[Openmcl-devel] OpenGL Performance PPC vs Intel-Mac 32/64
R. Matthew Emerson
rme at clozure.com
Wed Mar 18 07:04:10 UTC 2009
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.
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
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