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
The G5 as Server CPU
While it is the Xserve and not the PowerMac that is Apple's server platform, we could not resist the temptation to test the G5 based machine as a server too. Installed on the machine was the server version of Mac OS X Tiger. So in fact, we are giving the Apple platform a small advantage: the 2.5 GHz CPUs are a bit faster than the 2.3 GHz of the Xserve, and the RAM doesn't use ECC as in the Xserve.
| Dual G5 2,5 GHz PowerMac | Dual Xeon DP 3,6 GHz (HT on) | Dual Xeon DP 3,6 GHz (HT out) | Dual Opteron 2.4Ghz | |
| 1 | 192 | 286 | 287 | 290 |
| 2 | 274 | 450 | 457 | 438 |
| 5 | 113 | 497 | 559 | 543 |
| 10 | 62 | 517 | 583 | 629 |
| 20 | 50 | 545 | 561 | 670 |
| 35 | 50 | 486 | 573 | 650 |
| 50 | 47 | 495 | 570 | 669 |
Performance is at that point only 1/10th of the Opteron and Xeon. We have tested this on Panther (10.3) and on Tiger (10.4.1), triple-checked every possible error and the result remains the same: something is terribly wrong with the MySQL server performance.
SPEC CPU 2000 Int numbers compiled with GCC show that the G5 reaches about 75% of the integer performance of an equally clocked Opteron. So, the purely integer performance is not the issue. The Opteron should be quite faster, but not 10 times faster.
We checked with the activity monitor, and the CPUs were indeed working hard: up to 185% CPU load on the MySQL process. Notice that the MySQL process consists of no less than 60 threads.
| Concurrency | Dual Powermac G5 2.5 GHz (Panther) | Dual Powermac G5 2.7 GHz (Tiger) | Dual Xeon 3.6 GHz |
| 5 | 216.34 | 217.6 | 3776.44 |
| 20 | 216.24 | 217.68 | 3711.4 |
| 50 | 269.38 | 218.32 | 3624.63 |
| 100 | 249.51 | 217.69 | 3768.89 |
| 150 | 268.59 | 256.89 | 3600.1 |
The new OS, Tiger doesn't help: the 2.7 GHz (10.4.1) is as fast as the 2.5 GHz on Panther (10.3). More importantly, Apache shows exactly the same picture as MySQL: performance is 10 times more worse than on the Xeon (and Opteron) on Linux. Apple is very proud about the Mac OS X Unix roots, but it seems that the typical Unix/Linux software isn't too fond of Apple. Let us find out what happened!
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exdeath - Friday, June 3, 2005 - link
Wow look at a 2.4 GHz Opteron clean house.I'd like to see what a 2.6 GHz FX-55 with unregistered memory would do ;) I'll be fair and say keep it at 2.6 GHz stock ;)
bersl2 - Friday, June 3, 2005 - link
Right. GCC 4.0 has an all new optimization framework, including autovectorization:http://gcc.gnu.org/projects/tree-ssa/vectorization...
Pannenkoek - Friday, June 3, 2005 - link
It is well known that GCC 3.3 can't vectorize code. However, GCC 4 should be able to, eventually if not already.The small cache of the G5 would hamper its server performance I'd reckon, regardless of other factors.
jimbailey - Friday, June 3, 2005 - link
I'm curious if you rebuilt Apache and MySQL from source. Apple has added significant amount of optimization to gcc and I would love to know if it has been included in this test. I don't doubt the results though. The trade off for using the Mach micro-kernel is well known.rubikcube - Friday, June 3, 2005 - link
Johan, I agree that all the facts point to your conclusions being accurate. I would bet all the money in the world that you are correct. However, this hypothesis is easily confirmed by running mysql on a G5 running linux.Olaf van der Spek - Friday, June 3, 2005 - link
> In Unix, this is done with a Syscall, and it results in two context switches (the CPU has to swap out one process for another)Does it?
As far as I know it doesn't. The page tables don't need to be swapped and neither does the CPU state. The CPU gets access to the kernel-data because it goes to kernel-mode, but that doesn't require a full context switch I think.
WileCoyote - Friday, June 3, 2005 - link
Tough crowd...Eug - Friday, June 3, 2005 - link
Of the stuff I understand, I agree with your conclusions, but I think it's reasonable to state that running Linux on the G5 yourself would have been the most definitive test.Anyways, I like fusion food. :)
cHodAXUK - Friday, June 3, 2005 - link
Great article, very educational read and it was very interesting to see what is holding the G5 back. IBM/Apple really need to address these issues, people are paying alot of money for G5's that are dilvering nowhere near the level of performance that they *theoretically* should be.Netopia - Friday, June 3, 2005 - link
WOW... great article.I too would like to see Yellow Dog (Or FC4) loaded on the G5 for a true head-to-head. I hope you have the time with the box to get 'er done!
Joe