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
Summary: the cores compared
Below, you find a comparison of the Intel Xeon/Pentium 4, the Opteron/Athlon 4, the G5 and the previous CPU in the Apple Power: the G4 of Motorola.CPU feature |
Motorola G4+ |
G5 (IBM PowerPC 970) |
Intel Xeon P4 Irwindale |
AMD Opteron Troy |
Process technology |
0.18 µ CU SOI |
0.09 µ CU SOI |
0.09 µ CU |
0.09 µ CU SOI |
GP Register Width (bit) |
32 |
64 |
64 |
64 |
Number of transistors (Million) |
33 |
58 |
169 |
106 |
Die Size (mm²) |
106 |
66 |
+/-130 (112 for 1 MB L2) |
115 |
Maximum Clockspeed (MHz) |
1400 |
2700 (liquid cooled) |
3800 |
2600 |
Pipeline Stages ( fp) |
7 |
16 (21) |
31 - 39* |
12 (17) |
issue rate (Instruction per clockcycle) |
3 + 1 Branch |
4 + 1 branch |
4 ports, max. 6 (3 sustained) |
6 (3 sustained) |
Integer issue rate (IPC) |
3 + 1 Branch |
2 |
4 (3 sustained) |
3 |
Floating point issue rate (IPC) |
1 |
2 |
1 |
3 |
Vector issue rate (IPC) |
2-4 ( Altivec) |
2-4 ( Altivec, velocity) |
4 Single(SSE-2/3) |
4 Single(SSE-2/3) |
2 Double (SSE-2/3) |
2 Double (SSE-2/3) |
|||
Load & Store units |
1 |
2 |
2 |
2 |
"instructions in flight" (OOO Window) |
16 |
215 (100) |
126 |
72 |
Branch History Table size (entries) |
2048 |
16384 |
4096 |
16384 |
L1-cache (Instruction/Data) |
32 KB/32 KB |
64 KB/32 KB |
12k µops (+/- 8-16 KB)/16 KB |
64 KB/64KB |
L2-cache |
256 KB |
512 KB |
2048 KB |
1024 KB |
L3-cache |
2 MB DDR SRAM 64 bit at 1/4 th of core clock |
none |
None |
none |
Front Side Bus (MHz) |
166 |
1350 (675 DDR) |
800 (200 Quad) |
N/A |
Front Side Bus (GB/s) |
1.3 Half Duplex |
10,8 Full Duplex |
6.4 Half Duplex |
N/A |
Memory Bandwidth (GB/s) |
2.7 |
6.4 |
6.4 |
6.4 |
Core Voltage |
1.6V |
1,1V ? |
1.38V |
1.4V |
Power Dissipation |
30W at 1 GHz |
+/- 59 (Typical) -80 Watt (max) |
110 W (Typical) |
92,6W (Max) |
*31 is branch misprediction pipeline length, 39 is the length of the total pipeline including decoding stages before the trace cache.
Let us summarize: in theory, the PowerPc 970FX is a very wide, deeply pipelined superscalar monster chip, with excellent Branch prediction and fantastic features for streaming applications. And let us not forget the two parallel FPUs and the SIMD Altivec unit, which can process up to 4 calculations per clock cycle.
The disadvantages are the rather coarse way that the 970FX handles the instruction flow and the high latency to the RAM.
Enough theory. Let us see how the G5 2.5 GHz and 2.7 GHz compares to the 3.6 GHz Xeon Irwindale and Opteron 250 (2.4 GHz). The Opteron 852 arrived just a day before my deadline, but I think that you will know how the 252 performs compared to the 250. Before we tackle performance, here are a few quick notes about power dissipation.
Power to the PowerPC
How power thirsty is this PowerPC 970FX? His predecessor, the 0.13µ SOI PowerPC 970 was a pretty cool chip. It consumed about 42W at 1.8 GHz (1.3v). The newer 0.09µ SOI PowerPC 970FX CPU is reported to dissipate about 55-59W at 2.5 GHz. However, a few annotations must be made.First of all, IBM and Apple tend to increase the core voltage when running at higher clock speed. This makes the needed power increase more than linearly. For example, the 1.8 GHz PowerPC 970 consumed 42 Watt, but the 2 GHz version (both 0.13µ CPUs) needed 66 Watt.
Secondly, the TDP IBM talks about is typical , not maximum like AMD's.
Let us clarify this by checking IBM's and Apple's numbers. For the 90 nm, IBM's own documents tell us that the PowerPC 970FX only consumes 24.5 Watt at 2 GHz (1V). However, the same 0.09µ SOI PowerPC970FX is reported to consume about 55W at 2.3 GHz (1.1V?) in the Xserve, according to Apple's own website. Typically, you would expect the G5 to consume about 28 Watt (24.5 * 2.3 / 2) at 2.3 GHz, when using the 24.5 Watt at 2 GHz as a reference. Apple talks about "at most" (maximum), and IBM about "typical".
Still, that is a huge gap between "typical" and "maximum" power dissipation. The 55 Watt number seems to indicate that the core voltage must have been increased significantly at 2.3 GHz. The maximum power dissipation of the 2.5/2.7 GHz G5 inside the liquid-cooled PowerMacs might thus be quite a bit higher than in the 1U Xserve, probably around 80 Watt for the 2.7 GHz. That is a lot of power for a 66 mm² CPU, and it probably explains why Apple introduced liquid cooling. The liquid cooling system inside our PowerMac wouldn't get warm and wouldn't be necessary at all if the two 2.5 GHz CPUs were only dissipating a 59 Watt maximum.
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mongo lloyd - Tuesday, June 7, 2005 - link
At least the non-ECC RAM, that is.mongo lloyd - Tuesday, June 7, 2005 - link
Any reason for why you weren't using RAM with lower timings on the x86 processors? Shouldn't there at least have been a disclaimer?jhagman - Tuesday, June 7, 2005 - link
OK, this clears it up, thanks.One little thing still, what is the number you are giving in the ab results table? Is it requests per second or perhaps the transfer rate?
demuynckr - Tuesday, June 7, 2005 - link
jhagman:As i mentioned before, we used gcc 3.3.3 for all linux, and gcc 3.3 mac compiler on apple, because that was the standard one.
I did a second flops test with the gcc 4.0 compiler included on the Tiger cd, and the flops are much better when compiled with the -mcpu=g5 option which did not seem available when using the gcc 3.3 Apple compiler.
As for ab i used these settings,
ab -n 100000 -n x http://localhost/
x for the various concurrencies: 5,20,50,100,150.
spinportal - Monday, June 6, 2005 - link
Guess there's no one arguing that the PPC is not keeping its paces with the current market, but rather OS/X able to do Big Iron computing. And if rumors be true, where will you be able to get a PPC built once Apple drops IBM for Intel?In a Usenet debate in 93, Torvalds and Tannenbaum go roasting Mach microkernel vs. the death of Linux. Seems Linus' work will be seeing more light of day, and Mach go the way of the dodo. Will Apple rewrite OS/X for Intel x86/64? As far as practical business sense, that's like shooting off one's leg foot.
spinportal - Monday, June 6, 2005 - link
jhagman - Monday, June 6, 2005 - link
Could you please give the exact method of testing apache with ab? It is really hard to try to redo the tests when one does not know which methodology was used. The amount of clients and switches of ab would be appreciated.Also an answer to why Apple's newest gcc (4.0) was not used would be an interesting one and did you _really_ use gcc 3.3.3 and not Apple's gcc?
Other than these omissions I found the article very interesting, thanks.
demuynckr - Monday, June 6, 2005 - link
Yes I have read the article, I also personally compiled the microbenchmarks on linux as well as on the PPC, and I can tell you I used gcc 3.3 on Mac for all compilation needs :).webflits - Monday, June 6, 2005 - link
demuynckr, did your read the article?"So, before we start with application benchmarks, we performed a few micro benchmarks compiled on all platforms with the SAME gcc 3.3.3 compiler. "
BTW I ran the same tests using Apple's version of gcc 3.3
As you can see my 2.0Ghz now beats the 2.5Ghz on 5 of the 8 tests, and a 2.7Ghz G5 would be on par with the Opteron 250 when you extrapolate the results.
Lets face it, Anandtech screwed up by using a crippled compiler for the G5 tests
----------------------------
GCC 3.3/OSX 10.4.1/2.0GHz G5
FLOPS C Program (Double Precision), V2.0 18 Dec 1992
Module Error RunTime MFLOPS
(usec)
1 4.0146e-13 0.0140 997.2971
2 -1.4166e-13 0.0108 648.4622
3 4.7184e-14 0.0089 1918.5122
4 -1.2546e-13 0.0139 1076.8597
5 -1.3800e-13 0.0312 928.9079
6 3.2374e-13 0.0182 1596.1407
7 -8.4583e-11 0.0348 344.3954
8 3.4855e-13 0.0196 1527.6638
Iterations = 512000000
NullTime (usec) = 0.0004
MFLOPS(1) = 827.5658
MFLOPS(2) = 673.7847
MFLOPS(3) = 1037.6825
MFLOPS(4) = 1501.7226
demuynckr - Monday, June 6, 2005 - link
Just to clear things up: on linux the gcc 3.3.3 was used, on macintosh gcc 3.3 was used (the one that was included with the OS).