed manually

• Oversubscription – Multiple components create threads that compete for CPU resources – Hard to manage nested parallelism


Hard to achieve scalability


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Usual Game Structure Introduction to code instrumentation Parallelization with Windows* Threads





Agenda



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It is Open Source now! • http://www.intel.com/software/products/tbb/ • http://threadingbuildingblocks.org/ • Component in Intel Parallel Composer

Threading Abstraction Library • Relies on generic programming • Provides high-level generic implementation of parallel design

patterns and concurrent data structures You specify task patterns instead of threads

• Library maps your logical tasks onto physical threads, efficiently using cache and balancing load

• Full support for nested parallelism Targets threading for robust performance

• Designed to provide scalable performance for computationally intense portions of shrink-wrapped applications

• Portable across Linux*, Mac OS*, and Windows* Emphasizes scalable data parallel programming

• Solutions based on task decomposition usually do not scale * Intel and the Intel logo are registered trademarks of Intel Corporation. Other brands and names are the property of their respective owners.

http://www.intel.com/software/products/tbb/

http://threadingbuildingblocks.org/


Components of Intel® Threading Building Blocks

•Parallel algorithms •Concurrent containers •Synchronization primitives •Memory allocation •Task scheduler

Problem Intel® TBB Approach

•Low-Level details Operate with task patterns instead of threads

•Load imbalance Work-stealing balances load

•Oversubscription One scheduled thread per hardware thread

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Lab Activity 3

Build the TBB version of Destroy the Castle, collect profile data and then analyze the data to compare this parallel strategy to the previous one.


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Introduction to code instrumentation Parallelization with Windows* Threads





Agenda

* InteCul and the Intel logo are registered trademarks of Intel Corporation. Other brands and names are the property of their respective owners.


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Parallelization with TBB

Scheme of parallelization with Windows*

Render

Physics

Particles




. . .


update several blocks








update several particles




Render





Scheme of parallelization with Intel® TBB


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Task Graph

MainTask

AITask

AIBodyTask

AIFinalTask

Task creation order Task completion signals

AIBodyTask

AIBodyTask

SyncTask

PhysicsTask

ParticlesTask

Not expanded ...


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Performance Profile – MultiThreaded w AI run

Locks & Waits for Multithreaded TBB 2 extra AI tasks

Good frame rate Good Core utilization

Good utilization of 4 cores


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Limitation for Games

Intel® TBB is not intended for

– I/O bound processing – Hard real-time processing – Excessive usage of explicit synchronization

However, it is compatible with other threading packages – It can be used in concert with Windows* and POSIX threads, etc



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Advantages for Games

Generic Parallel Algorithms – You specify task patterns instead of threads – Cross-Platform implementation

Load balancing – Adaptive tuning to variable computation – Full support for nested parallelism

Efficient use of resources – One scheduled thread per hardware thread – Effective cache reuse

Easy to achieve scalability


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Lab Activity 4

Analyze the TBB version with Parallel Amplifier


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Introduction to code instrumentation Parallelization with Windows* Threads





Agenda



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Summary

Serial games get no benefits from multi-core

Analyzed two different parallelization strategies using core

utilization as a key metric Make you aware of some of the game threading related

materials we offer • including this 2 hour module, in addition to • 8 more hours covering game threading in depth – available

through the Intel Software College Academic community


Use this material in your Game or 3D Graphics curriculums now


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Call To Action

Think about Multi-Threading at the beginning of your project Think about scalable performance (for N cores, not just 2 or 4)

for years to come Plan now - how you can use this methodology in your

curriculum


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game threading analysis & methodology · performance profile ai decomp. with 2 threads locks...

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