Re: 2.2.18Pre Lan Performance Rocks!

Jeff V. Merkey
2000-10-31T23:01:32Z

David Lang wrote:
>
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> Jeff, one other thing. Linux is not x86 hand-crafted assembler, it's
> capable of running on many platforms. are you planning on giving up this
> capability or hand crafting the kernel for each chip?
>
> Linux on x86 is nice (and I do use it a lot) but one of the things that
> makes it so useful is that when you do outgrow what youcan do on a x86
> platform you cna move to a more powerful platform without having to change
> to a different OS.

How about a NetWare like NOS with all the application support of Linux?
I think a lot of people will love it. Novell's largest customers have
told me they want to see it, and would deploy it. I do believe there's
a market for such a beast. A very lucrative one...

Jeff

>
> David Lang
>
> On Tue, 31 Oct 2000,
> Jeff V. Merkey wrote:
>
> > Date: Tue, 31 Oct 2000 15:45:45 -0700
> > From: Jeff V. Merkey <jmerkey@timpanogas.org>
> > To: Andi Kleen <ak@suse.de>, mingo@elte.hu, Pavel Machek <pavel@suse.cz>,
> > linux-kernel@vger.kernel.org
> > Subject: Re: 2.2.18Pre Lan Performance Rocks!
> >
> >
> >
> > One more optimization it has. NetWare never "calls" functions in the
> > kernel. There's a template of register assignments in between kernel
> > modules that's very strict (esi contains a WTD head, edi has the target
> > thread, etc.) and all function calls are jumps in a linear space.
> > layout of all functions are 16 bytes aligned for speed, and all
> > arguments in kernel are passed via registers. It's a level of
> > optimization no C compiler does -- all of it was done by hand, and most
> > function s in fast paths are layed out in 512 byte chunks to increases
> > speed. Stack memory activity in the NetWare kernel is almost
> > non-existent in almost all of the "fast paths"
> >
> > Jeff
> >
> > "Jeff V. Merkey" wrote:
> > >
> > > A "context" is usually assued to be a "stack". The simplest of all
> > > context switches
> > > is:
> > >
> > > mov x, esp
> > > mov esp, y
> > >
> > > A context switch can be as short as two instructions, or as big as a TSS
> > > with CR3 hardware switching,
> > >
> > > i.e.
> > >
> > > ltr ax
> > > jmp task_gate
> > >
> > > (500 clocks later)
> > >
> > > ts->eip gets exec'd
> > >
> > > you can also have a context switch that does an int X where X is a gate
> > > or TSS.
> > >
> > > you can also have a context switch (like linux) that does
> > >
> > > mov x, esp
> > > mov esp, y
> > > mov z, CR3
> > > mov CR3, w
> > >
> > > etc.
> > >
> > > In NetWare, a context switch is an in-line assembly language macro that
> > > is 2 instructions long for a stack switch and 4 instructions for a CR3
> > > reload -- this is a lot shorter than Linux.
> > > Only EBX, EBP, ESI, and EDI are saved and this is never done in the
> > > kernel, but is a natural
> > > affect of the Watcom C compiler. There's also strict rules about
> > > register assignments that re enforced between assembler modules in
> > > NetWare to reduce the overhead of a context switch. The code path is
> > > very complex in NetWare, and priorities and all this stuff exists, but
> > > these code paths are segragated so these types of checks only happen
> > > once in a while and check a pre-calc'd "scoreboard" that is read only
> > > across processors and updated and recal'd by a timer every 18 ticks.
> > >
> > > Jeff
> > >
> > >
> > >
> > > Andi Kleen wrote:
> > > >
> > > > On Tue, Oct 31, 2000 at 02:52:11PM -0700, Jeff V. Merkey wrote:
> > > > > The numbers don't lie. You know where the code is. You notice that
> > > > > there is a version of
> > > > > the kernel hand coded in assembly language. You'l also noticed that
> > > > > it's SMP and takes ZERO LOCKS during context switching, in fact, most of
> > > > > the design is completely lockless.
> > > >
> > > > I suspect most of the confusion in this thread comes because you seem to
> > > > use a different definition of context switch than Ingo and others. Could
> > > > you explain what you exactly mean with a context switch ?
> > > >
> > > > -Andi
> > -
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> >
>
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