Please help somebody regarding this..Why is parallel execution time is coming more than sequential code given here..

Question

0.00/5 (No votes)

See more:

Parallel execution time is more than sequential code.(Code has been executed on dual core processor.)
Why is it so??

First run this, then comment the parallel code & uncomment sequential code, then again run it & check both the run times.

C#

/*****NOTICE:- Please do not run both, sequential & parallel codes together**/

     /*******Code for sequentially Finding largest in 2-d MATRIX***
            var sw = Stopwatch.StartNew();
            int[,] a = { { 3, 1, 2 }, { 5, 4, 6 }, { 2, 3, 4 }, { 5, 9, 1 } };
            int t = 0;
            for (int i = 0; i < 4; i++)
            {
                for (int j = 0; j < 3; j++)
                {
                    if (t < a[i, j])
                    {
                        t = a[i, j];
                    }
                }
            }
            Console.WriteLine("Largest element = " + t);
      ****END of sequential code********/

            /*******Parallel START of Finding largest in 2-d MATRIX******/
                    int[,] a = { { 3, 1, 2 }, { 5, 4, 6 }, { 2, 5, 4 } ,{5,9,1}};

                    var sw = Stopwatch.StartNew();
                    int[] t = new int[4];
                    Parallel.For(0, 4, (int i) =>
                        {
                            t[i] = a[i, 0];
                            for (int j = 1; j < 3; j++)
                            {
                                if (t[i] < a[i,j])
                                {
                                    t[i] = a[i,j];
                                }
                            }
                        }
                        );
                    int x = t[0];
                    for (int j = 1; j < t.Length; j++)
                    {
                        if (x < t[j])
                        {
                            x = t[j];
                        }
                    }
                    Console.WriteLine("Largest no. = " + x);

        /********END of Finding largest in 2-d MATRIX**********/




            TimeSpan s = sw.Elapsed;                    // For calculation
            Console.WriteLine("Run time = " + s);     // of timespan

            Console.ReadLine();

[edit]SHOUTING removed - OriginalGriff[/edit]

Posted 22-Sep-11 7:44am

Ratika Agarwal

Updated 24-Sep-11 20:08pm

v7

Add a Solution

Comments

OriginalGriff 22-Sep-11 14:11pm

DON'T SHOUT. Using all capitals is considered shouting on the internet, and rude (using all lower case is considered childish). Use proper capitalisation if you want to be taken seriously.

Ratika Agarwal 22-Sep-11 14:14pm

ok. thanks.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2011-09-22T08:17:00

Solution 1

I'm not surprised: there is a both an extra loop in the parallel version:

C#

for (int j = 1; j < t.Length; j++)
{
    if (x < t[j])
    {
        x = t[j];
    }
}

And the parallel portion is only four iterations and there is the extra thread startup overhead on top.

Depending on the number of cores you have, and the other activity of the system, you may (or may not) get any real parallel processing - it could end up as sequential on the same core if no other cores are available to take the load.

Posted 22-Sep-11 8:17am

OriginalGriff

Comments

Ratika Agarwal 22-Sep-11 15:14pm

Now check the following code.
There is change only in parallel version loop. But then also the time concept is opposite.

int[,] a = { { 3, 1, 2 }, { 5, 4, 6 }, { 2, 5, 4 }, { 5, 9, 1 } };
var sw = Stopwatch.StartNew();
int[] t = new int[4];

/**********************Parallel code START of Finding largest in 2-d MATRIX***********
Parallel.For(0, 4, (int i) =>
{
t[i] = a[i, 0];
for (int j = 1; j < 3; j++)
{
if (t[i] < a[i,j])
{
t[i] = a[i,j];
}
}
Console.WriteLine("Largest no.t["+i+"] is = " + t[i]);
}
);
int x = t[0];
for (int j = 1; j < t.Length; j++)
{
if (x < t[j])
{
x = t[j];
}
}
Console.WriteLine("Largest no. = " + x);
********************END of Finding largest in 2-d MATRIX*******************/

/***************Sequentially Finding largest in 2-d MATRIX***/
int i;
for (i = 0; i < 4; i++)
{
t[i] = a[i, 0];
for (int j = 1; j < 3; j++)
{
if (t[i] < a[i, j])
{
t[i] = a[i, j];
}
}
Console.WriteLine("Largest no.t["+i+"] is = " + t[i]);
}
int x = t[0];
for (int j = 1; j < t.Length; j++)
{
if (x < t[j])
{
x = t[j];
}
}
Console.WriteLine("Largest element = " + x);

TimeSpan s = sw.Elapsed; // For calculation
Console.WriteLine("total time = " + s); // of timespan

Console.ReadLine();

Ratika Agarwal 24-Sep-11 11:09am

anybody please answer