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    SubjectRe: IO scheduler based IO controller V10
    On Fri, Oct 02 2009, Ingo Molnar wrote:
    >
    > * Jens Axboe <jens.axboe@oracle.com> wrote:
    >
    > > It's not hard to make the latency good, the hard bit is making sure we
    > > also perform well for all other scenarios.
    >
    > Looking at the numbers from Mike:
    >
    > | dd competing against perf stat -- konsole -e exec timings, 5 back to
    > | back runs
    > | Avg
    > | before 9.15 14.51 9.39 15.06 9.90 11.6
    > | after [+patch] 1.76 1.54 1.93 1.88 1.56 1.7
    >
    > _PLEASE_ make read latencies this good - the numbers are _vastly_
    > better. We'll worry about the 'other' things _after_ we've reached good
    > latencies.
    >
    > I thought this principle was a well established basic rule of Linux IO
    > scheduling. Why do we have to have a 'latency vs. bandwidth' discussion
    > again and again? I thought latency won hands down.

    It's really not that simple, if we go and do easy latency bits, then
    throughput drops 30% or more. You can't say it's black and white latency
    vs throughput issue, that's just not how the real world works. The
    server folks would be most unpleased.

    --
    Jens Axboe



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