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    SubjectRe: [PATCH linux-2.6-block:master 02/05] blk: update ioscheds to use generic dispatch queue
    On Fri, Oct 21 2005, Tejun Heo wrote:
    > I think we're currently talking about two issues.

    I think so too :)

    > 1. Is @sort=0 case useful?
    >
    > Currently all ioscheds dispatch requests in sorted order. I was
    > afraid that sorting again might result in less efficient seek pattern
    > although I'm not quite sure whether or how that will happen. That's why
    > I added the @sort argument to elv_dispatch_insert(). If sorting cannot
    > hurt in any case, we might sort unconditionally and remove @sort
    > argument from elv_dispatch_insert().

    That's what I ended up merging, elv_dispatch_sort() and it only takes q
    and rq as parameters.

    > 2. Why @force is used to turn on @sort?

    Yes, that was my question :-)

    > The reasoning was that, when a iosched is forced dispatched, it
    > doesn't have control over many aspects of IO scheduling, so it cannot
    > produce good ordering of dumped requests, which actually is true for
    > cfq. That's why @sort is turned on while force-dispatching requests.

    Well that's not quite my question, it is the opposite - why would you
    not want to sort?

    > Maybe just removing @sort argument from elv_dispatch_insert() and
    > sorting always is the way to go?

    See the merged stuff, I think so. I just don't see any reason at all to
    tie 'force' and 'sort' together.

    --
    Jens Axboe

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