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

Gary Byers gb at clozure.com
Wed Mar 18 10:09:47 UTC 2009


<http://clozure.com/pipermail/openmcl-devel/2009-January/008832.html>
tried to answer the same question when it was asked a few weeks later.

On Wed, 18 Mar 2009, R. Matthew Emerson wrote:

>
> 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.
>
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>



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