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    SubjectRe: [RFC,PATCH] cfq-iosched: improve async queue ramp up formula
    On Thu, Nov 26 2009, Corrado Zoccolo wrote:
    > The introduction of ramp-up formula for async queue depths has
    > slowed down dirty page reclaim, by reducing async write performance.
    > This patch improves the formula by considering the remaining slice.
    >
    > The new formula will allow more dispatches at the beginning of the
    > slice, reducing them at the end.
    > This will ensure that we achieve good throughput, without the risk of
    > overrunning the allotted timeslice.
    >
    > The threshold is automatically increased when sync I/O is not
    > intermingled with async, in accordance with the previous incarnation of
    > the formula.

    The slow ramp up is pretty much essential to being able to have low
    latency for the sync reads, so I'm afraid this will break that. I would
    prefer doing it through memory reclaim detection, like the other patch
    you and Motohiro suggested.

    --
    Jens Axboe



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