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    SubjectRe: IO scheduler based IO controller V10

    * Jens Axboe <> wrote:

    > It's not _that_ easy, it depends a lot on the access patterns. A good
    > example of that is actually the idling that we already do. Say you
    > have two applications, each starting up. If you start them both at the
    > same time and just care for the dumb low latency, then you'll do one
    > IO from each of them in turn. Latency will be good, but throughput
    > will be aweful. And this means that in 20s they are both started,
    > while with the slice idling and priority disk access that CFQ does,
    > you'd hopefully have both up and running in 2s.
    > So latency is good, definitely, but sometimes you have to worry about
    > the bigger picture too. Latency is more than single IOs, it's often
    > for complete operation which may involve lots of IOs. Single IO
    > latency is a benchmark thing, it's not a real life issue. And that's
    > where it becomes complex and not so black and white. Mike's test is a
    > really good example of that.

    To the extent of you arguing that Mike's test is artificial (i'm not
    sure you are arguing that) - Mike certainly did not do an artificial
    test - he tested 'konsole' cache-cold startup latency, such as:

    sh -c "perf stat -- konsole -e exit" 2>&1|tee -a $LOGFILE

    against a streaming dd.

    That is a _very_ relevant benchmark IMHO and konsole's cache footprint
    is far from trivial. (In fact i'd argue it's one of the most important
    IO benchmarks on a desktop system - how does your desktop hold up to
    something doing streaming IO.)


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      Last update: 2009-10-02 19:23    [W:0.022 / U:6.108 seconds]
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