performance issues

Programming Questions

Chrisir

in Programming Questions • 1 year ago

hello all,

I have performance issues within a for-loop that lies in a recursion.

Can I just ask some questions?

I learned while searching for "performance" in the forum the compiler is pretty bright and makes good decisions.
Obviously, I declare everything outside loop and recursion to save it time.

1st question: Does the data type make a difference in terms of speed?

Let's say

PVector []

versus

int[] // for x (or float)
int[] // for y
int[] // for z

or say

PVector []

versus

MyOwnClass[]

Any difference?

2nd question: Does the usage of Strings and + need a lot of time?

I heard usage of + with String is not recommended - what does the merging with StringBuilder look like?

3rd question: Allocated memory?

When I make the memory usage higher in my IDE and compile, does the exe-file (the application) under Win 64 knows the higher memory usage? Or how can I enforce it? (or doesn't it matter since Win 7 provides memory dynamically?)

4th question: Are there other pitfalls?

What are other pit falls?

Thank you!

Greetings, Chrisir

P.S.
I am referring to this beast, namely to tab Game2
(doesn't run in browser)
http://www.openprocessing.org/sketch/65645

Replies(13)

benja

Re: performance issues

1 year ago

Hey,

without looking into your code yet.
1. It makes a difference, using three int-arrays is faster than using PVector, but i think it only matters if you have lots of iterations. I can't imagine, why there should be a differnce in performance between PVector and your own classes.

2. concat() is about twice as fast as combining strings with "+=".
But the differnce when using StringBuilder is huge. An example:

String message = "";
int num = 10000;

int t = millis();
for (int i = 0; i< num ; i++) {
message += "b";
}
println("'+=' : "+(millis()-t));

message="";
t = millis();
for (int i = 0; i< num ; i++) {
message = message.concat("b");
}
println("concat(): "+(millis()-t));

t = millis();
StringBuilder sb = new StringBuilder();
for (int i = 0; i< num ; i++) {
sb.append("b");
}
message = sb.toString();
println("StringBuilder(): "+(millis()-t));

No ideas to 3. and 4. at the moment, but maybe i'll have a look into your example later.

Chrisir

Re: Re: performance issues

1 year ago

I was able to do the calculations now without any usage of String. And this gave a huge improvement on performance.

Thank you very much for pointing me to the fact that String can be problematic!

I am doing now everything via int[][][] and reduced that again to byte[][][].

Thanks!

Greetings, Chrisir

PhiLho

Re: performance issues

1 year ago

IIRC, the memory setting set in the PDE is exported, in the args.txt file.

Chrisir

Re: performance issues

1 year ago

That's great, thanks you to both!

In fact I don't need String at all, it could be all done via int[][][].

Anyway, it's a shame that arrayCopy or isEqual doesn't work for 3D arrays - I need to for-loop there as well.

Is % and join considered to be fast?

Thanks again!

Greetings, Chrisir

Chrisir

Re: performance issues

1 year ago

hello,

I am still struggling with this....

I need to do one thing fast :

compare two 3D arrays

is there a better was than to do a triple for-loop?

I was thinking of use concat to have the data of the 3D array in a 1D array and then use
join to have it as a string and then use .equals on the string - thus no need for a for-loop at all.
But how can I use concat to have the data of the 3D array in a 1D array?

Thanks a lot!

Chrisir

benja

Re: performance issues

1 year ago

Not sure if that is the fastest solution, but have you tried Arrays.deepEquals() ?

int[][][] a1 = new int[4][4][4];
int[][][] a2 = new int[4][4][4];

void setup() {
for (int i = 0; i< a1.length; i++) {
    for (int j = 0; j< a1[0].length; j++) {
      for (int k = 0; k< a1[0][0].length; k++) {
        a1[i][j][k] = 3;
        a2[i][j][k] = 3;
      }
    }
}
println(Arrays.deepEquals(a1, a2));
}

Chrisir

Re: performance issues

1 year ago

That was very helpful!

Thanks a lot!

Chrisir

Re: performance issues

1 year ago

hello,

sorry,

Another performance question from this program :

I'm using my own function arrayCopy3D (see below) with 2 for-loops to copy a 3D-Array.
To use = doesn't work because it copys only the adress in the memory. Not ok.
Is there a faster way such as deepCopy?

int[][][] arrayCopy3D ( int[][][] src )
{
int[][][] dest;
dest=new int [intConstEnd][intConstEnd][intConstEnd];
for (int j=0; j<src.length; j++) {
for (int i=0; i<src.length; i++) {
arraycopy(src[j][i], dest[j][i]);
} // for
} // for
return dest;
} // func

Thanks!

Greetings,

Chrisir

Chrisir

Re: performance issues

1 year ago

Hello,

another question from working on this program:

I use several times pegs [i].x.

Would it be faster if I said

int x1= pegs [i].x;

and then only use x1 further on?

Thanks, Chrisir

PhiLho

Re: performance issues

1 year ago

Well, there might be a little performance gain, in theory... The difference might be hardly perceptible in a real sketch. And the Java compiler, or even the JIT compiler can even reduce the difference. Although only measurement can really tell. If you are passionate about these questions, look for the Caliper library, it can help you to answer these.

Note that another reason for writing the expression above is... it helps readability and can reduce typing!

Chrisir

Re: performance issues

1 year ago

Thank you very much!

Prokop Ha..

Re: performance issues

9 months ago

Hi,

I'm also interested in speed of PVector class because I use it for many-body simulation such as molecular dynamics ( http://en.wikipedia.org/wiki/Molecular_dynamics) or mechanics of truss ( http://en.wikipedia.org/wiki/Truss )

I just made some test of performance where i propagate 10^7 - 10^8 iteration of dynamics of 3D harmonic oscillator by different methods:

"float" - everything is computed explicitly in floats
"PVector1" - uning PVectors, global temporary PVector "temp" is used to avoid creation of new objects
"PVector2" - using PVectors in naive way ( new objects are crated in operations like PVector.mult(k,x) )
"MyVector" - I made class similar to PVector however with operations like addmult and setmult to avoid creation of new objects or copying to global temporary object

Result of the test:

time taken by 10^7 iterations
float 219.0 ms
MyVector 313.0 ms
PVector1 437.0 ms
PVector2 719.0 ms
time taken by 10^8
float 2187.0 ms
MyVector 3079.0 ms
PVector1 4516.0 ms
PVector2 7406.0 ms

Code of the methods:

"float" method

void move( ){
vx-=dt*fx/m; vy-=dt*fy/m; vz-=dt*fz/m;
x+=vx*dt; y+=vy*dt; z+=vz*dt;
}
void force( ){
fx=kx*x; fy=ky*y; fz=kz*z;
}

"MyVector" method

void move( ){
v.addmult( f, -dt/m );
x.addmult( v, dt );
}
void force(){
f.setmult( k, x );
}

"PVector1" method

void move( ){
temp.set(f); temp.mult(-dt/m); v.add(temp);
temp.set(v); temp.mult(dt); x.add(temp);
}
void force(){
f.set(x); f.mult(k);
}

"PVector2" method

void move( ){
v.add( PVector.mult( f, -dt/m ) );
x.add( PVector.mult(v,dt) );
}
void force(){
f.set( PVector.mult(k,x) );
}

My Conclusion:

The difference is smaller than I thought, the most stupid way (PVector2) is just 3-times slower than the fastest "float" version
Would be nice to have composed operations as "addmult" in PVector class, not just because of speed, but also because of readability and simplicity of code
If PVector would use fused multiply–add (FMA) or fused multiply–accumulate (FMAC) and SSE vector operations it would be probably even faster than "float" method

Ale_

Re: performance issues

9 months ago

This thread is full of interest in every post. Thanks to everyone!

Ale · http://60rpm.tv/i

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