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.

IBM PowerPC 970FX: Superscalar monster Benchmark configuration
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  • edchi - Tuesday, June 26, 2007 - link


    I haven't tried this yet, but will do tomorrow. Here is what Apple suggests to create a better MySQL installation:

    http://docs.info.apple.com/article.html?artnum=303...">http://docs.info.apple.com/article.html?artnum=303...
    Reply
  • grantma - Tuesday, April 18, 2006 - link

    I found Gnome was a lot more snappy than OS X desktop under Debian PowerPC. You could tell the kernel was far faster using Linux 2.6 - programs would just start immediately. Reply
  • pecosbill - Wednesday, June 15, 2005 - link

    I'm not going to waste my time searching to see if these same comments below were made already, but the summary of them is those who are performance oriented tune their code for a CPU. You can do the same for an OS. Also, the "Big Mac" cluster in VA tech speaks otherwise to raw performance as OS X was the OS of choice. From macintouch.com:

    Okay, stop, I have to make an argument about why this article fails, before I explode. MySQL has a disgusting tendency to fork() at random moments, which is bad for performance essentially everywhere but Linux. OS X server includes a version of MySQL that doesn't have this issue.
    No real arguments that Power Macs are somewhat behind the times on memory latency, but that's because they're still using PC3200 DDR1 memory from 2003. AMD/Intel chips use DDR2 or Rambus now ... this could be solved without switching CPUs.
    The article also goes out of its way to get bad results for PPC. Why are they using an old version of GCC (3.3.x has no autovectorization, much worse performance on non-x86 platforms), then a brand spanking new version of mySQL (see above)? The floating point benchmark was particularly absurd:

    "The results are quite interesting. First of all, the gcc compiler isn't very good in vectorizing. With vectorizing, we mean generating SIMD (SSE, Altivec) code. From the numbers, it seems like gcc was only capable of using Altivec in one test, the third one. In this test, the G5 really shows superiority compared to the Opteron and especially the Xeons"

    In fact, gcc 3.3 is unable to generate AltiVec code ANYWHERE, except on x86 where they added a special SSE mode because x87 floating point is so miserable. This could have been discovered with about 5 minutes of Google research. It wouldn't had to have been discovered at all if they hadn't gone out of their way to use a compiler which is the non-default on OS X 10.4. Alarm bells should have been going off in the benchmarkers head when an AMD chips outperforms an Intel one by 3x, but, anyway ...
    I hate to seem like I'm just blindly defending Apple here, but this article seems to have been written with an agenda. There's no way one guy could stuff this much stuff up. To claim there's something inherently wrong with OS X's ability to be a server is going against so much publicly available information it's not even funny. Notice Apple seems to have no trouble getting Apache to run with Linux-like performance: [Xserve G5 Performance].
    Anyway ... on a more serious note, a switch of sorts to x86 may not be a hugely insane idea. IBM's ability to produce a low power G5 part seems to be seriously in question, so for PowerBooks Apple is pretty much running out of options. Worse comes to worst - if they started selling x86-powered portables, that might get IBM to work a bit harder to get them faster desktop chips.
    -- "A Macintosh MPEG software developer"
    Reply
  • aladdin0tw - Tuesday, June 14, 2005 - link

    This is my first time to see someone use 'ab' command to conduct a test, and trying to tell us something from the test.

    In my opinion, ab is never a 'stress test' tool for any reason, especially when you want to conclude some creditable benchmark from this test. If we can accept 'ab', why I have to code so much for a stress test?

    The 'localhost' is another problematic area, DNS. Why not using a fixed ip as an address? The first rule of benchmaking is isolated the domain in question, but I can not see you obey these rule. So how can you interpret your result as a performance faulty, not a dns related problem?

    I think you should benchmark again, and try some good practices used in software industry.

    Aladdin from Taiwan
    Reply
  • demuynckr - Sunday, June 12, 2005 - link

    jhagman, the number in the apache test table means the request per second that the server handles. Reply
  • jhagman - Wednesday, June 08, 2005 - link

    Hi again, demuynckr.

    Could you please answer to me, or preferably add the information to the article. What the does the number in the apache test table mean and what kind of a page was loaded?

    I assumed that the numbers given were hits per second or transfer rate. I've been testing a bit on my powerbook (although with a lower n) and I can very easily beat the numbers you have. So it is apparent that my assumption was wrong.

    BTW, gcc-3.3 on Tiger knows the switch -mcpu=G5
    Reply
  • rubikcube - Wednesday, June 08, 2005 - link

    I thought I would post this set of benchmarks for os x on x86 vs. PPC. Even though XBench is a questionable benchmark, it still is capable of vindicating these questions about linux-ppc.

    http://www.macrumors.com/pages/2005/06/20050608063...
    Reply
  • webflits - Wednesday, June 08, 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 :)."

    I believe you :)

    But why my are results I get way higher than the numbers listed in the article?
    Reply
  • mongo lloyd - Tuesday, June 07, 2005 - link

    At least the non-ECC RAM, that is. Reply
  • mongo lloyd - Tuesday, June 07, 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? Reply

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