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    SubjectRe: [RFC PATCH] block: Change default IO scheduler to deadline except SATA
    On 2012-04-10 15:37, Vivek Goyal wrote:
    > Hi,
    > I am wondering if CFQ as default scheduler is still the right choice. CFQ
    > generally works well on slow rotational media (SATA?). But often
    > underperforms on faster storage (storage arrays, PCIE SSDs, virtualized
    > disk in linux guests etc). People often put logic in user space to tune their
    > systems and change IO scheduler to deadline to get better performance on
    > faster storage.
    > Though there is not one good answer for all kind of storage and for all
    > kind of workloads, I am wondering if we can provide a better default and
    > that is change default IO scheduler to "deadline" except SATA.
    > One can argue that some SAS disks can be slow too and benefit from CFQ. Yes,
    > but default IO scheduler choice is not perfect anyway. It just tries to
    > cater to a wide variety of use cases out of the box.
    > So I am throwing this patch out see if it flies. Personally, I think it
    > might turn out to be a more reasonable default.

    I think it'd be a lot more sane to just use CFQ on rotational single
    devices, and default to deadline on raid or non-rotational devices. This
    still isn't perfect, since less worthy SSDs still benefit from the
    read/write separation, and some multi device configs will be faster as
    well. But it's better.

    The below patch is not a good idea. There's no clear distinction between
    on what CFQ is now the default.

    Jens Axboe

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