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    SubjectRe: [PATCH V2 1/2] block: Make cfq_target_latency tunable through sysfs.
    On 2012-03-31 08:31, Tao Ma wrote:
    > From: Tao Ma <boyu.mt@taobao.com>
    >
    > In cfq, when we calculate a time slice for a process(or a cfqq to
    > be precise), we have to consider the cfq_target_latency so that all the
    > sync request have an estimated latency(300ms) and it is controlled by
    > cfq_target_latency. But in some hadoop test, we have found that if
    > there are many processes doing sequential read(24 for example), the
    > throughput is bad because every process can only work for about 25ms
    > and the cfqq is switched. That leads to a higher disk seek. We can
    > achive the good throughput by setting low_latency=0, but then some
    > read's latency is too much for the application.
    >
    > So this patch makes cfq_target_latency tunable through sysfs so that
    > we can tune it and find some magic number which is not bad for both
    > the throughput and the read latency.

    Thanks, applied both.

    --
    Jens Axboe



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