No more mysteries: Apple's G5 versus x86, Mac OS X versus Linux
by Johan De Gelas on June 3, 2005 7:48 AM EST- Posted in
- Mac
Workstation, yes; Server, no.
The G5 is a gigantic improvement over the previous CPU in the PowerMac, the G4e. The G5 is one of the most superscalar CPUs ever, and has all the characteristics that could give Apple the edge, especially now that the clock speed race between AMD and Intel is over. However, there is still a lot of work to be done.First of all, the G5 needs a lower latency access to the memory because right now, the integer performance of the G5 leaves a lot to be desired. The Opteron and Xeon have a better integer engine, and especially the Pentium 4/Xeon has a better Branch predictor too. The Opteron's memory subsystem runs circles around the G5's.
Secondly, it is clear that the G5 FP performance, despite its access to 32 architectural registers, needs good optimisation. Only one of our flops tests was " Altivectorized", which means that the GCC compiler needs to improve quite a bit before it can turn those many open source programs into super fast applications on the Mac. In contrast, the Intel compiler can vectorize all 8 tests.
Altivec or the velocity engine can make the G5 shine in workstation applications. A good example is Lightwave where the G5 takes on the best x86 competition in some situations, and remains behind in others.
The future looks promising in the workstation market for Apple, as the G5 has a lot of unused potential and the increasing market share of the Power Mac should tempt developers to put a little more effort in Mac optimisation.
The server performance of the Apple platform is, however, catastrophic. When we asked Apple for a reaction, they told us that some database vendors, Sybase and Oracle, have found a way around the threading problems. We'll try Sybase later, but frankly, we are very sceptical. The whole "multi-threaded Mach microkernel trapped inside a monolithic FreeBSD cocoon with several threading wrappers and coarse-grained threading access to the kernel", with a "backwards compatibility" millstone around its neck sounds like a bad fusion recipe for performance.
Workstation apps will hardly mind, but the performance of server applications depends greatly on the threading, signalling and locking engine. I am no operating system expert, but with the data that we have today, I think that a PowerPC optimised Linux such as Yellow Dog is a better idea for the Xserve than Mac OS X server.
References
Threading on OS Xhttp://developer.apple.com/technotes/tn/tn2028.html
Basics OS X
http://developer.apple.com/documentation/macosx/index.html
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michaelok - Saturday, June 4, 2005 - link
"with one benchmark showing that the PowerMac is just a mediocre PC while another shows it off as a supercomputer, the unchallenged king of the personal computer world."Well, things are a little different when you connect, say, 32768 processors together, i.e. you go from running MySQL to Teradata, so yes, the Power architecture seems to dominate, and the Virginia Tech supercomputer is still up there, at 7th.
http://www.top500.org/lists/plists.php?Y=2004&...
" The RISC ISA, which is quite complex and can hardly be called "Reduced" (The R of RISC), provides 32 architectural registers"
'Reduced Instruction Set' is misleading, it actually refers to a design philosophy of using *smaller, simpler* instructions, instead of a single complex instruction. This is to be compared with the Itanium for example, which Intel calls 'EPIC' (Explicit Parallel Instruction Computing), but it is essentially derived from VLIW (Very Long Instruction Word).
Anyway, nice article, certainly much more to discuss here, such as SMT (Simultaneous Multithreading), (when that is available for the Apple :), vs. Intel's Hyperthreading. We'll still be comparing Apples to Oranges but isn't that why everybody buys the Motor Trend articles, i.e. '68 Mustang vs. '68 GT?
psychodad - Saturday, June 4, 2005 - link
I agree. Recently I read a review which pitted macs against pcs using software blatantly optimized for macs. If you have ever used unoptimized software, you will know it. It is slow, often unstable and not at all usable, especially if you're after productivity.Viditor - Friday, June 3, 2005 - link
IntelUser2000 - "about the AMD TDP number, they never state that its max power, they say its maximum power achievable under most circumstances, its not absolute max power"Not true at all...AMD's datasheet clearly states that it's not only max power, but max theoretical power.
http://www.amd.com/us-en/assets/content_type/Downl...
trooper11 - Friday, June 3, 2005 - link
I think its hard enough comparing a G5 to PC systems. I dont belive there will ever be a 'fair' comparison that satisfies everyone on both sides. There are too few general programs to compare and people will always complain about using or not using optimized apps for either platform. many of the varibles are subjective and the benchmarks to be compared are so heavily debated without a clear answer.I think this was a good attempt, but I gave up trying to 'fairly' compare the two a long time ago. Anyhting that sheds a bit of light is a good thing, but i never expect an end to the contreversy, too many questions that cant be answered.
I would though love to see the addition of dual core amd chips since they are out there and would be serious competition, of course it would fly in server applications. hopefully the numbers for that could be added in a later article.
psychodad - Friday, June 3, 2005 - link
Fascinating. You run these tests using a compiler that Apple does not use (unless it is Yellow Dog) against software generally optimized for x86 architectures and you make conclusions. This makes your data tainted (actually biased) and your conclusions faulty. I would suggest that in fairness you make your tests more "real world" by using the software compiled by compilers that the rest of us nontechnical people use on a daily basis.smitty3268 - Friday, June 3, 2005 - link
Rosyna:Oh, I assumed he was using the Apple version of gcc. If not, then I see what you mean.
crimsonson - Friday, June 3, 2005 - link
This article may be moot by Mondayhttp://tinyurl.com/7ex4v
Garyclaus16 - Friday, June 3, 2005 - link
" Oh and the graph on page 5 doesnt display correctly in firefox. "AND you are using firefox for what reason?...you deserve to view pages incorrectly
Rosyna - Friday, June 3, 2005 - link
smitty3268, that's part of the problem. Almost no one uses GCC 3.3.3 (stock, from the main gcc branch) for Mac OS X development because it really sucks at optimizing for the PPC. On the other hand, OS X was compiled with the Apple shipped GCC 3.3/GCC 4.0.smitty3268 - Friday, June 3, 2005 - link
I think its fair to use the compilers most people are going to be using. That would be gcc on both platforms. As far as autovectorization in 4.0, don't expect very much from it. Obviously it will be better than 3.3, but the real work is being added now in 4.1.I'll join the other 50 posters who would have liked to see at least 1 page showing the G5's performance under linux compared to OSX. That and maybe a few more real world benchmarks. But your article was very informative and answered a lot of questions. It was frustrating that there really wasn't anything done like this before.