[Openmcl-devel] OpenGL Performance PPC vs Intel-Mac 32/64

[R. Matthew Emerson]

On Mar 18, 2009, at 2:16 AM, Alexander Repenning wrote:

> Playing around with some direct mode (i.e., not super efficient)
> OpenGL code we notice some big speed differences:
>
> The time to draw a cube (4 sides only actually):
>
> 1.66 Ghz PPC Mac:   MCL 88 us,  CCL 1.3 60us
>
> 2.6 Ghz Intel Mac: CCL 1.3 32bit: 33us  CCL 1.3 64bit 92us
>
>
> I remember we had a discussion on PPC versus Intel call overhead but I
> am a bit surprised about 64bit Intel Mac CCL on a much faster machine,
> even ignoring the faster GPU, is slower than MCL on the old PPC.
> Notice, the OpenGL commands are pretty trivial. Most of the time is
> spent in the foreign function call overhead. How can CCL 32bit Intel
> Mac be  3x faster than 64bit ?

The first several paragraphs of the following message talk about this.

http://clozure.com/pipermail/openmcl-devel/2008-December/008766.html

In summary, due to missing functionality on Darwin/x8664 (no way to  
set the fsbase MSR) we resort to a workaround that involves performing  
a system call before and after each ff-call.  When the foreign  
function doesn't do a lot of work, this overhead is significant.   
(When the foreign code does something expensive, like I/O, the  
overhead matters less.)

On Darwin/x8632, we don't have to do the workaround, so ff-calls are  
cheaper.