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    SubjectRe: Compatible with i386/UP but optimised for i686/SMP [was Re: test_and_set_bit() not atomic forever?]
    Hi,

    > > >The point was that lots of people are running SMP kernels on UP machines,
    > > >where it's gratuitous overhead.
    > >
    > > Then they shouldn't do that.
    >
    > Unless they're a distributor who wants to run one kernel per
    > architecture, + modules.

    You cannot avoid significant slowdown with SMP kernel on UP machines
    due to extra locking needed.

    > Or a sysadmin, in a situation where managing different kernels for that
    > extra bit of efficiency isn't worth the administrative overhead.

    When you need to have a single kernel for lots of similar machines,
    they are usually UP, so compiling a SMP kernel doesn't make sense.

    > These points apply also to the i386/i486/i586/i686 optimisation issue.
    > Is it worth making a kernel nearly optimised for i686 but compatible
    > with i386? (Perhaps using fixups in the same way to blank out calls to
    > do the "verify put_user" type stuff, vs. blanking out flush_tlb and so
    > forth?)

    It would make sense to distribute three kernels:

    - i386

    - i586

    - i586 SMP

    Have a nice fortnight
    --
    Martin `MJ' Mares <mj@ucw.cz> http://atrey.karlin.mff.cuni.cz/~mj/
    Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
    "The computer is mightier than the pen, the sword, and usually, the programmer."

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