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    SubjectRe: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
    Andrew Morton wrote:

    >Nick Piggin <piggin@cyberone.com.au> wrote:
    >
    >>That is what I can't understand. Movement of the disk head should
    >>be exactly the same in either situation and 128K is not exactly
    >>a pitiful request size - so it suggests a quirk somewhere. It
    >>is not as if the disk has to be particularly smart or know a
    >>lot about the data in order to optimise the head movement for
    >>a load like this.
    >>
    >
    >Yes, that's a bit odd. Some reduction in CPU cost and bus
    >traffic, etc would be expected. Could be that sending out a
    >request which is larger than a track is saving a rev of the disk
    >for some reason.
    >
    Shouldn't be. Even at 128KB readahead we should always have
    outstanding requests against the disk in a streaming read
    scenario, right? Maybe if the track buffers are bigger than
    128K?

    Is there a magic number above which you see the improvement,
    Andrea? Or does it steadily climb?

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