[Mono-dev] Jagged arrays over multidimensional arrays

[Rodrigo Kumpera]

Your code is testing two things.
First GC performance, which mono lags behind but work on this is ramping up
fast.
Second arrays bound elimination, which we don't perform by default.

Running your code with -Oabcrem might improve things.


On Tue, Mar 24, 2009 at 11:53 AM, Stifu <stifu at free.fr> wrote:

>
> Microsoft (through MSDN and FxCop) recommends using jagged arrays
> (likeThis[][]) over multidimensional arrays(likeThat[,]), because they're
> usually faster, basically (especially if the sub arrays in your jagged
> array
> don't all have the same size). See:
> http://msdn.microsoft.com/en-us/library/ms182277.aspx
>
> I made a simple test program that initializes arrays to check the speed
> difference, and I could see that with a simple initialization loop, jagged
> arrays were indeed a bit faster than multidimensional ones (even if all sub
> arrays in the jagged array have the same size, as with a multidimensional
> one).
>
> But before changing all the multidimensional arrays to jagged arrays in my
> application, I thought I'd check Mono... with which jagged arrays are
> slower
> than multidimensional ones, unlike with .NET.
>
> Is it worth filing a bug report for a performance issue like this one?
>
> For more details on the way .NET generates code for jagged and
> multidimensional arrays:
>
> http://www.guidanceshare.com/wiki/.NET_2.0_Performance_Guidelines_-_Arrays#Use_Jagged_Arrays_Instead_of_Multidimensional_Arrays
>
> About the tests I ran on my computer:
>
> .NET (2.0) results:
> Multidimensional arrays: 02.89 seconds
> Jagged arrays: 02.74 seconds
>
> Mono (2.4 RC3) results:
> Multidimensional arrays: 04.57 seconds
> Jagged arrays: 04.94 seconds
>
> And here's the test program (feel free to raise the "iterations" value, I
> set it to only 3000 because my computer is quite old):
>
> using System;
> using System.Windows.Forms;
>
> namespace Arrays
> {
>        public partial class MainForm : Form
>        {
>                public MainForm()
>                {
>                        InitializeComponent();
>
>                        int iterations = 3000;
>
>                        DateTime start = DateTime.Now;
>                        for(int i = 0; i < iterations; i++)
>                        {
>                                int[,] multiDimensionalArray = new int[128,
> 128];
>
>                                for(int y = 0; y < 128; y++)
>                                {
>                                        for(int x = 0; x < 128; x++)
>                                        {
>                                                multiDimensionalArray[y, x]
> = 5;
>                                        }
>                                }
>                        }
>                        TimeSpan duration = DateTime.Now - start;
>
>                        start = DateTime.Now;
>                        for(int i = 0; i < iterations; i++)
>                        {
>                                int[][] jaggedArray = new int[128][];
>
>                                for(int y = 0; y < 128; y++)
>                                {
>                                        jaggedArray[y] = new int[128];
>
>                                        for(int x = 0; x < 128; x++)
>                                        {
>                                                jaggedArray[y][x] = 5;
>                                        }
>                                }
>                        }
>                        TimeSpan duration2 = DateTime.Now - start;
>
>                        MessageBox.Show(String.Format(
>                                "Multidimensional array : {0}\n" +
>                                "Jagged array : {1}",
>                                duration.ToString(),
>                                duration2.ToString()));
>                }
>        }
> }
> --
> View this message in context:
> http://www.nabble.com/Jagged-arrays-over-multidimensional-arrays-tp22682187p22682187.html
> Sent from the Mono - Dev mailing list archive at Nabble.com.
>
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>
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