 | | | Slow Path Bugs in OpenGL on Intel and Rosetta | Slow Path Bugs in OpenGL on Intel and Rosetta 2007-05-07 - By zmorris@(protected)
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Hi All, I decided to take a couple of days and write a test app to
show the speed of various paths for uploading an image from a GWorld
to OpenGL. It's loosely based on concepts from Apple's OpenGL Image
example. You can download the app here:
http://homepage.mac.com/zmorris/.Public/opengltexture.zip
I decided to write it because a lot of games run slowly under Rosetta
(like 12 fps!), and I think it is mainly caused by bottlenecks
uploading a 16 bit texture in a 32 bit context. This is bad because
people inadvertently run older copies of PowerPC games under Rosetta
and can get a bad impression of the games. There are also some
really bad bottlenecks running as native Intel.
The following functions have serious bugs:
glTexImage2D() <- slow emulation in Rosetta, slow path in Intel
glDrawPixels() <- slow emulation in Rosetta
These need to be fixed immediately for Mac OS 10.4 and up on Intel.
Known Macs that are affected: Mac Mini, MacBook...
Slow path means that something went catastrophically wrong and it is
running on the order of 10 fps.
This probably means that Apple hasn't optimized the path at all yet,
meaning it uses something like a for-loop to blit pixels.
Slow emulation means that something is running slower than 30 fps in
Rosetta.
This probably means that the path is still calling powerpc code
instead of native intel opengl code.
Please read README.txt in the download for the full explanation.
It would really help a lot if some of you could download the test app
and run both the PPC and Intel versions, and then email result
(intel).txt, result(ppc).txt, and/or result(rosetta).txt to this
group so we can get some confirmation.
Here are the results for our dual core Mac Mini, running first the
powerpc code and then intel code:
######### result(rosetta).txt #########
ProductName: Mac OS X
ProductVersion: 10.4.9
BuildVersion: 8P2137
readable-model: not found
hw.model: PowerMac
hw.machine: Power Macintosh
hw.ncpu: 2
hw.byteorder: 4321
hw.cpufrequency: 1830000000
hw.busfrequency: 664000000
kern.version: Darwin Kernel Version 8.9.1: Thu Feb 22 20:55:00 PST
2007; root:xnu-792 (See http://xnu-792.ora-code.com).18.15~1/RELEASE_I386
kern.osrelease: 8.9.1
kern.osrevision: 199506
sysctl.proc_native: 0
opengl-vendor: Intel Inc.
opengl-renderer: Intel GMA 950 OpenGL Engine
opengl-version: 1.2 APPLE-1 (See http://PLE-1.ora-code.com).4.52
width: 640
height: 480
1 flush-window........ 13.4881 ms 74.1394 fps
2 CopyBits-window..... 4.60818 ms 217.005 fps
3 16-video-window..... 40.7782 ms 24.5229 fps (slow-emulation!)
4 32-video-window..... 3.95584 ms 252.791 fps
5 16-system-window.... 134.188 ms 7.45221 fps (slow-path!)
6 32-system-window.... 12.288 ms 81.3804 fps
7 16-video-fullscreen. 40.8088 ms 24.5045 fps (slow-emulation!)
8 32-video-fullscreen. 7.15986 ms 139.667 fps
9 16-system-fullscreen 133.847 ms 7.47123 fps (slow-path!)
0 32-system-fullscreen 12.5991 ms 79.371 fps
######### result(intel).txt #########
ProductName: Mac OS X
ProductVersion: 10.4.9
BuildVersion: 8P2137
readable-model: Mac mini (Core Duo/Solo)
hw.model: Macmini1,1
hw.machine: i386
hw.ncpu: 2
hw.byteorder: 1234
hw.cpufrequency: 1830000000
hw.busfrequency: 664000000
kern.version: Darwin Kernel Version 8.9.1: Thu Feb 22 20:55:00 PST
2007; root:xnu-792 (See http://xnu-792.ora-code.com).18.15~1/RELEASE_I386
kern.osrelease: 8.9.1
kern.osrevision: 199506
sysctl.proc_native: 1
opengl-vendor: Intel Inc.
opengl-renderer: Intel GMA 950 OpenGL Engine
opengl-version: 1.2 APPLE-1 (See http://PLE-1.ora-code.com).4.52
width: 640
height: 480
1 flush-window........ 13.4305 ms 74.4575 fps
2 CopyBits-window..... 5.99009 ms 166.942 fps
3 16-video-window..... 2.49084 ms 401.471 fps
4 32-video-window..... 3.51515 ms 284.483 fps
5 16-system-window.... 72.747 ms 13.7463 fps (slow-path!)
6 32-system-window.... 10.2054 ms 97.987 fps
7 16-video-fullscreen. 6.13679 ms 162.952 fps
8 32-video-fullscreen. 6.97913 ms 143.284 fps
9 16-system-fullscreen 72.8877 ms 13.7197 fps (slow-path!)
0 32-system-fullscreen 10.5174 ms 95.0804 fps
####################################
Notice the slow path cases even on native intel that are only getting
13 fps, while right next to them are nearly identical cases that are
getting FOUR HUNDRED fps. Keep in mind that all of these are moving
pixels from system memory to video memory. At worst, there should be
a factor of 2-4 difference but no more. This is why I had to post
the code. It seems unbelievable, but the bugs really are this bad.
I am tired of people not believing me. For people googling this, I
first posted about it here:
http://lists.apple.com/archives/Mac-games-dev/2006/Jan/msg00031.html
There was a lot of code to sift through, but we knew the bottleneck
would be in a handful of functions. We thought they were event
related but it turns out they were mostly in OpenGL, which shouldn't
really be emulated at all in the first place, when you think about it.
For everyone wondering why we chose this particular method to draw
our games, it's all explained in the README, so please read that
first. We have tried every possible way we could think of, and we
believe that this is the best method for retro style games that do
their drawing in system memory.
For anyone still in doubt, does it seem a bit disconcerting that
these bottlenecks exist? How many more could there be? And does
this help to explain why Mac versions of games often get half the
frame rate of their PC equivalents?
If worse comes to worse, at least you get some handy opengl texturing
examples and system profiling code :)
Thank you all for your help,
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
Zack Morris Z Sculpt Entertainment This Space
zmorris@(protected) http://www.zsculpt.com For Rent
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
If the doors of perception were cleansed, everything would appear to man
as it is, infinite. -William Blake, The Marriage of Heaven and Hell
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