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    SubjectRe: CFQ will be the new default IO scheduler - why?

    > > Should there be a default scheduler per filesystem? As some filesystems
    > > may perform better/worse with one over another?
    > It's currently perDevice, and should probably be extended to perMount.


    per mount is going to be "not funny". I assume the situation you are
    aiming for is the "3 partitions on a disk, each wants its own elevator".
    The way the kernel currently works is that IO requests the filesystem
    does are first flattened into an IO for the entire device (eg the
    partition mapping is done) and THEN the IO scheduler gets involved to
    schedule the IO on a per disk basis.
    The 2.4 kernel did this the other way around, and it was really a bad
    idea (no fairness, less optimal scheduling all around due to less
    visibility into what the disk is really doing, several hardware
    properties such as TCQ depth that affect scheduling IOs are truely per
    disk not per partition etc etc)

    So I don't think it's likely that per mount is really an option right

    Arjan van de Ven

    if you want to mail me at work, send mail to arjan (at)

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      Last update: 2006-07-24 18:35    [W:0.019 / U:4.872 seconds]
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