[CentOS] ppc questions
Bryan J. Smith
b.j.smith at ieee.org
Thu Sep 15 14:25:56 UTC 2005
Karanbir Singh <mail-lists at karan.org> wrote:
> Linux wins hands down.
There are two major contributors to this:
1. Until just recently (GCC 4.x), the PPC64 GCC target was
very poor. Apple leverages GCC 3.x in current MacOS
2. The pre-emptive Mach microkernel adds overhead and
context switching, although it has helped maintain
portability (including to x86).
[ NOTE: Despite the insistance of Microsoft marketeers, the
NT Hardware Abstraction Layer (HAL) is _not_ a microkernel,
and it does _not_ pre-empt the NT kernel. If it did, NT
would be much slower. ]
> I am sitting typing this out on a Dual G5 2ghz, and I
> find Linux to be much more responsive than OSX.
Hmmm, "responsiveness" is not a complete test of performance.
In fact, prior to the pre-empt patch, based on just
"responsiveness," a single CPU Linux system would be near the
bottom of the barrel.
Responsiveness v. throughput is always a game played --
typically between microkernels and monolithic kernels.
Microkernels typically have better response time, monolithic
kernels typically have better throughput. Microkernels make
re-entry (kernel threading) easier, monolithic kernels make
it more difficult. These are oversimplifications, but you
get the jist.
Ironically enough, although the Mach component of MacOS X is
a microkernel, you're running on the Darwin platform which is
monolithic. Linux is a monolithic kernel with a couple of
approaches to re-entry. I don't like the pre-empt patch,
because it is a hack to take adavantage of Linus' ingenious
ideal to allow 1 kernel entry per CPU to keep context
switching down. That design is specific to the number of
physical cores, and overall performance is hurt by the
In the near-future of dual-core designs, I hope the kernel
goes back to 1 entry per CPU. It gives you adequate response
time without hurting throughput because there is no
additional context switching overhead -- each CPU has a
single thread. Linus was a genious in coming up with that.
> anandtech had a write-up recently where they compared OSX
> Server to Linux on the server side of things, iirc
> correctly - Linux came out on top. A bit of googling
> should dig up the exact article.
It dependend on the application. AnandTech actually made it
a 2-parter, investigating more after the first run.
One also needs to remember that Darwin/Cocoa is not a true,
"clean" 64-bit platform.
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