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    SubjectRe: Linux disk performance.
    On Mon, Dec 18, 2006 at 06:24:39PM +0545, Manish Regmi wrote:
    > On 12/18/06, Arjan van de Ven <> wrote:
    > >if you want truely really smooth writes you'll have to work for it,
    > >since "bumpy" writes tend to be better for performance so naturally the
    > >kernel will favor those.
    > >
    > >to get smooth writes you'll need to do a threaded setup where you do an
    > >msync/fdatasync/sync_file_range on a frequent-but-regular interval from
    > >a thread. Be aware that this is quite likely to give you lower maximum
    > >performance than the batching behavior though.
    > >
    > Thanks...
    > But isn't O_DIRECT supposed to bypass buffering in Kernel?

    It is.

    > Doesn't it directly write to disk?

    Yes, but it still uses an IO scheduler.

    > I tried to put fdatasync() at regular intervals but there was no
    > visible effect.

    In your first message you mentioned you were using an ancient 2.6.10
    kernel. That kernel uses the anticipatory IO scheduler. Update to the
    latest stable kernel ( at time of writing) and it will default
    to the CFQ scheduler which has a smoother writeout, plus you can give
    your process a different IO scheduling class and level (see

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      Last update: 2006-12-18 14:21    [W:0.021 / U:65.864 seconds]
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