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    SubjectRe: [PATCH] [RFC] Add support for uevents on block device idle changes
    On Thu, Nov 19, 2009 at 02:29:29PM +0100, Kay Sievers wrote:
    > On Thu, Nov 19, 2009 at 14:01, Matthew Garrett <mjg@redhat.com> wrote:
    > > On Thu, Nov 19, 2009 at 12:09:30PM +0100, Kay Sievers wrote:
    > >> On Wed, Nov 18, 2009 at 22:33, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
    > >> > My use cases are on the order of a second.
    > >>
    > >> Ok, what's the specific use case, which should be triggered after a
    > >> second? I thought you were thinking about disk spindown or similar.
    > >
    > > The first is altering ALPM policy. ALPM will be initiated by the host if
    > > the number of queued requests hits zero - if there's no hysteresis
    > > implemented, then that can result in a significant performance hit. We
    > > don't need /much/ hysteresis, but it's the difference between a 50%
    > > performance hit and not having that.
    >
    > Can't that logic live entirely in the kernel, instead of being a
    > rather generic userspace event interface (with the current limitation
    > to a single user)?

    It could, but it seems a bit of a hack. It'd still also require the
    timer to be in the kernel, so we might as well expose that to userspace.

    --
    Matthew Garrett | mjg59@srcf.ucam.org


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