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    SubjectRe: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3
    On Sat, Jul 24, 2010 at 11:07:07AM +0200, Corrado Zoccolo wrote:
    > On Sat, Jul 24, 2010 at 10:51 AM, Christoph Hellwig <hch@infradead.org> wrote:
    > > To me this sounds like slice_idle=0 is the right default then, as it
    > > gives useful behaviour for all systems linux runs on.
    > No, it will give bad performance on single disks, possibly worse than
    > deadline (deadline at least sorts the requests between different
    > queues, while CFQ with slice_idle=0 doesn't even do this for readers).

    > Setting slice_idle to 0 should be considered only when a single
    > sequential reader cannot saturate the disk bandwidth, and this happens
    > only on smart enough hardware with large number of spindles.

    I was thinking of writting a user space utility which can launch
    increasing number of parallel direct/buffered reads from device and if
    device can sustain more than 1 parallel reads with increasing throughput,
    then it probably is good indicator that one might be better off with
    slice_idle=0.

    Will try that today...

    Vivek


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