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    SubjectRe: CFQ will be the new default IO scheduler - why?
    Al Boldi wrote:
    > Arjan van de Ven wrote:
    >>>> 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.
    >> Hi,
    >
    > Hi!
    >
    >> 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.
    >
    > IC. That probably explains why concurrent io-procs have such a hard time
    > getting through to the disk. They probably just hang in the flatting phase,
    > waiting for something to take care of their requests.
    >
    flattening is just an addition in the cpu, that's just really boring and shouldn't be visible anywhere
    performance wise
    -
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