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    SubjectRe: cfq-iosched: tiobench regression
    On Fri, Dec 25, 2009 at 06:16:27PM +0800, Corrado Zoccolo wrote:
    > Hi Shaohua,
    > On Thu, Dec 24, 2009 at 1:55 AM, Shaohua Li <shaohua.li@intel.com> wrote:
    > > df5fe3e8e13883f58dc97489076bbcc150789a21
    > > b3b6d0408c953524f979468562e7e210d8634150
    > > The coop merge is too aggressive. For example, if two tasks are reading two
    > > files where the two files have some adjecent blocks, cfq will immediately
    > > merge them. cfq_rq_close() also has trouble, sometimes the seek_mean is very
    > > big. I did a test to make cfq_rq_close() always checks the distence according
    > > to CIC_SEEK_THR, but still saw a lot of wrong merge. (BTW, why we take a long
    > > distence far away request as close. Taking them close doesn't improve any thoughtput
    > > to me. Maybe we should always use CIC_SEEK_THR as close criteria).
    > Yes, when deciding if two queues are going to be merged, we should use
    > the constant CIC_SEEK_THR.
    Ok, will prepare a seperate patch for this.

    > > So sounds we need make split more aggressive. But the split is too lazay,
    > > which requires to wait 1s. Time based check isn't reliable as queue might not
    > > run at given time, so uses a small time isn't ok.
    > 1s is too much, but I wouldn't abandon a time based approach. To fix
    > the problem of queue not being run, you can consider a slice. If at
    > the end of the slice, the queue is seeky, you split it.
    Sounds good, will take this way.

    Thanks,
    Shaohua


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