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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.

    One seek is still 10msec on modern drive, right? So 4k seeks =
    40seconds, no? 4seconds would correspond to 1msec per seek, which
    seems low.

    writes with O_SYNC could force full seek on each request, right?
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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