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SubjectRe: what's next for the linux kernel?
On Sun, Oct 02, 2005 at 05:05:42PM -0400, Rik van Riel wrote:
> On Sun, 2 Oct 2005, Luke Kenneth Casson Leighton wrote:
>
> > and, what is the linux kernel?
> >
> > it's a daft, monolithic design that is suitable and faster on
> > single-processor systems, and that design is going to look _really_
> > outdated, really soon.
>
> Linux already has a number of scalable SMP synchronisation
> mechanisms.

... and you are tied in to the decisions made by the linux kernel
developers.

whereas, if you allow something like a message-passing design (such as
in the port of the linux kernel to l4), you have the option to try out
different underlying structures - _without_ having to totally redesign
the infrastructure.

several people involved with the l4linux project have already done
that: as i mentioned in the original post, there are about three or
four different and separate l4 microkernels available for download
(GPL) and one of them is ported to stacks of different architectures,
and one of them is SMP capable and even includes a virtual machine
environment.

and they're only approx 30-40,000 lines each, btw.


also, what about architectures that have features over-and-above SMP?

in the original design of SMP it was assumed that if you have
N processors that you have N-way access to memory.

what if, therefore, someone comes up with an architecture that is
better than or improves greatly upon SMP?

they will need to make _significant_ inroads into the linux kernel
code, whereas if, say, you oh i dunno provide hardware-accelerated
parallel support for a nanokernel (such as l4) which just _happens_
to be better than SMP then running anything which is l4 compliant gets
the benefit.


the reason i mention this is because arguments about saying "SMP is it,
SMP is great, SMP is everything, we're improving our SMP design" don't
entirely cut it, because SMP has limitations that don't scale properly
to say 64 or 128 processors: sooner or later someone's going to come up
with something better than SMP and all the efforts focussed on making
SMP better in the linux kernel are going to look lame.

l.

p.s. yes i do know of a company that has improved on SMP.

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