Mac OS X versus Linux

Lmbench 2.04 provides a suite of micro benchmarks that measure the bottlenecks at the Unix operating system and CPU level. This makes it very suitable for testing the theory that Mac OS X might be the culprit for the terrible server performance of the Apple platform.

Signals allow processes (and thus threads) to interrupt other processes. In a database system such as MySQL 4.x where so many processes/threads (60 in our MySQL screenshot) and many accesses to the kernel must be managed, signal handling is a critical performance factor.

Larry McVoy (SGI) and Carl Staelin (HP):
" Lmbench measure both signal installation and signal dispatching in two separate loops, within the context of one process. It measures signal handling by installing a signal handler and then repeatedly sending itself the signal."
Host OS Mhz null null
call
open
I/O
stat slct
clos
sig
TCP
sig
inst
Xeon 3.06 GHz Linux 2.4 3056 0.42 0.63 4.47 5.58 18.2 0.68 2.33
G5 2.7 GHz Darwin 8.1 2700 1.13 1.91 4.64 8.60 21.9 1.67 6.20
Xeon 3.6 GHz Linux 2.6 3585 0.19 0.25 2.30 2.88 9.00 0.28 2.70
Opteron 850 Linux 2.6 2404 0.08 0.17 2.11 2.69 12.4 0.17 1.14

All numbers are expressed in microseconds, lower is thus better. First of all, you can see that kernel 2.6 is in most cases a lot more efficient. Secondly, although this is not the most accurate benchmark, the message is clear: the foundation of Mac OS X server, Darwin handles the signals the slowest. In some cases, Darwin is even several times slower.

As we increase the level of concurrency in our database test, many threads must be created. The Unix process/thread creation is called "forking" as a copy of the calling process is made.

lmbench "fork" measures simple process creation by creating a process and immediately exiting the child process. The parent process waits for the child process to exit. The benchmark is intended to measure the overhead for creating a new thread of control, so it includes the fork and the exit time.

lmbench "exec" measures the time to create a completely new process, while " sh" measures to start a new process and run a little program via /bin/ sh (complicated new process creation).

Host OS Mhz fork
hndl
exec
proc
Sh
proc
Xeon 3.06 GHz Linux 3056 163 544 3021
G5 2.7 GHz Darwin 2700 659 2308 4960
Xeon 3.6 GHz Linux 3585 158 467 2688
Opteron 850 Linux 2404 125 471 2393

Mac OS X is incredibly slow, between 2 and 5(!) times slower, in creating new threads, as it doesn't use kernel threads, and has to go through extra layers (wrappers). No need to continue our search: the G5 might not be the fastest integer CPU on earth - its database performance is completely crippled by an asthmatic operating system that needs up to 5 times more time to handle and create threads.

Mac OS X: beautiful but… Workstation, yes; Server, no.
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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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