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    SubjectRe: [Lse-tech] Re: 10.31 second kernel compile
    In article <>,
    Momchil Velikov <> wrote:
    >Out of curiousity, why there's a need to update the linux page tables ?
    >Doesn't pte/pmd/pgd family functions provide enough abstraction in
    >order to maintain _only_ the hashed page table ?

    No. The IBM hashed page tables are not page tables at all, they are
    really just a bigger 16-way set-associative in-memory TLB.

    You can't actually sanely keep track of VM layout in them.

    Those POWER4 machines are wonderful things, but they have a few quirks:

    - it's so expensive that anybody who is slightly price-conscious gets a
    farm of PC's instead. Oh, well.

    - the CPU module alone is something like .5 kilowatts (translation:
    don't expect it in a nice desktop factor, even if you could afford

    - IBM nomenclature really is broken. They call disks DASD devices, and
    they call their hash table a page table, and they just confuse
    themselves and everybody else for no good reason. They number bits
    the wrong way around, for example (and big-endian bitordering really
    _is_ clearly inferior to little-endian, unlike byte-ordering. Watch
    the _same_ bits in the _same_ register change name in the 32 vs
    64-bit architecture manuals, and puke)

    But with all their faults, they do have this really studly setup with 8
    big, fast CPU's on a single module. A few of those modules and you get
    some ass-kick performance numbers. As you can see.

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