[Mono-dev] Mono SIMD Function Declarations and Timing

crashfourit crashfourit at gmail.com
Thu Nov 20 22:47:18 EST 2008

JTalton wrote:
> Hello,
> I wrote a small model editor called Golem3D.  Coded in C#, it uses OpenTK
> for rendering using OpenGL.  I helped with some of the math library for
> OpenTK and performed timing tests on the different function declarations.
> Example:
>   5.80    public static Vector4D operator+ (Vector4D v1, Vector4D v2);
>   ----    static Vector4D Add(Vector4D v1, Vector4D v2);
>   5.50    static Vector4D Add(ref Vector4D v1, ref Vector4D v2);
>   ----    static void Add(Vector4D v1, Vector4D v2, out result);
>   1.17    static void Add(ref Vector4D v1, ref Vector4D v2, out result);
>   1.25    void Add(Vector4D v);
>   1.00    void Add(ref Vector4D v);
>   ----    void Add(Vector4D v, out Vector4D result);
>   ----    void Add(ref Vector4D v, out Vector4D result);
> It seems that most of the overhead is in the copying of the structure. 
> Directly modifying a vector and passing in arguments with ref was the
> fastest implementation.  (Tested on Windows with .NET)
> While passing by ref is faster, sometimes you want to be able to call
> "a.Add(new Vector(1,1,1,1))" which does not work with ref.  So I am of the
> opinion both declarations with parameters as ref and parameters without
> ref
> are needed.
> Sometimes you want to say "a = b + c".  In the tests, this was the slowest
> of all the declarations.  I do think it is beneficial to have when used in
> non-repetitive tasks.
> How is this affected by the SIMD?  It looks like the generated assembly
> from
> the PDC slides gets rid of much of overhead from the copying of structure. 
> So in the case of Mono, this may not be an issue.  If you run the same
> code
> under .NET (which currently does not have SIMD support), it would matter.
> I would like to see timing tests of the different declarations with and
> without SIMD.  Also I'm only showing the "Add" function here, and other
> functions may accelerate further with SIMD.
> Other Thoughts...
> It would be nice to have a Vector3f since when using OpenGL you send a
> buffer of Vectors and with Vector4f you have a third more data to send to
> the graphics card.  Not sure if this is doable, or if SIMD must work on a
> full 128 bits.
> I think I saw that SIMD only supported 128 bits, so a Vector of 3 doubles
> would not work.  Is there a way to make a Vector of 3 double or 4 doubles
> that uses two SIMD instructons? i.e. like a Vector4D was actually 2
> Vector2Ds? (I know there are some issues, but thoughts?)
> While it is nice to have Properties for the variables in the vector, it
> would be nice to have the variables exposed.  This is needed since calling
> into the OpenGL functions would work cleaner with GL.Normal3(ref
> vector.X).
> Matrices and Quaternions?  If matrices are implemented, I'd like to see
> them
> compatible with OpenGL's matrix format.
> Sorry if I covered anything that has been brought up before.  I searched
> all
> the SIMD threads and did not see any of this covered.
> I plan to get the SIMD accelerated library and test some things out when I
> find the time.  If there is anything I can do to help, from testing to
> reviewing interfaces to documentation, let me know.
> James
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Would you care to do the same tests on Mono and .Net using "class" instead
of "struct" to see what happens? It would be interesting to look at. Also,
include object creation in that as well. Thanks.
View this message in context: http://www.nabble.com/Mono-SIMD-Function-Declarations-and-Timing-tp20614041p20614778.html
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