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    SubjectRe: [RESEND][RFC] BFQ I/O Scheduler
    On Thu, Apr 17 2008, Paolo Valente wrote:
    > Pavel Machek ha scritto:
    > >
    > >>In the first type of tests, to achieve a higher throughput than CFQ
    > >>(with the default 100 ms time slice), the maximum budget for BFQ
    > >>had to be set to at least 4k sectors. Using the same value for the
    > >>
    > >
    > >Hmm, 4k sectors is ~40 seconds worst case, no? That's quite long...
    > >
    > Actually, in the worst case among our tests, the aggregate throughput
    > with 4k sectors was ~ 20 MB/s, hence the time for 4k sectors ~ 4k * 512
    > / 20M = 100 ms.

    That's not worse case, it is pretty close to BEST case. Worst case is 4k
    of sectors, with each being a 512b IO and causing a full stroke seek.
    For that type of workload, even a modern sata hard drive will be doing
    500kb/sec or less. That's rougly a thousand sectors per seconds, so ~4
    seconds worst case for 4k sectors.

    Jens Axboe

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