On 23 March 2010 09:09, Andreas Raab <andreas.raab at gmx.de> wrote:
> On 3/22/2010 9:21 PM, Andreas Raab wrote:
>>>
>>> Also, I was under the impression that Alien FFI was faster than the
>>> standard FFI.
>>
>> Oh, dear. This is hearsay, right? I.e., neither you nor anyone who
>> claims it have ever ever run an actual benchmark, have you?
>
> I thought it'd be fun to make a little benchmark so here we go. I'm using
> the most trivial example, namely the call to glGetError() which should be
> done early and often :-) Using the FFI (from CroquetGL) this looks like
> here:
>
>        ogl := OpenGL newIn: (0 at 0 corner: 10 at 10).
>        time := [1 to: 1000000 do:[:i| ogl glGetError]] timeToRun.
>        ogl destroy.
>
> This takes about 435 msecs. Now the same with AlienOpenGL in Pharo:
>
>        drawable := OpenGLSurface newIn: (0 at 0 corner: 10 at 10).
>        ogl := AlienOpenGLLibrary uniqueInstance.
>        time := [1 to: 1000000 do:[:i| ogl glGetError]] timeToRun.
>        drawable close.
>
> This takes 8372 msecs. Whoopsie. That's a factor of 20x AlienOpenGL is
> slower for the same C call. But okay, that may not be a fair comparison due
> to the naive use of Alien. Let's be more clever, look up the method just
> once and invoke it:
>
>        drawable := OpenGLSurface newIn: (0 at 0 corner: 10 at 10).
>        ogl := AlienOpenGLLibrary uniqueInstance.
>        alienMethod := ogl alienMethodNamed: 'glGetError'.
>        time := [1 to: 1000000 do:[:i|
>                error := GLEnum new.
>                alienMethod primFFICallResult: error.
>        ]] timeToRun.
>        drawable close.
>
i don't know how to load this code, could you put
error := GLEnum new. out of block and run it again?

> This still takes 3589 msecs. Whoops, it did it again. Even with the more
> elaborate use Alien is still 8x slower than the FFI. That's the cost of
> doing marshalling in Squeak and the effect it has on Alien performance when
> compared with the FFI.
>
It is expected to see that marshalling/converting types takes most of the time,
while rest should be same, because it straightforward: push arguments,
make a call and return result.
So, at some cases (not at all), one could prepare arguments and return
value holder and then use it
in calls, avoiding allocating & converting them each time.
For instance, when you passing a string (char*),
one may use a CString object (a null-terminated String), and pass it
into Alien without conversion,
while FFI allocates a null-terminated strings on heap, copying String
contents to that buffer and then using them as arguments to a
function.
So its hard to say, which way is better.

> Cheers,
>  - Andreas

-- 
Best regards,
Igor Stasenko AKA sig.