[TriLUG] Re: Fedora Core 2 Test 1 (FC2t1) initial impressions

Jeremy Portzer jeremyp at pobox.com
Fri Feb 13 10:00:03 EST 2004


On Fri, 2004-02-13 at 09:32, Nathan Conrad wrote:
> Theer are two major things that the 2.6 kernel does very closely with
> glibc: threading and syscalls.
> 
> On newer x86 CPUs, and maybe some other architectures the method that
> userspaces uses to make syscalls has changed a lot. It should be much
> faster now.
> 
> The method of creating threads is different too. I'm pretty sure that
> with 2.4, threads we just sub-processes and the kernel didn't know
> that they were actually threads. With 2.6, the kernel knows that a
> thread is a thread and is able to schedule time for threads more
> appropriately and efficiently (fewer context changes, I think).  This
> new technology is called NPTL, Natix Posix Thread Library.

This is actually the Native Posix Thread Library, and it has been
available in Red Hat Linux since version 8.0, and therefore also Fedora
Core 1.  These distributions used 2.4 kernels but the 2.6 code for NPTL
was "back-ported" to the heavily-patched 2.4 kernels in Red Hat.  I
believe at least one other distribution has done this too.  So any
performance gains from FC1 to FC2t1 can't be attributed solely to NPTL.

Another back-ported feature from 2.6 that's been available in Red Hat
kernels for several versions is the "O(1) scheduler" .  This vastly
improves the efficiency for scheduling, which is the important procedure
that determines which processes/threads get processor time.  Because a
multitasking kernel switches processes very often, the scheduler gets
run extremely frequently.  Ingo Molnar -- one of the more accomplished
kernel developers -- came up with the O(1) scheduler which means that
the scheduler takes just about the same amount of time regardless of the
number of processes being juggled.

--Jeremy

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