The G5 a.k.a. Power 970FX

You might not have noticed it, but there is in fact a lot of good news in this article for owners of current Apple systems. Gcc 4.0 promises a lot better (FP) performance in open source software. The improvement from gcc 4.0 over gcc 3.3.3 and 3.3 is amazing on the PowerFX family: almost a 70% improved FP performance!

Now that the open source community finally has a decent compiler for the Apple platform, Apple management decides to step over to another architecture. Ironically, right now, the Intel architecture needs a super-optimized compiler (Intel's own) to reach the FP performance that the G5 now reaches with a very popular but far less aggressive compiler (gcc).

Combined with the data from our first article, we can safely say that the G5 2.7 GHz FP performance is at least as good as the best x86 CPUs. Integer performance seems to be between 70% and 80% of the fastest x86 CPUs, while FP/SIMD performance can actually surpass x86 in certain situations.

With the dual-core Power 970MP available and IBM's current outstanding track record when it comes to multi-core CPUs, big question marks can be placed on whether or not the switch to Intel CPUs will - from a technical point of view - be such a big step forward as Steve Jobs claims. There is more: each core has 1 MB cache instead of the current 512 KB, which will improve integer performance quite a bit as it lessens the impact of the biggest problem of the G5 - the high latency access to the memory system.

Xserve, silently cooled. Below the G5 with the cover, you can see the heatsink.

It is again ironic that the Power 970MP is far more advanced than the current Intel Dual-cores when it comes to power management. Each core can be placed independently in a power-saving state called doze, while the other core continues operation.

A low power Power 970FX is also available and consumes about 16 Watts at 1.6 GHz; so it seems that IBM, although slightly late, could have provided everything that Apple needs. The G5 with its 58 million transistors and 66 mm² die size is not really a hot CPU. The Xserve (2 x 2.3 GHz G5) was by far the quietest 1U air-cooled server that ever entered our lab in Kortrijk.

The Usual Suspects

The Mac OS X kernel environment includes the Mach kernel, BSD, the I/O Kit, file systems, and networking components. Some of these components slow down MySQL significantly. While our rough profiling has not identified the true culprits, we think that we can narrow the possible suspects to:
  1. Relatively high TCP Latency that we measured
  2. The implementation of the threading system. Does the pthread to Mach threads mapping involve some overhead, or is this the result of the traditional performance problem of the micro kernel, namely the high latency of such a kernel on system calls? While Mac Os X is not a micro-kernel, the problem might still exist as the Mach core is deep inside that kernel. Is there IPC overhead? Lmbench signaling benchmarks seem to suggest that there is.
  3. The finer grained locking in the current version of Tiger does not appear to be working for some reason and we still have the "two lock" system of Panther.
Will this performance problem only be visible in MySQL? At this point, we can only speculate, but we have a strong suspicion that this is not the case. Server workloads spend, contrary to other workloads such as workstation apps, a substantial portion of their execution in the kernel and TCP stack. Porting such applications to Mac OS X is more complicated than just recompiling code. We didn't have to search long before we found examples of companies that increased their number of servers or upgraded in order to run MySQL faster.

We look forward to testing other database and server apps on the Mac OS X platform. Critical reports that point out weaknesses can only help the Apple community move forward and keep the Apple people on their toes.


[1] Threading on OS X

[2] Lmbench: Portable Tools for Performance Analysis
Larry McVoy, Silicon Graphics
Carl Staelin, Hewlett-Packard Laboratories

[3] Performance Characterization of a Quad Pentium Pro SMP Using OLTP
Kimberly Keeton*, David A. Patterson*, Yong Qiang He+, Roger C. Raphael+, and Walter E. Baker
Computer Science Division
University of California at Berkeley

Mac OS X Achilles Heel
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  • tthiel - Wednesday, May 24, 2006 - link

    You need to redo this entire test. So much has come out about how poorly this was done its hard to believe it came from Anandtech.
  • iggie - Friday, January 13, 2006 - link

    I'm surprised you didn't post the raw VM latency results from lmbench. I found">another article that did a similar performance comparison (Darwin vs. Linux on G5).
    mmap latency is 3x greater, but most tellingly, page fault latency is > 900 x greater!

    Did you observe similar results in your tests?

    I would imagine that page faults would play a greater and greater role as more and more independent clients connect to a server. I have experienced a huge disparity in">our own server software implementation for scientific imaging. In our case, all disk access is done via mmap and page faults (its a shared-VM-based image server system meant to serve many terabytes of image data)
  • asifyoucare - Sunday, September 4, 2005 - link

    Interesting article.

    If you suspect that thread performance is the bottleneck, why not write a short program to measure how many threads can be created and destroyed per second?

  • DoctorBooze - Saturday, September 3, 2005 - link


    In the case of Linux, creating a thread is very similar to creating a process. [...] So, if you test fork() on Linux, you also get a rough idea of how fast threads are created

    I'm no guru but I don't think that's true now with Native Posix Threads, which you get in 2.6 kernels with a suitable libc (and some distros with 2.4 kernels). Check what your program's linked with: on my Fedora Core 3 system `ldd /usr/libexec/mysqld` shows me MySQL is linked with /lib/tls/ and running that shows it has NPTL. The API may be similar but what happens in the kernel isn't and it makes a big, big difference to MySQL. Still, Linux now has fast native POSIX threads and it looks like OS X doesn't.
  • ikruusa - Saturday, September 3, 2005 - link

    Indeed, as mentioned previously there was some mistakes in gcc options. And SIMD optimization is really basic in 4.0.x - only certain loops can be vectorized automatically. But loops around arrays are most significant part in signal processing and that is where SIMD really matters :)
    As we know for NetBurst arch it is recommended to use XMM registers (that is registers for SSE/SSE2) for FP calculations. And that is what gcc 3.x does (4.x too): -mfpmath=sse triggers all x87 stuff to run as scalar math using SSE command-set. As I know AltiVec is SIMD unit which is smoothly added to PowerPC pipeline. How useful there is scalar math instead of usual FP - I have no idea.
    What I want to say - my opinion is that if MySQL team has something to say about compiler options then they have documents about it. Using SIMD style processing in DB engine is very challenging exercise for coders. Dont expect magic from compiler here. Hint: maybe Intel's own icc compiler provide some magic but you have to prove it ;) I still believe that the most useful options can be -O[2,3] -funroll-loops and -ffast-math (as you mentioned) with -arch=[processor]. The last one should provide basic branching elimination (e.g. using cmov for x86) and correct instr. ordering.
    About testing Linux. I have some skills in Apache testing with JMeter. I have been quite stuck but kernel developers were kind enough to help:">
    Then I discovered all OS tuning possibilities in /proc Well, most are still unknown for me but I just want to get your attention here. Oracle talks about shared memory and number of semaphores and some particular Linux /proc parameters. Of course there should be all written in MySQL manual too if any parameter needs tuning. But is it enough to read MySQL manual and create profile for OS'es IPC and process management if we need to stress test MySQL on e.g 8-way SMP?
    But still - good start of interesting investigation,!! Thank you and keep going!
  • kvs - Saturday, September 3, 2005 - link

    If thread-creation is extremely slow in Darwin, maybe MySQL-performance could be helped by enabled the thread cache? A look at 'mysqladmin extended-status' would show how many threads had been created and cached, and should reveal if thread_cache would be needed.
  • tester2 - Friday, September 2, 2005 - link

    Well if ab on Mac OS X was the problem you could have easily tested this from a Linux box over the network.

    Because you probably did this as well, and found out that performance tuning done by Apple outperformed the Linux/PPC and Linux/Opteron system by a substantial amount you keept this out of the story ...

    So I did some testing, and yes when using ab from a Mac OS X I find the exact figures you report. Using a Linux Pentium 4 based system over Gb network gave me 6150 req/sec substantially faster then anything out there.
    Look here for numbers from another source;,1895,1637655,">,1895,1637655,

    The webserver runs around 60 threads ... go figure.

    Yes there is a problem with the Mac OS X - Mysql combo if you are looking for performance, but jugging this as Mac OS X for server applications is a nono is drawing the wrong conclusion. I hope someone with good development skills will look at the mysql code and tune it to work well with Mac OS X.

  • benh - Friday, September 2, 2005 - link

    Interesting article ! One thing that is worth looking into however is wether the YDL kernel is actually a 32 or a 64 bits kernel. This would probably have an impact on some of the numbers. I would expect the ppc64 kernel to perform faster overall on a 64 bits CPU with a small overhead on syscalls from 32 bits applications due to the argument size translation.

    Also, the problem with the 2.7Ghz on linux is indeed a slight change in the firmware. It in fact looks like a bug in Apple Open Firmware device tree on those machine where they left out the properties providing the interrupt routing of the i2c controller in the north bridge used to drive the fan controller among others. The OS X driver silently falls back to a polled mecanism, while the linux driver doesn't and (shame on me!) used to have a small bug that would cause it crash when unable to locate those properties.

    I posted a patch a while ago fixing that up, I would expect YDL to have an updated kernel/installer available by now.

    Finally, you are right about the U3 northbridge having a quite high memory latency, that is definitely not helping the G5. There have been rumours floating around that Apple now has a new bridge that improves that significantly, though it's pretty much impossible to tell if/when they will release a machine using it. IBM also had multicore G5s available for some time now, though Apple is still not releasing any machine using them.

  • JohanAnandtech - Friday, September 2, 2005 - link

    Thanks for the very helpful feedback.

    Do you have any idea why the U3 came with such high latency. Lack of development time? Lack of expertise? A inherent problem with the FSB of the G5? Rather old technology? You see I am very curious, and couldn't find much info on it.

  • benh - Friday, September 2, 2005 - link

    I don't know for sure. I wouldn't blame the FSB though. I remember reading somewhere that the memory controller in U3 was similar if not identical to the old one they used in U2 on G4 machines and was to blame but I can't guarantee the reliability of that information.

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