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    SubjectRe: deadline unfairness
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    Hello Aron,

    On Saturday 22 March 2008, Aaron Carroll wrote:
    > Bernd Schubert wrote:
    > > Hello,
    > >
    > > some it seems the deadline scheduler is rather unfair. Below is an
    > > example of md-raid6 initialization of md3, md4 and md5. All three
    > > md-devices do share the same blockdevices (we have patched md to allow
    > > parallel rebuild of shared block devices, since for us the cpu is the
    > > bottleneck and not the block device).
    > >
    > > All rebuilds started basically at the same time, as you can see, md3 is
    > > already done and now md4 rebuilds substantially faster than md5.
    > > [..]
    > > This is basically with a 2.6.22 kernel + lustre + md-backports, but
    > > nothing done to the scheduler.
    >
    > Hi Bernd,
    >
    > There is a deadline bug in pre-2.6.24 kernels where lower-sector requests
    > can starve higher-sector requests; you might be hitting this bug. It was
    > fixed by commit: 6f5d8aa6382eef2b26032c88656270bdae7f0c42

    thanks a lot for your help! I will build a new kernel later on today and then
    report back if it helps. Commit dfb3d72a9aa519672c9ae06f0d2f93eccb35482f also
    looks useful...

    Thanks again,
    Bernd


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