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    SubjectRe: An elevator algorithm (patch)
    On 18 Sep 2000, Peter Osterlund wrote:
    > Andrea Arcangeli <andrea@suse.de> writes:
    >
    > > > The only disadvantage I can see is that the new patch doesn't handle
    > > > consecutive insertions in O(1) time, but then again, the pre-latency
    > >
    > > We can still do that by trivially fixing a bit your code. You should first
    > > check if the new inserted request is over the last in the current queue before
    > > entering the tmp1/tmp2 logic.
    >
    > Yes this can be done, but it will affect where requests are inserted.
    > Suppose the queue currently contains:
    >
    > 100 200 300 400 10 20 30
    >
    > If request 150 is to be inserted, then with my previous patch it
    > will be inserted between 100 and 200, but with the proposed
    > change it will instead be inserted at the end.

    This is a bug in Andrea's idea. The request should only
    be inserted at the end of the list if:

    1) the block numbre is bigger than head->prev (which you
    already have)

    AND

    2) the block number is smaller than head (or head->next
    if the current request is unplugged)

    regards,

    Rik
    --
    "What you're running that piece of shit Gnome?!?!"
    -- Miguel de Icaza, UKUUG 2000

    http://www.conectiva.com/ http://www.surriel.com/

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