Anyway, to speed up this feature?

I have a voxel (minecraft style) engine in XNA, the world is divided into pieces, and when the cube is changed, I update the vertex buffer by looking at all the cubes and checking if the faces are visible. This usually works at a good speed, but when the cubes are arranged in a certain way (so that the vertex buffer will be much larger), it can capture a frame to create a new fragment. In the worst possible configuration (indicating the most possible vertices), it can take up to 100 ms. The next part of the code is about 80-90 ms 100, and when updating the fragment, it executed 131,072 times, with the worst possible configuration, it creates 32,768 cubes, and on all other starts it creates 0 vertices.

I am also on the i5 2500k, so on older systems this can be very bad.

I can’t come up with to improve speed, and I'm pretty new to programming, so I thought I'd post it here for some tips? Thank.

public void GenerateCubeGeometryAtPosition(int x, int y, int z, byte id)
{
    //We check if there a cube in the six directions around the cube
    //if there no cube ot the cube is transparent we add the vertices to the vertex list
    //if the cube is on the outside of the chunk we check the cube in the chunk next to it assuming it loaded

    //if we have to build part of the cube we make a new vertex
    //first 3 bytes in the vertex are the position relative to the chunk
    //4th byte is for normals, we check it in the shader to figure out the normal
    //the next 2 bytes in the properties are for the texture positons on the texture atlas
    //last 2 bytes are for other properties of the vertex like light/shade etc

    //Check up and down
    if (y > YSize - 2)
    {
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, 1 + z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[3]));
    }
    else if (Blocks[x, y + 1, z] == 0 || GlobalWorld.Blocks[Blocks[x, y + 1, z]].Transparent)
    {
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, 1 + z, 0f), GlobalWorld.Blocks[id].VertexPropertiesTop[3]));

    }
    if (y != 0 && (Blocks[x, y - 1, z] == 0 || GlobalWorld.Blocks[Blocks[x, y - 1, z]].Transparent))
    {
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, z, 1f), GlobalWorld.Blocks[id].VertexPropertiesBottom[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, 1 + z, 1f), GlobalWorld.Blocks[id].VertexPropertiesBottom[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, z, 1f), GlobalWorld.Blocks[id].VertexPropertiesBottom[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, 1 + z, 1f), GlobalWorld.Blocks[id].VertexPropertiesBottom[3]));
    }

    //check Right and Left of the cube and the adjacent chunk at the edges
    if (x == 0)
    {
        if (this.RightChunk != -1 && (GlobalWorld.LoadedChunks[this.RightChunk].Blocks[XSize - 1, y, z] == 0 || GlobalWorld.Blocks[GlobalWorld.LoadedChunks[this.RightChunk].Blocks[XSize - 1, y, z]].Transparent))
        {
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[0]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[1]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, 1 + z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[2]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[3]));
        }
    }
    else if (Blocks[x - 1, y, z] == 0 || GlobalWorld.Blocks[Blocks[x - 1, y, z]].Transparent)
    {
        //right
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, 1 + z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 3f), GlobalWorld.Blocks[id].VertexPropertiesRight[3]));
    }
    if (x > XSize - 2)
    {
        if (this.LeftChunk != -1 && (GlobalWorld.LoadedChunks[this.LeftChunk].Blocks[0, y, z] == 0 || GlobalWorld.Blocks[GlobalWorld.LoadedChunks[this.LeftChunk].Blocks[0, y, z]].Transparent))
        {
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[0]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, 1 + z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[1]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, 1 + y, z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[2]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, 1 + y, 1 + z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[3]));
        }
    }
    else if (Blocks[x + 1, y, z] == 0 || GlobalWorld.Blocks[Blocks[x + 1, y, z]].Transparent)
    {
        //left
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, 1 + z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, 1 + y, z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, 1 + y, 1 + z, 2f), GlobalWorld.Blocks[id].VertexPropertiesLeft[3]));
    }

    //check Back and Front of the cube and the adjacent chunk at the edges
    if (z == 0)
    {
        if (this.BackChunk != -1 && (GlobalWorld.LoadedChunks[this.BackChunk].Blocks[x, y, ZSize - 1] == 0 || GlobalWorld.Blocks[GlobalWorld.LoadedChunks[this.BackChunk].Blocks[x, y, ZSize - 1]].Transparent))
        {
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[0]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[1]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[2]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[3]));
        }
    }
    else if (Blocks[x, y, z - 1] == 0 || GlobalWorld.Blocks[Blocks[x, y, z - 1]].Transparent)
    {
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, z, 5f), GlobalWorld.Blocks[id].VertexPropertiesBack[3]));
    }
    if (z > ZSize - 2)
    {
        if (this.ForwardChunk != -1 && (GlobalWorld.LoadedChunks[this.ForwardChunk].Blocks[x, y, 0] == 0 || GlobalWorld.Blocks[GlobalWorld.LoadedChunks[this.ForwardChunk].Blocks[x, y, 0]].Transparent))
        {
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[0]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[1]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[2]));
            ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[3]));
        }
    }
    else if (Blocks[x, y, z + 1] == 0 || GlobalWorld.Blocks[Blocks[x, y, z + 1]].Transparent)
    {
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[0]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(x, y + 1, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[1]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[2]));
        ChunkVertices.Add(new VertexPositionNormalSmall(new Byte4(1 + x, y + 1, 1 + z, 4f), GlobalWorld.Blocks[id].VertexPropertiesFront[3]));
    }
}