09 intel v_tune_session_13

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Code Optimization and Performance Tuning Using Intel VTune

In this session, you will learn to:

Identify the benefits of multithreading

Design applications using threads

Objectives

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Multithreading increases the performance of your application by:

Performing multiple tasks in parallel

Better utilization of system resources

Increasing the speed of your application

Identifying the Benefits of Multithreading

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Thread is a sequential flow of control within a program.

It is a sequence of instructions executed within a program.

Every program consists of at least one thread, called the

main thread.

The main thread is responsible for initializing the programs.

Identifying the Benefits of Multithreading (Contd.)

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What is a thread?

Just a minute

Answer:

A thread is a sequential flow of control within a program.

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The main benefits of threads are:

Increased performance

Better resource utilization

Simpler communication


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The two inherent conditions of a multithreaded application

are:

Concurrency

Parallelism


Concurrency refers to a situation in

which one or more threads are in

progress simultaneously.

In this case, the processor switches

from one thread to another during the

execution of the application.

►Parallelism refers to the simultaneous

execution of multiple tasks.

In a multithreaded application, which is

running on a multiprocessor system,

threads execute in parallel.

►

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The best time for threading an application is during its

design phase.

During the design phase, you can accommodate all the data

and code restructuring related to threading.

This reduces the overall effort during the application

development.

A program comprising of multiple independent activities can

be redesigned in such a manner so that each activity can

be defined as a separate thread.

This enables you to decompose your work into simple

independent activities and improve the functionality and

performance of your application.

Designing Applications Using Threads

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You can improve the functionality of your application by

assigning different threads to different functions of the

application.

By assigning a separate thread to each function, all the

functions can execute independent of each other.

This approach makes the application more efficient because

threading is easier than switching functions within a serial

code.

Designing Applications Using Threads (Contd.)

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Performance of an application depends upon the

combination of various factors such as speed and utilization

of system resources.

A multithreaded application running on a single processor

system leads to a better utilization of system resources.

A multithreaded application running on a multiprocessor

system leads to better utilization of system resources and

increased speed of the application.


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How does the use of threads improve the functionality of an

application?

Just a minute

Answer:

Threads improve the functionality of an application by

assigning different threads to different functions. This makes it

easier to control the execution of multiple functions within an

application.

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Data decomposition refers to the process of:

Breaking down a program into logical chunks or individual

tasks.

Identifying the dependencies between the tasks.

The two types of decomposition methods are:

Task decomposition

Data decomposition


► It refers to the process of decomposing

a program on the basis of the functions

it performs.

It is also known as functional

decomposition.

In this case, you can assign separate

threads to the independent functions in

your program.

► It refers to the process of decomposing

an application in such a way so that the

same operation is performed repeatedly

for different data.

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In a multithreaded application, you need to take care of

various complexities, which may arise during thread

interaction. These complexities are:

Race conditions

Critical region

Mutual exclusion

Synchronization

Deadlocks

Identifying the Complexities Involved in Multithreaded Applications

► Race conditions occur when the output

of the program depends upon which

thread reaches a particular block of

code first.

Race conditions lead to different

results every time a program is

executed.

► Critical region refers to those portions

of your application that access shared

variables.► Mutual exclusion allows only one

thread to be executing in a critical

region at a given time.

When a thread is executing the code

that accesses a shared resource in a

critical region, any other thread that

might desire entry to the critical region

must wait to access that region.

► Synchronization controls the relative

order of thread execution and resolves

any conflicts among threads.

Synchronization is based on the

concept of monitoring.

► Deadlock refers to a situation in which

a thread waits for a condition that can

never occur.

Deadlock halts the execution of your

application preventing it to continue

further.

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List the complexities involved in a multithreaded application.

Just a minute

Answer:

The complexities involved in a multithreaded application are as

follows:

Race conditions

Critical region

Mutual exclusion

Synchronization

Deadlocks

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Problem Statement:

John has developed a code in C# in which he acquires a lock on two resources. However on execution, the application comes to a halt after some time. He wants to analyze the processor utilization on his system using the counter monitor feature of VTune. Help John to accomplish his task.

Activity: Analyzing the Processor Activity During Deadlock

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Solution

To analyze the performance of the application, you need to perform the following tasks:

1. Configure counter monitor using the counter monitor configuration wizard.

2. Analyze the processor utilization on the system.

Activity: Analyzing the Processor Activity During Deadlock (Contd.)

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In this session, you learned that:

You can improve the speed of your application to a great extent

by using multiple threads in your application.

A thread is a sequential flow of control within a program.

The main benefits of threads are as follows:

Increased performance

Better resource utilization

Simpler communication

In a multithreaded application, threads run concurrently or in

parallel.

You can improve the functionality of your application by

assigning different threads to different functions of the

application. These functions may or may not be dependant on

each other.

Summary

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The threads enable you to improve the performance of your

application.

The process of breaking down a program into logical chunks or

individual tasks and identifying the dependencies between

them is referred to as decomposition.

In a multithreaded application, you need to take care of various

complexities that may arise during thread interaction. These

complexities are as follows:

Race condition

Critical region

Mutual exclusion

Synchronization

Deadlock

Summary (Contd.)

Education

09 intel v_tune_session_13