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    SubjectRe: The well-factored 386
    On Tue, Jul 29, 2003 at 01:59:41PM +0100, you [John Bradford] wrote:
    > > > I didn't realise he was talking about an x86 emulator. I thought he
    > > > was analyzing real hardware.
    > > >
    > > > The one thing that made it on-topic for me was his quiet suggestion
    > > > that "forreal" mode interrupts are faster, and that it might, perhaps,
    > > > be possible to modify a Linux kernel to run in that mode - to take
    > > > advantage of the faster interrupts.
    > >
    > > That would have to be a kernel for very special use. The "forreal"
    > > mode has protection turned off. As far as I know, that
    > > means any user process can take over the cpu as if
    > > it was running in kernel mode.
    > >
    > > Perhaps useful for some embedded use with only a couple well-tested
    > > processes running. Still, a programming error could overwrite
    > > kernel memory instead of segfaulting.
    >
    > Anything that's single user and non-networked isn't beyond the realms
    > of feasability - it would be useful for a games console, or high
    > performance graphics work.
    >
    > It would be an interesting project, but what concerns me is how well
    > implemented these non-standard modes actually are. It's possible that
    > there are processors out there that don't work reliably with them, or
    > don't implement them at all.

    Have you looked at Kernel Mode Linux?

    http://web.yl.is.s.u-tokyo.ac.jp/~tosh/kml/

    I don't think it uses "forreal" mode, but it allows running selected user
    processes in kernel mode thus getting rid of system call overhead.

    [Note to Toshiyuki Maeda: the complete thread is at
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=utf-8&threadm=expl.8vH.27%40gated-at.bofh.it&rnum=1&prev=/groups%3Fq%3DThe%2Bwell-factored%2B386%26num%3D50%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3Dutf-8%26sa%3DN%26tab%3Dwg
    in case you want to catch some context. The "forreal" idea is mentioned in
    the first mail of the thread.]


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